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Linux/fs/namei.c

  1 /*
  2  *  linux/fs/namei.c
  3  *
  4  *  Copyright (C) 1991, 1992  Linus Torvalds
  5  */
  6 
  7 /*
  8  * Some corrections by tytso.
  9  */
 10 
 11 /* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
 12  * lookup logic.
 13  */
 14 /* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture.
 15  */
 16 
 17 #include <linux/init.h>
 18 #include <linux/export.h>
 19 #include <linux/kernel.h>
 20 #include <linux/slab.h>
 21 #include <linux/fs.h>
 22 #include <linux/namei.h>
 23 #include <linux/pagemap.h>
 24 #include <linux/fsnotify.h>
 25 #include <linux/personality.h>
 26 #include <linux/security.h>
 27 #include <linux/ima.h>
 28 #include <linux/syscalls.h>
 29 #include <linux/mount.h>
 30 #include <linux/audit.h>
 31 #include <linux/capability.h>
 32 #include <linux/file.h>
 33 #include <linux/fcntl.h>
 34 #include <linux/device_cgroup.h>
 35 #include <linux/fs_struct.h>
 36 #include <linux/posix_acl.h>
 37 #include <linux/hash.h>
 38 #include <asm/uaccess.h>
 39 
 40 #include "internal.h"
 41 #include "mount.h"
 42 
 43 /* [Feb-1997 T. Schoebel-Theuer]
 44  * Fundamental changes in the pathname lookup mechanisms (namei)
 45  * were necessary because of omirr.  The reason is that omirr needs
 46  * to know the _real_ pathname, not the user-supplied one, in case
 47  * of symlinks (and also when transname replacements occur).
 48  *
 49  * The new code replaces the old recursive symlink resolution with
 50  * an iterative one (in case of non-nested symlink chains).  It does
 51  * this with calls to <fs>_follow_link().
 52  * As a side effect, dir_namei(), _namei() and follow_link() are now 
 53  * replaced with a single function lookup_dentry() that can handle all 
 54  * the special cases of the former code.
 55  *
 56  * With the new dcache, the pathname is stored at each inode, at least as
 57  * long as the refcount of the inode is positive.  As a side effect, the
 58  * size of the dcache depends on the inode cache and thus is dynamic.
 59  *
 60  * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
 61  * resolution to correspond with current state of the code.
 62  *
 63  * Note that the symlink resolution is not *completely* iterative.
 64  * There is still a significant amount of tail- and mid- recursion in
 65  * the algorithm.  Also, note that <fs>_readlink() is not used in
 66  * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
 67  * may return different results than <fs>_follow_link().  Many virtual
 68  * filesystems (including /proc) exhibit this behavior.
 69  */
 70 
 71 /* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
 72  * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
 73  * and the name already exists in form of a symlink, try to create the new
 74  * name indicated by the symlink. The old code always complained that the
 75  * name already exists, due to not following the symlink even if its target
 76  * is nonexistent.  The new semantics affects also mknod() and link() when
 77  * the name is a symlink pointing to a non-existent name.
 78  *
 79  * I don't know which semantics is the right one, since I have no access
 80  * to standards. But I found by trial that HP-UX 9.0 has the full "new"
 81  * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
 82  * "old" one. Personally, I think the new semantics is much more logical.
 83  * Note that "ln old new" where "new" is a symlink pointing to a non-existing
 84  * file does succeed in both HP-UX and SunOs, but not in Solaris
 85  * and in the old Linux semantics.
 86  */
 87 
 88 /* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
 89  * semantics.  See the comments in "open_namei" and "do_link" below.
 90  *
 91  * [10-Sep-98 Alan Modra] Another symlink change.
 92  */
 93 
 94 /* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks:
 95  *      inside the path - always follow.
 96  *      in the last component in creation/removal/renaming - never follow.
 97  *      if LOOKUP_FOLLOW passed - follow.
 98  *      if the pathname has trailing slashes - follow.
 99  *      otherwise - don't follow.
100  * (applied in that order).
101  *
102  * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT
103  * restored for 2.4. This is the last surviving part of old 4.2BSD bug.
104  * During the 2.4 we need to fix the userland stuff depending on it -
105  * hopefully we will be able to get rid of that wart in 2.5. So far only
106  * XEmacs seems to be relying on it...
107  */
108 /*
109  * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland)
110  * implemented.  Let's see if raised priority of ->s_vfs_rename_mutex gives
111  * any extra contention...
112  */
113 
114 /* In order to reduce some races, while at the same time doing additional
115  * checking and hopefully speeding things up, we copy filenames to the
116  * kernel data space before using them..
117  *
118  * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
119  * PATH_MAX includes the nul terminator --RR.
120  */
121 
122 #define EMBEDDED_NAME_MAX       (PATH_MAX - offsetof(struct filename, iname))
123 
124 struct filename *
125 getname_flags(const char __user *filename, int flags, int *empty)
126 {
127         struct filename *result;
128         char *kname;
129         int len;
130 
131         result = audit_reusename(filename);
132         if (result)
133                 return result;
134 
135         result = __getname();
136         if (unlikely(!result))
137                 return ERR_PTR(-ENOMEM);
138 
139         /*
140          * First, try to embed the struct filename inside the names_cache
141          * allocation
142          */
143         kname = (char *)result->iname;
144         result->name = kname;
145 
146         len = strncpy_from_user(kname, filename, EMBEDDED_NAME_MAX);
147         if (unlikely(len < 0)) {
148                 __putname(result);
149                 return ERR_PTR(len);
150         }
151 
152         /*
153          * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a
154          * separate struct filename so we can dedicate the entire
155          * names_cache allocation for the pathname, and re-do the copy from
156          * userland.
157          */
158         if (unlikely(len == EMBEDDED_NAME_MAX)) {
159                 const size_t size = offsetof(struct filename, iname[1]);
160                 kname = (char *)result;
161 
162                 /*
163                  * size is chosen that way we to guarantee that
164                  * result->iname[0] is within the same object and that
165                  * kname can't be equal to result->iname, no matter what.
166                  */
167                 result = kzalloc(size, GFP_KERNEL);
168                 if (unlikely(!result)) {
169                         __putname(kname);
170                         return ERR_PTR(-ENOMEM);
171                 }
172                 result->name = kname;
173                 len = strncpy_from_user(kname, filename, PATH_MAX);
174                 if (unlikely(len < 0)) {
175                         __putname(kname);
176                         kfree(result);
177                         return ERR_PTR(len);
178                 }
179                 if (unlikely(len == PATH_MAX)) {
180                         __putname(kname);
181                         kfree(result);
182                         return ERR_PTR(-ENAMETOOLONG);
183                 }
184         }
185 
186         result->refcnt = 1;
187         /* The empty path is special. */
188         if (unlikely(!len)) {
189                 if (empty)
190                         *empty = 1;
191                 if (!(flags & LOOKUP_EMPTY)) {
192                         putname(result);
193                         return ERR_PTR(-ENOENT);
194                 }
195         }
196 
197         result->uptr = filename;
198         result->aname = NULL;
199         audit_getname(result);
200         return result;
201 }
202 
203 struct filename *
204 getname(const char __user * filename)
205 {
206         return getname_flags(filename, 0, NULL);
207 }
208 
209 struct filename *
210 getname_kernel(const char * filename)
211 {
212         struct filename *result;
213         int len = strlen(filename) + 1;
214 
215         result = __getname();
216         if (unlikely(!result))
217                 return ERR_PTR(-ENOMEM);
218 
219         if (len <= EMBEDDED_NAME_MAX) {
220                 result->name = (char *)result->iname;
221         } else if (len <= PATH_MAX) {
222                 struct filename *tmp;
223 
224                 tmp = kmalloc(sizeof(*tmp), GFP_KERNEL);
225                 if (unlikely(!tmp)) {
226                         __putname(result);
227                         return ERR_PTR(-ENOMEM);
228                 }
229                 tmp->name = (char *)result;
230                 result = tmp;
231         } else {
232                 __putname(result);
233                 return ERR_PTR(-ENAMETOOLONG);
234         }
235         memcpy((char *)result->name, filename, len);
236         result->uptr = NULL;
237         result->aname = NULL;
238         result->refcnt = 1;
239         audit_getname(result);
240 
241         return result;
242 }
243 
244 void putname(struct filename *name)
245 {
246         BUG_ON(name->refcnt <= 0);
247 
248         if (--name->refcnt > 0)
249                 return;
250 
251         if (name->name != name->iname) {
252                 __putname(name->name);
253                 kfree(name);
254         } else
255                 __putname(name);
256 }
257 
258 static int check_acl(struct inode *inode, int mask)
259 {
260 #ifdef CONFIG_FS_POSIX_ACL
261         struct posix_acl *acl;
262 
263         if (mask & MAY_NOT_BLOCK) {
264                 acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS);
265                 if (!acl)
266                         return -EAGAIN;
267                 /* no ->get_acl() calls in RCU mode... */
268                 if (acl == ACL_NOT_CACHED)
269                         return -ECHILD;
270                 return posix_acl_permission(inode, acl, mask & ~MAY_NOT_BLOCK);
271         }
272 
273         acl = get_acl(inode, ACL_TYPE_ACCESS);
274         if (IS_ERR(acl))
275                 return PTR_ERR(acl);
276         if (acl) {
277                 int error = posix_acl_permission(inode, acl, mask);
278                 posix_acl_release(acl);
279                 return error;
280         }
281 #endif
282 
283         return -EAGAIN;
284 }
285 
286 /*
287  * This does the basic permission checking
288  */
289 static int acl_permission_check(struct inode *inode, int mask)
290 {
291         unsigned int mode = inode->i_mode;
292 
293         if (likely(uid_eq(current_fsuid(), inode->i_uid)))
294                 mode >>= 6;
295         else {
296                 if (IS_POSIXACL(inode) && (mode & S_IRWXG)) {
297                         int error = check_acl(inode, mask);
298                         if (error != -EAGAIN)
299                                 return error;
300                 }
301 
302                 if (in_group_p(inode->i_gid))
303                         mode >>= 3;
304         }
305 
306         /*
307          * If the DACs are ok we don't need any capability check.
308          */
309         if ((mask & ~mode & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0)
310                 return 0;
311         return -EACCES;
312 }
313 
314 /**
315  * generic_permission -  check for access rights on a Posix-like filesystem
316  * @inode:      inode to check access rights for
317  * @mask:       right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, ...)
318  *
319  * Used to check for read/write/execute permissions on a file.
320  * We use "fsuid" for this, letting us set arbitrary permissions
321  * for filesystem access without changing the "normal" uids which
322  * are used for other things.
323  *
324  * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk
325  * request cannot be satisfied (eg. requires blocking or too much complexity).
326  * It would then be called again in ref-walk mode.
327  */
328 int generic_permission(struct inode *inode, int mask)
329 {
330         int ret;
331 
332         /*
333          * Do the basic permission checks.
334          */
335         ret = acl_permission_check(inode, mask);
336         if (ret != -EACCES)
337                 return ret;
338 
339         if (S_ISDIR(inode->i_mode)) {
340                 /* DACs are overridable for directories */
341                 if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
342                         return 0;
343                 if (!(mask & MAY_WRITE))
344                         if (capable_wrt_inode_uidgid(inode,
345                                                      CAP_DAC_READ_SEARCH))
346                                 return 0;
347                 return -EACCES;
348         }
349         /*
350          * Read/write DACs are always overridable.
351          * Executable DACs are overridable when there is
352          * at least one exec bit set.
353          */
354         if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
355                 if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
356                         return 0;
357 
358         /*
359          * Searching includes executable on directories, else just read.
360          */
361         mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
362         if (mask == MAY_READ)
363                 if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH))
364                         return 0;
365 
366         return -EACCES;
367 }
368 EXPORT_SYMBOL(generic_permission);
369 
370 /*
371  * We _really_ want to just do "generic_permission()" without
372  * even looking at the inode->i_op values. So we keep a cache
373  * flag in inode->i_opflags, that says "this has not special
374  * permission function, use the fast case".
375  */
376 static inline int do_inode_permission(struct inode *inode, int mask)
377 {
378         if (unlikely(!(inode->i_opflags & IOP_FASTPERM))) {
379                 if (likely(inode->i_op->permission))
380                         return inode->i_op->permission(inode, mask);
381 
382                 /* This gets set once for the inode lifetime */
383                 spin_lock(&inode->i_lock);
384                 inode->i_opflags |= IOP_FASTPERM;
385                 spin_unlock(&inode->i_lock);
386         }
387         return generic_permission(inode, mask);
388 }
389 
390 /**
391  * __inode_permission - Check for access rights to a given inode
392  * @inode: Inode to check permission on
393  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
394  *
395  * Check for read/write/execute permissions on an inode.
396  *
397  * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
398  *
399  * This does not check for a read-only file system.  You probably want
400  * inode_permission().
401  */
402 int __inode_permission(struct inode *inode, int mask)
403 {
404         int retval;
405 
406         if (unlikely(mask & MAY_WRITE)) {
407                 /*
408                  * Nobody gets write access to an immutable file.
409                  */
410                 if (IS_IMMUTABLE(inode))
411                         return -EACCES;
412         }
413 
414         retval = do_inode_permission(inode, mask);
415         if (retval)
416                 return retval;
417 
418         retval = devcgroup_inode_permission(inode, mask);
419         if (retval)
420                 return retval;
421 
422         return security_inode_permission(inode, mask);
423 }
424 EXPORT_SYMBOL(__inode_permission);
425 
426 /**
427  * sb_permission - Check superblock-level permissions
428  * @sb: Superblock of inode to check permission on
429  * @inode: Inode to check permission on
430  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
431  *
432  * Separate out file-system wide checks from inode-specific permission checks.
433  */
434 static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
435 {
436         if (unlikely(mask & MAY_WRITE)) {
437                 umode_t mode = inode->i_mode;
438 
439                 /* Nobody gets write access to a read-only fs. */
440                 if ((sb->s_flags & MS_RDONLY) &&
441                     (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
442                         return -EROFS;
443         }
444         return 0;
445 }
446 
447 /**
448  * inode_permission - Check for access rights to a given inode
449  * @inode: Inode to check permission on
450  * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
451  *
452  * Check for read/write/execute permissions on an inode.  We use fs[ug]id for
453  * this, letting us set arbitrary permissions for filesystem access without
454  * changing the "normal" UIDs which are used for other things.
455  *
456  * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
457  */
458 int inode_permission(struct inode *inode, int mask)
459 {
460         int retval;
461 
462         retval = sb_permission(inode->i_sb, inode, mask);
463         if (retval)
464                 return retval;
465         return __inode_permission(inode, mask);
466 }
467 EXPORT_SYMBOL(inode_permission);
468 
469 /**
470  * path_get - get a reference to a path
471  * @path: path to get the reference to
472  *
473  * Given a path increment the reference count to the dentry and the vfsmount.
474  */
475 void path_get(const struct path *path)
476 {
477         mntget(path->mnt);
478         dget(path->dentry);
479 }
480 EXPORT_SYMBOL(path_get);
481 
482 /**
483  * path_put - put a reference to a path
484  * @path: path to put the reference to
485  *
486  * Given a path decrement the reference count to the dentry and the vfsmount.
487  */
488 void path_put(const struct path *path)
489 {
490         dput(path->dentry);
491         mntput(path->mnt);
492 }
493 EXPORT_SYMBOL(path_put);
494 
495 #define EMBEDDED_LEVELS 2
496 struct nameidata {
497         struct path     path;
498         struct qstr     last;
499         struct path     root;
500         struct inode    *inode; /* path.dentry.d_inode */
501         unsigned int    flags;
502         unsigned        seq, m_seq;
503         int             last_type;
504         unsigned        depth;
505         int             total_link_count;
506         struct saved {
507                 struct path link;
508                 struct delayed_call done;
509                 const char *name;
510                 unsigned seq;
511         } *stack, internal[EMBEDDED_LEVELS];
512         struct filename *name;
513         struct nameidata *saved;
514         struct inode    *link_inode;
515         unsigned        root_seq;
516         int             dfd;
517 };
518 
519 static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
520 {
521         struct nameidata *old = current->nameidata;
522         p->stack = p->internal;
523         p->dfd = dfd;
524         p->name = name;
525         p->total_link_count = old ? old->total_link_count : 0;
526         p->saved = old;
527         current->nameidata = p;
528 }
529 
530 static void restore_nameidata(void)
531 {
532         struct nameidata *now = current->nameidata, *old = now->saved;
533 
534         current->nameidata = old;
535         if (old)
536                 old->total_link_count = now->total_link_count;
537         if (now->stack != now->internal)
538                 kfree(now->stack);
539 }
540 
541 static int __nd_alloc_stack(struct nameidata *nd)
542 {
543         struct saved *p;
544 
545         if (nd->flags & LOOKUP_RCU) {
546                 p= kmalloc(MAXSYMLINKS * sizeof(struct saved),
547                                   GFP_ATOMIC);
548                 if (unlikely(!p))
549                         return -ECHILD;
550         } else {
551                 p= kmalloc(MAXSYMLINKS * sizeof(struct saved),
552                                   GFP_KERNEL);
553                 if (unlikely(!p))
554                         return -ENOMEM;
555         }
556         memcpy(p, nd->internal, sizeof(nd->internal));
557         nd->stack = p;
558         return 0;
559 }
560 
561 /**
562  * path_connected - Verify that a path->dentry is below path->mnt.mnt_root
563  * @path: nameidate to verify
564  *
565  * Rename can sometimes move a file or directory outside of a bind
566  * mount, path_connected allows those cases to be detected.
567  */
568 static bool path_connected(const struct path *path)
569 {
570         struct vfsmount *mnt = path->mnt;
571 
572         /* Only bind mounts can have disconnected paths */
573         if (mnt->mnt_root == mnt->mnt_sb->s_root)
574                 return true;
575 
576         return is_subdir(path->dentry, mnt->mnt_root);
577 }
578 
579 static inline int nd_alloc_stack(struct nameidata *nd)
580 {
581         if (likely(nd->depth != EMBEDDED_LEVELS))
582                 return 0;
583         if (likely(nd->stack != nd->internal))
584                 return 0;
585         return __nd_alloc_stack(nd);
586 }
587 
588 static void drop_links(struct nameidata *nd)
589 {
590         int i = nd->depth;
591         while (i--) {
592                 struct saved *last = nd->stack + i;
593                 do_delayed_call(&last->done);
594                 clear_delayed_call(&last->done);
595         }
596 }
597 
598 static void terminate_walk(struct nameidata *nd)
599 {
600         drop_links(nd);
601         if (!(nd->flags & LOOKUP_RCU)) {
602                 int i;
603                 path_put(&nd->path);
604                 for (i = 0; i < nd->depth; i++)
605                         path_put(&nd->stack[i].link);
606                 if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
607                         path_put(&nd->root);
608                         nd->root.mnt = NULL;
609                 }
610         } else {
611                 nd->flags &= ~LOOKUP_RCU;
612                 if (!(nd->flags & LOOKUP_ROOT))
613                         nd->root.mnt = NULL;
614                 rcu_read_unlock();
615         }
616         nd->depth = 0;
617 }
618 
619 /* path_put is needed afterwards regardless of success or failure */
620 static bool legitimize_path(struct nameidata *nd,
621                             struct path *path, unsigned seq)
622 {
623         int res = __legitimize_mnt(path->mnt, nd->m_seq);
624         if (unlikely(res)) {
625                 if (res > 0)
626                         path->mnt = NULL;
627                 path->dentry = NULL;
628                 return false;
629         }
630         if (unlikely(!lockref_get_not_dead(&path->dentry->d_lockref))) {
631                 path->dentry = NULL;
632                 return false;
633         }
634         return !read_seqcount_retry(&path->dentry->d_seq, seq);
635 }
636 
637 static bool legitimize_links(struct nameidata *nd)
638 {
639         int i;
640         for (i = 0; i < nd->depth; i++) {
641                 struct saved *last = nd->stack + i;
642                 if (unlikely(!legitimize_path(nd, &last->link, last->seq))) {
643                         drop_links(nd);
644                         nd->depth = i + 1;
645                         return false;
646                 }
647         }
648         return true;
649 }
650 
651 /*
652  * Path walking has 2 modes, rcu-walk and ref-walk (see
653  * Documentation/filesystems/path-lookup.txt).  In situations when we can't
654  * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
655  * normal reference counts on dentries and vfsmounts to transition to ref-walk
656  * mode.  Refcounts are grabbed at the last known good point before rcu-walk
657  * got stuck, so ref-walk may continue from there. If this is not successful
658  * (eg. a seqcount has changed), then failure is returned and it's up to caller
659  * to restart the path walk from the beginning in ref-walk mode.
660  */
661 
662 /**
663  * unlazy_walk - try to switch to ref-walk mode.
664  * @nd: nameidata pathwalk data
665  * @dentry: child of nd->path.dentry or NULL
666  * @seq: seq number to check dentry against
667  * Returns: 0 on success, -ECHILD on failure
668  *
669  * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
670  * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
671  * @nd or NULL.  Must be called from rcu-walk context.
672  * Nothing should touch nameidata between unlazy_walk() failure and
673  * terminate_walk().
674  */
675 static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq)
676 {
677         struct dentry *parent = nd->path.dentry;
678 
679         BUG_ON(!(nd->flags & LOOKUP_RCU));
680 
681         nd->flags &= ~LOOKUP_RCU;
682         if (unlikely(!legitimize_links(nd)))
683                 goto out2;
684         if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))
685                 goto out2;
686         if (unlikely(!lockref_get_not_dead(&parent->d_lockref)))
687                 goto out1;
688 
689         /*
690          * For a negative lookup, the lookup sequence point is the parents
691          * sequence point, and it only needs to revalidate the parent dentry.
692          *
693          * For a positive lookup, we need to move both the parent and the
694          * dentry from the RCU domain to be properly refcounted. And the
695          * sequence number in the dentry validates *both* dentry counters,
696          * since we checked the sequence number of the parent after we got
697          * the child sequence number. So we know the parent must still
698          * be valid if the child sequence number is still valid.
699          */
700         if (!dentry) {
701                 if (read_seqcount_retry(&parent->d_seq, nd->seq))
702                         goto out;
703                 BUG_ON(nd->inode != parent->d_inode);
704         } else {
705                 if (!lockref_get_not_dead(&dentry->d_lockref))
706                         goto out;
707                 if (read_seqcount_retry(&dentry->d_seq, seq))
708                         goto drop_dentry;
709         }
710 
711         /*
712          * Sequence counts matched. Now make sure that the root is
713          * still valid and get it if required.
714          */
715         if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
716                 if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq))) {
717                         rcu_read_unlock();
718                         dput(dentry);
719                         return -ECHILD;
720                 }
721         }
722 
723         rcu_read_unlock();
724         return 0;
725 
726 drop_dentry:
727         rcu_read_unlock();
728         dput(dentry);
729         goto drop_root_mnt;
730 out2:
731         nd->path.mnt = NULL;
732 out1:
733         nd->path.dentry = NULL;
734 out:
735         rcu_read_unlock();
736 drop_root_mnt:
737         if (!(nd->flags & LOOKUP_ROOT))
738                 nd->root.mnt = NULL;
739         return -ECHILD;
740 }
741 
742 static int unlazy_link(struct nameidata *nd, struct path *link, unsigned seq)
743 {
744         if (unlikely(!legitimize_path(nd, link, seq))) {
745                 drop_links(nd);
746                 nd->depth = 0;
747                 nd->flags &= ~LOOKUP_RCU;
748                 nd->path.mnt = NULL;
749                 nd->path.dentry = NULL;
750                 if (!(nd->flags & LOOKUP_ROOT))
751                         nd->root.mnt = NULL;
752                 rcu_read_unlock();
753         } else if (likely(unlazy_walk(nd, NULL, 0)) == 0) {
754                 return 0;
755         }
756         path_put(link);
757         return -ECHILD;
758 }
759 
760 static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
761 {
762         return dentry->d_op->d_revalidate(dentry, flags);
763 }
764 
765 /**
766  * complete_walk - successful completion of path walk
767  * @nd:  pointer nameidata
768  *
769  * If we had been in RCU mode, drop out of it and legitimize nd->path.
770  * Revalidate the final result, unless we'd already done that during
771  * the path walk or the filesystem doesn't ask for it.  Return 0 on
772  * success, -error on failure.  In case of failure caller does not
773  * need to drop nd->path.
774  */
775 static int complete_walk(struct nameidata *nd)
776 {
777         struct dentry *dentry = nd->path.dentry;
778         int status;
779 
780         if (nd->flags & LOOKUP_RCU) {
781                 if (!(nd->flags & LOOKUP_ROOT))
782                         nd->root.mnt = NULL;
783                 if (unlikely(unlazy_walk(nd, NULL, 0)))
784                         return -ECHILD;
785         }
786 
787         if (likely(!(nd->flags & LOOKUP_JUMPED)))
788                 return 0;
789 
790         if (likely(!(dentry->d_flags & DCACHE_OP_WEAK_REVALIDATE)))
791                 return 0;
792 
793         status = dentry->d_op->d_weak_revalidate(dentry, nd->flags);
794         if (status > 0)
795                 return 0;
796 
797         if (!status)
798                 status = -ESTALE;
799 
800         return status;
801 }
802 
803 static void set_root(struct nameidata *nd)
804 {
805         struct fs_struct *fs = current->fs;
806 
807         if (nd->flags & LOOKUP_RCU) {
808                 unsigned seq;
809 
810                 do {
811                         seq = read_seqcount_begin(&fs->seq);
812                         nd->root = fs->root;
813                         nd->root_seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
814                 } while (read_seqcount_retry(&fs->seq, seq));
815         } else {
816                 get_fs_root(fs, &nd->root);
817         }
818 }
819 
820 static void path_put_conditional(struct path *path, struct nameidata *nd)
821 {
822         dput(path->dentry);
823         if (path->mnt != nd->path.mnt)
824                 mntput(path->mnt);
825 }
826 
827 static inline void path_to_nameidata(const struct path *path,
828                                         struct nameidata *nd)
829 {
830         if (!(nd->flags & LOOKUP_RCU)) {
831                 dput(nd->path.dentry);
832                 if (nd->path.mnt != path->mnt)
833                         mntput(nd->path.mnt);
834         }
835         nd->path.mnt = path->mnt;
836         nd->path.dentry = path->dentry;
837 }
838 
839 static int nd_jump_root(struct nameidata *nd)
840 {
841         if (nd->flags & LOOKUP_RCU) {
842                 struct dentry *d;
843                 nd->path = nd->root;
844                 d = nd->path.dentry;
845                 nd->inode = d->d_inode;
846                 nd->seq = nd->root_seq;
847                 if (unlikely(read_seqcount_retry(&d->d_seq, nd->seq)))
848                         return -ECHILD;
849         } else {
850                 path_put(&nd->path);
851                 nd->path = nd->root;
852                 path_get(&nd->path);
853                 nd->inode = nd->path.dentry->d_inode;
854         }
855         nd->flags |= LOOKUP_JUMPED;
856         return 0;
857 }
858 
859 /*
860  * Helper to directly jump to a known parsed path from ->get_link,
861  * caller must have taken a reference to path beforehand.
862  */
863 void nd_jump_link(struct path *path)
864 {
865         struct nameidata *nd = current->nameidata;
866         path_put(&nd->path);
867 
868         nd->path = *path;
869         nd->inode = nd->path.dentry->d_inode;
870         nd->flags |= LOOKUP_JUMPED;
871 }
872 
873 static inline void put_link(struct nameidata *nd)
874 {
875         struct saved *last = nd->stack + --nd->depth;
876         do_delayed_call(&last->done);
877         if (!(nd->flags & LOOKUP_RCU))
878                 path_put(&last->link);
879 }
880 
881 int sysctl_protected_symlinks __read_mostly = 0;
882 int sysctl_protected_hardlinks __read_mostly = 0;
883 
884 /**
885  * may_follow_link - Check symlink following for unsafe situations
886  * @nd: nameidata pathwalk data
887  *
888  * In the case of the sysctl_protected_symlinks sysctl being enabled,
889  * CAP_DAC_OVERRIDE needs to be specifically ignored if the symlink is
890  * in a sticky world-writable directory. This is to protect privileged
891  * processes from failing races against path names that may change out
892  * from under them by way of other users creating malicious symlinks.
893  * It will permit symlinks to be followed only when outside a sticky
894  * world-writable directory, or when the uid of the symlink and follower
895  * match, or when the directory owner matches the symlink's owner.
896  *
897  * Returns 0 if following the symlink is allowed, -ve on error.
898  */
899 static inline int may_follow_link(struct nameidata *nd)
900 {
901         const struct inode *inode;
902         const struct inode *parent;
903 
904         if (!sysctl_protected_symlinks)
905                 return 0;
906 
907         /* Allowed if owner and follower match. */
908         inode = nd->link_inode;
909         if (uid_eq(current_cred()->fsuid, inode->i_uid))
910                 return 0;
911 
912         /* Allowed if parent directory not sticky and world-writable. */
913         parent = nd->inode;
914         if ((parent->i_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH))
915                 return 0;
916 
917         /* Allowed if parent directory and link owner match. */
918         if (uid_eq(parent->i_uid, inode->i_uid))
919                 return 0;
920 
921         if (nd->flags & LOOKUP_RCU)
922                 return -ECHILD;
923 
924         audit_log_link_denied("follow_link", &nd->stack[0].link);
925         return -EACCES;
926 }
927 
928 /**
929  * safe_hardlink_source - Check for safe hardlink conditions
930  * @inode: the source inode to hardlink from
931  *
932  * Return false if at least one of the following conditions:
933  *    - inode is not a regular file
934  *    - inode is setuid
935  *    - inode is setgid and group-exec
936  *    - access failure for read and write
937  *
938  * Otherwise returns true.
939  */
940 static bool safe_hardlink_source(struct inode *inode)
941 {
942         umode_t mode = inode->i_mode;
943 
944         /* Special files should not get pinned to the filesystem. */
945         if (!S_ISREG(mode))
946                 return false;
947 
948         /* Setuid files should not get pinned to the filesystem. */
949         if (mode & S_ISUID)
950                 return false;
951 
952         /* Executable setgid files should not get pinned to the filesystem. */
953         if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
954                 return false;
955 
956         /* Hardlinking to unreadable or unwritable sources is dangerous. */
957         if (inode_permission(inode, MAY_READ | MAY_WRITE))
958                 return false;
959 
960         return true;
961 }
962 
963 /**
964  * may_linkat - Check permissions for creating a hardlink
965  * @link: the source to hardlink from
966  *
967  * Block hardlink when all of:
968  *  - sysctl_protected_hardlinks enabled
969  *  - fsuid does not match inode
970  *  - hardlink source is unsafe (see safe_hardlink_source() above)
971  *  - not CAP_FOWNER in a namespace with the inode owner uid mapped
972  *
973  * Returns 0 if successful, -ve on error.
974  */
975 static int may_linkat(struct path *link)
976 {
977         struct inode *inode;
978 
979         if (!sysctl_protected_hardlinks)
980                 return 0;
981 
982         inode = link->dentry->d_inode;
983 
984         /* Source inode owner (or CAP_FOWNER) can hardlink all they like,
985          * otherwise, it must be a safe source.
986          */
987         if (inode_owner_or_capable(inode) || safe_hardlink_source(inode))
988                 return 0;
989 
990         audit_log_link_denied("linkat", link);
991         return -EPERM;
992 }
993 
994 static __always_inline
995 const char *get_link(struct nameidata *nd)
996 {
997         struct saved *last = nd->stack + nd->depth - 1;
998         struct dentry *dentry = last->link.dentry;
999         struct inode *inode = nd->link_inode;
1000         int error;
1001         const char *res;
1002 
1003         if (!(nd->flags & LOOKUP_RCU)) {
1004                 touch_atime(&last->link);
1005                 cond_resched();
1006         } else if (atime_needs_update(&last->link, inode)) {
1007                 if (unlikely(unlazy_walk(nd, NULL, 0)))
1008                         return ERR_PTR(-ECHILD);
1009                 touch_atime(&last->link);
1010         }
1011 
1012         error = security_inode_follow_link(dentry, inode,
1013                                            nd->flags & LOOKUP_RCU);
1014         if (unlikely(error))
1015                 return ERR_PTR(error);
1016 
1017         nd->last_type = LAST_BIND;
1018         res = inode->i_link;
1019         if (!res) {
1020                 const char * (*get)(struct dentry *, struct inode *,
1021                                 struct delayed_call *);
1022                 get = inode->i_op->get_link;
1023                 if (nd->flags & LOOKUP_RCU) {
1024                         res = get(NULL, inode, &last->done);
1025                         if (res == ERR_PTR(-ECHILD)) {
1026                                 if (unlikely(unlazy_walk(nd, NULL, 0)))
1027                                         return ERR_PTR(-ECHILD);
1028                                 res = get(dentry, inode, &last->done);
1029                         }
1030                 } else {
1031                         res = get(dentry, inode, &last->done);
1032                 }
1033                 if (IS_ERR_OR_NULL(res))
1034                         return res;
1035         }
1036         if (*res == '/') {
1037                 if (!nd->root.mnt)
1038                         set_root(nd);
1039                 if (unlikely(nd_jump_root(nd)))
1040                         return ERR_PTR(-ECHILD);
1041                 while (unlikely(*++res == '/'))
1042                         ;
1043         }
1044         if (!*res)
1045                 res = NULL;
1046         return res;
1047 }
1048 
1049 /*
1050  * follow_up - Find the mountpoint of path's vfsmount
1051  *
1052  * Given a path, find the mountpoint of its source file system.
1053  * Replace @path with the path of the mountpoint in the parent mount.
1054  * Up is towards /.
1055  *
1056  * Return 1 if we went up a level and 0 if we were already at the
1057  * root.
1058  */
1059 int follow_up(struct path *path)
1060 {
1061         struct mount *mnt = real_mount(path->mnt);
1062         struct mount *parent;
1063         struct dentry *mountpoint;
1064 
1065         read_seqlock_excl(&mount_lock);
1066         parent = mnt->mnt_parent;
1067         if (parent == mnt) {
1068                 read_sequnlock_excl(&mount_lock);
1069                 return 0;
1070         }
1071         mntget(&parent->mnt);
1072         mountpoint = dget(mnt->mnt_mountpoint);
1073         read_sequnlock_excl(&mount_lock);
1074         dput(path->dentry);
1075         path->dentry = mountpoint;
1076         mntput(path->mnt);
1077         path->mnt = &parent->mnt;
1078         return 1;
1079 }
1080 EXPORT_SYMBOL(follow_up);
1081 
1082 /*
1083  * Perform an automount
1084  * - return -EISDIR to tell follow_managed() to stop and return the path we
1085  *   were called with.
1086  */
1087 static int follow_automount(struct path *path, struct nameidata *nd,
1088                             bool *need_mntput)
1089 {
1090         struct vfsmount *mnt;
1091         int err;
1092 
1093         if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
1094                 return -EREMOTE;
1095 
1096         /* We don't want to mount if someone's just doing a stat -
1097          * unless they're stat'ing a directory and appended a '/' to
1098          * the name.
1099          *
1100          * We do, however, want to mount if someone wants to open or
1101          * create a file of any type under the mountpoint, wants to
1102          * traverse through the mountpoint or wants to open the
1103          * mounted directory.  Also, autofs may mark negative dentries
1104          * as being automount points.  These will need the attentions
1105          * of the daemon to instantiate them before they can be used.
1106          */
1107         if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
1108                            LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
1109             path->dentry->d_inode)
1110                 return -EISDIR;
1111 
1112         nd->total_link_count++;
1113         if (nd->total_link_count >= 40)
1114                 return -ELOOP;
1115 
1116         mnt = path->dentry->d_op->d_automount(path);
1117         if (IS_ERR(mnt)) {
1118                 /*
1119                  * The filesystem is allowed to return -EISDIR here to indicate
1120                  * it doesn't want to automount.  For instance, autofs would do
1121                  * this so that its userspace daemon can mount on this dentry.
1122                  *
1123                  * However, we can only permit this if it's a terminal point in
1124                  * the path being looked up; if it wasn't then the remainder of
1125                  * the path is inaccessible and we should say so.
1126                  */
1127                 if (PTR_ERR(mnt) == -EISDIR && (nd->flags & LOOKUP_PARENT))
1128                         return -EREMOTE;
1129                 return PTR_ERR(mnt);
1130         }
1131 
1132         if (!mnt) /* mount collision */
1133                 return 0;
1134 
1135         if (!*need_mntput) {
1136                 /* lock_mount() may release path->mnt on error */
1137                 mntget(path->mnt);
1138                 *need_mntput = true;
1139         }
1140         err = finish_automount(mnt, path);
1141 
1142         switch (err) {
1143         case -EBUSY:
1144                 /* Someone else made a mount here whilst we were busy */
1145                 return 0;
1146         case 0:
1147                 path_put(path);
1148                 path->mnt = mnt;
1149                 path->dentry = dget(mnt->mnt_root);
1150                 return 0;
1151         default:
1152                 return err;
1153         }
1154 
1155 }
1156 
1157 /*
1158  * Handle a dentry that is managed in some way.
1159  * - Flagged for transit management (autofs)
1160  * - Flagged as mountpoint
1161  * - Flagged as automount point
1162  *
1163  * This may only be called in refwalk mode.
1164  *
1165  * Serialization is taken care of in namespace.c
1166  */
1167 static int follow_managed(struct path *path, struct nameidata *nd)
1168 {
1169         struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */
1170         unsigned managed;
1171         bool need_mntput = false;
1172         int ret = 0;
1173 
1174         /* Given that we're not holding a lock here, we retain the value in a
1175          * local variable for each dentry as we look at it so that we don't see
1176          * the components of that value change under us */
1177         while (managed = ACCESS_ONCE(path->dentry->d_flags),
1178                managed &= DCACHE_MANAGED_DENTRY,
1179                unlikely(managed != 0)) {
1180                 /* Allow the filesystem to manage the transit without i_mutex
1181                  * being held. */
1182                 if (managed & DCACHE_MANAGE_TRANSIT) {
1183                         BUG_ON(!path->dentry->d_op);
1184                         BUG_ON(!path->dentry->d_op->d_manage);
1185                         ret = path->dentry->d_op->d_manage(path->dentry, false);
1186                         if (ret < 0)
1187                                 break;
1188                 }
1189 
1190                 /* Transit to a mounted filesystem. */
1191                 if (managed & DCACHE_MOUNTED) {
1192                         struct vfsmount *mounted = lookup_mnt(path);
1193                         if (mounted) {
1194                                 dput(path->dentry);
1195                                 if (need_mntput)
1196                                         mntput(path->mnt);
1197                                 path->mnt = mounted;
1198                                 path->dentry = dget(mounted->mnt_root);
1199                                 need_mntput = true;
1200                                 continue;
1201                         }
1202 
1203                         /* Something is mounted on this dentry in another
1204                          * namespace and/or whatever was mounted there in this
1205                          * namespace got unmounted before lookup_mnt() could
1206                          * get it */
1207                 }
1208 
1209                 /* Handle an automount point */
1210                 if (managed & DCACHE_NEED_AUTOMOUNT) {
1211                         ret = follow_automount(path, nd, &need_mntput);
1212                         if (ret < 0)
1213                                 break;
1214                         continue;
1215                 }
1216 
1217                 /* We didn't change the current path point */
1218                 break;
1219         }
1220 
1221         if (need_mntput && path->mnt == mnt)
1222                 mntput(path->mnt);
1223         if (ret == -EISDIR || !ret)
1224                 ret = 1;
1225         if (need_mntput)
1226                 nd->flags |= LOOKUP_JUMPED;
1227         if (unlikely(ret < 0))
1228                 path_put_conditional(path, nd);
1229         return ret;
1230 }
1231 
1232 int follow_down_one(struct path *path)
1233 {
1234         struct vfsmount *mounted;
1235 
1236         mounted = lookup_mnt(path);
1237         if (mounted) {
1238                 dput(path->dentry);
1239                 mntput(path->mnt);
1240                 path->mnt = mounted;
1241                 path->dentry = dget(mounted->mnt_root);
1242                 return 1;
1243         }
1244         return 0;
1245 }
1246 EXPORT_SYMBOL(follow_down_one);
1247 
1248 static inline int managed_dentry_rcu(struct dentry *dentry)
1249 {
1250         return (dentry->d_flags & DCACHE_MANAGE_TRANSIT) ?
1251                 dentry->d_op->d_manage(dentry, true) : 0;
1252 }
1253 
1254 /*
1255  * Try to skip to top of mountpoint pile in rcuwalk mode.  Fail if
1256  * we meet a managed dentry that would need blocking.
1257  */
1258 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
1259                                struct inode **inode, unsigned *seqp)
1260 {
1261         for (;;) {
1262                 struct mount *mounted;
1263                 /*
1264                  * Don't forget we might have a non-mountpoint managed dentry
1265                  * that wants to block transit.
1266                  */
1267                 switch (managed_dentry_rcu(path->dentry)) {
1268                 case -ECHILD:
1269                 default:
1270                         return false;
1271                 case -EISDIR:
1272                         return true;
1273                 case 0:
1274                         break;
1275                 }
1276 
1277                 if (!d_mountpoint(path->dentry))
1278                         return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
1279 
1280                 mounted = __lookup_mnt(path->mnt, path->dentry);
1281                 if (!mounted)
1282                         break;
1283                 path->mnt = &mounted->mnt;
1284                 path->dentry = mounted->mnt.mnt_root;
1285                 nd->flags |= LOOKUP_JUMPED;
1286                 *seqp = read_seqcount_begin(&path->dentry->d_seq);
1287                 /*
1288                  * Update the inode too. We don't need to re-check the
1289                  * dentry sequence number here after this d_inode read,
1290                  * because a mount-point is always pinned.
1291                  */
1292                 *inode = path->dentry->d_inode;
1293         }
1294         return !read_seqretry(&mount_lock, nd->m_seq) &&
1295                 !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
1296 }
1297 
1298 static int follow_dotdot_rcu(struct nameidata *nd)
1299 {
1300         struct inode *inode = nd->inode;
1301 
1302         while (1) {
1303                 if (path_equal(&nd->path, &nd->root))
1304                         break;
1305                 if (nd->path.dentry != nd->path.mnt->mnt_root) {
1306                         struct dentry *old = nd->path.dentry;
1307                         struct dentry *parent = old->d_parent;
1308                         unsigned seq;
1309 
1310                         inode = parent->d_inode;
1311                         seq = read_seqcount_begin(&parent->d_seq);
1312                         if (unlikely(read_seqcount_retry(&old->d_seq, nd->seq)))
1313                                 return -ECHILD;
1314                         nd->path.dentry = parent;
1315                         nd->seq = seq;
1316                         if (unlikely(!path_connected(&nd->path)))
1317                                 return -ENOENT;
1318                         break;
1319                 } else {
1320                         struct mount *mnt = real_mount(nd->path.mnt);
1321                         struct mount *mparent = mnt->mnt_parent;
1322                         struct dentry *mountpoint = mnt->mnt_mountpoint;
1323                         struct inode *inode2 = mountpoint->d_inode;
1324                         unsigned seq = read_seqcount_begin(&mountpoint->d_seq);
1325                         if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
1326                                 return -ECHILD;
1327                         if (&mparent->mnt == nd->path.mnt)
1328                                 break;
1329                         /* we know that mountpoint was pinned */
1330                         nd->path.dentry = mountpoint;
1331                         nd->path.mnt = &mparent->mnt;
1332                         inode = inode2;
1333                         nd->seq = seq;
1334                 }
1335         }
1336         while (unlikely(d_mountpoint(nd->path.dentry))) {
1337                 struct mount *mounted;
1338                 mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry);
1339                 if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
1340                         return -ECHILD;
1341                 if (!mounted)
1342                         break;
1343                 nd->path.mnt = &mounted->mnt;
1344                 nd->path.dentry = mounted->mnt.mnt_root;
1345                 inode = nd->path.dentry->d_inode;
1346                 nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
1347         }
1348         nd->inode = inode;
1349         return 0;
1350 }
1351 
1352 /*
1353  * Follow down to the covering mount currently visible to userspace.  At each
1354  * point, the filesystem owning that dentry may be queried as to whether the
1355  * caller is permitted to proceed or not.
1356  */
1357 int follow_down(struct path *path)
1358 {
1359         unsigned managed;
1360         int ret;
1361 
1362         while (managed = ACCESS_ONCE(path->dentry->d_flags),
1363                unlikely(managed & DCACHE_MANAGED_DENTRY)) {
1364                 /* Allow the filesystem to manage the transit without i_mutex
1365                  * being held.
1366                  *
1367                  * We indicate to the filesystem if someone is trying to mount
1368                  * something here.  This gives autofs the chance to deny anyone
1369                  * other than its daemon the right to mount on its
1370                  * superstructure.
1371                  *
1372                  * The filesystem may sleep at this point.
1373                  */
1374                 if (managed & DCACHE_MANAGE_TRANSIT) {
1375                         BUG_ON(!path->dentry->d_op);
1376                         BUG_ON(!path->dentry->d_op->d_manage);
1377                         ret = path->dentry->d_op->d_manage(
1378                                 path->dentry, false);
1379                         if (ret < 0)
1380                                 return ret == -EISDIR ? 0 : ret;
1381                 }
1382 
1383                 /* Transit to a mounted filesystem. */
1384                 if (managed & DCACHE_MOUNTED) {
1385                         struct vfsmount *mounted = lookup_mnt(path);
1386                         if (!mounted)
1387                                 break;
1388                         dput(path->dentry);
1389                         mntput(path->mnt);
1390                         path->mnt = mounted;
1391                         path->dentry = dget(mounted->mnt_root);
1392                         continue;
1393                 }
1394 
1395                 /* Don't handle automount points here */
1396                 break;
1397         }
1398         return 0;
1399 }
1400 EXPORT_SYMBOL(follow_down);
1401 
1402 /*
1403  * Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
1404  */
1405 static void follow_mount(struct path *path)
1406 {
1407         while (d_mountpoint(path->dentry)) {
1408                 struct vfsmount *mounted = lookup_mnt(path);
1409                 if (!mounted)
1410                         break;
1411                 dput(path->dentry);
1412                 mntput(path->mnt);
1413                 path->mnt = mounted;
1414                 path->dentry = dget(mounted->mnt_root);
1415         }
1416 }
1417 
1418 static int follow_dotdot(struct nameidata *nd)
1419 {
1420         while(1) {
1421                 struct dentry *old = nd->path.dentry;
1422 
1423                 if (nd->path.dentry == nd->root.dentry &&
1424                     nd->path.mnt == nd->root.mnt) {
1425                         break;
1426                 }
1427                 if (nd->path.dentry != nd->path.mnt->mnt_root) {
1428                         /* rare case of legitimate dget_parent()... */
1429                         nd->path.dentry = dget_parent(nd->path.dentry);
1430                         dput(old);
1431                         if (unlikely(!path_connected(&nd->path)))
1432                                 return -ENOENT;
1433                         break;
1434                 }
1435                 if (!follow_up(&nd->path))
1436                         break;
1437         }
1438         follow_mount(&nd->path);
1439         nd->inode = nd->path.dentry->d_inode;
1440         return 0;
1441 }
1442 
1443 /*
1444  * This looks up the name in dcache, possibly revalidates the old dentry and
1445  * allocates a new one if not found or not valid.  In the need_lookup argument
1446  * returns whether i_op->lookup is necessary.
1447  */
1448 static struct dentry *lookup_dcache(const struct qstr *name,
1449                                     struct dentry *dir,
1450                                     unsigned int flags)
1451 {
1452         struct dentry *dentry;
1453         int error;
1454 
1455         dentry = d_lookup(dir, name);
1456         if (dentry) {
1457                 if (dentry->d_flags & DCACHE_OP_REVALIDATE) {
1458                         error = d_revalidate(dentry, flags);
1459                         if (unlikely(error <= 0)) {
1460                                 if (!error)
1461                                         d_invalidate(dentry);
1462                                 dput(dentry);
1463                                 return ERR_PTR(error);
1464                         }
1465                 }
1466         }
1467         return dentry;
1468 }
1469 
1470 /*
1471  * Call i_op->lookup on the dentry.  The dentry must be negative and
1472  * unhashed.
1473  *
1474  * dir->d_inode->i_mutex must be held
1475  */
1476 static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry,
1477                                   unsigned int flags)
1478 {
1479         struct dentry *old;
1480 
1481         /* Don't create child dentry for a dead directory. */
1482         if (unlikely(IS_DEADDIR(dir))) {
1483                 dput(dentry);
1484                 return ERR_PTR(-ENOENT);
1485         }
1486 
1487         old = dir->i_op->lookup(dir, dentry, flags);
1488         if (unlikely(old)) {
1489                 dput(dentry);
1490                 dentry = old;
1491         }
1492         return dentry;
1493 }
1494 
1495 static struct dentry *__lookup_hash(const struct qstr *name,
1496                 struct dentry *base, unsigned int flags)
1497 {
1498         struct dentry *dentry = lookup_dcache(name, base, flags);
1499 
1500         if (dentry)
1501                 return dentry;
1502 
1503         dentry = d_alloc(base, name);
1504         if (unlikely(!dentry))
1505                 return ERR_PTR(-ENOMEM);
1506 
1507         return lookup_real(base->d_inode, dentry, flags);
1508 }
1509 
1510 static int lookup_fast(struct nameidata *nd,
1511                        struct path *path, struct inode **inode,
1512                        unsigned *seqp)
1513 {
1514         struct vfsmount *mnt = nd->path.mnt;
1515         struct dentry *dentry, *parent = nd->path.dentry;
1516         int status = 1;
1517         int err;
1518 
1519         /*
1520          * Rename seqlock is not required here because in the off chance
1521          * of a false negative due to a concurrent rename, the caller is
1522          * going to fall back to non-racy lookup.
1523          */
1524         if (nd->flags & LOOKUP_RCU) {
1525                 unsigned seq;
1526                 bool negative;
1527                 dentry = __d_lookup_rcu(parent, &nd->last, &seq);
1528                 if (unlikely(!dentry)) {
1529                         if (unlazy_walk(nd, NULL, 0))
1530                                 return -ECHILD;
1531                         return 0;
1532                 }
1533 
1534                 /*
1535                  * This sequence count validates that the inode matches
1536                  * the dentry name information from lookup.
1537                  */
1538                 *inode = d_backing_inode(dentry);
1539                 negative = d_is_negative(dentry);
1540                 if (unlikely(read_seqcount_retry(&dentry->d_seq, seq)))
1541                         return -ECHILD;
1542 
1543                 /*
1544                  * This sequence count validates that the parent had no
1545                  * changes while we did the lookup of the dentry above.
1546                  *
1547                  * The memory barrier in read_seqcount_begin of child is
1548                  *  enough, we can use __read_seqcount_retry here.
1549                  */
1550                 if (unlikely(__read_seqcount_retry(&parent->d_seq, nd->seq)))
1551                         return -ECHILD;
1552 
1553                 *seqp = seq;
1554                 if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
1555                         status = d_revalidate(dentry, nd->flags);
1556                 if (unlikely(status <= 0)) {
1557                         if (unlazy_walk(nd, dentry, seq))
1558                                 return -ECHILD;
1559                         if (status == -ECHILD)
1560                                 status = d_revalidate(dentry, nd->flags);
1561                 } else {
1562                         /*
1563                          * Note: do negative dentry check after revalidation in
1564                          * case that drops it.
1565                          */
1566                         if (unlikely(negative))
1567                                 return -ENOENT;
1568                         path->mnt = mnt;
1569                         path->dentry = dentry;
1570                         if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
1571                                 return 1;
1572                         if (unlazy_walk(nd, dentry, seq))
1573                                 return -ECHILD;
1574                 }
1575         } else {
1576                 dentry = __d_lookup(parent, &nd->last);
1577                 if (unlikely(!dentry))
1578                         return 0;
1579                 if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE))
1580                         status = d_revalidate(dentry, nd->flags);
1581         }
1582         if (unlikely(status <= 0)) {
1583                 if (!status)
1584                         d_invalidate(dentry);
1585                 dput(dentry);
1586                 return status;
1587         }
1588         if (unlikely(d_is_negative(dentry))) {
1589                 dput(dentry);
1590                 return -ENOENT;
1591         }
1592 
1593         path->mnt = mnt;
1594         path->dentry = dentry;
1595         err = follow_managed(path, nd);
1596         if (likely(err > 0))
1597                 *inode = d_backing_inode(path->dentry);
1598         return err;
1599 }
1600 
1601 /* Fast lookup failed, do it the slow way */
1602 static struct dentry *lookup_slow(const struct qstr *name,
1603                                   struct dentry *dir,
1604                                   unsigned int flags)
1605 {
1606         struct dentry *dentry;
1607         inode_lock(dir->d_inode);
1608         dentry = d_lookup(dir, name);
1609         if (unlikely(dentry)) {
1610                 if ((dentry->d_flags & DCACHE_OP_REVALIDATE) &&
1611                     !(flags & LOOKUP_NO_REVAL)) {
1612                         int error = d_revalidate(dentry, flags);
1613                         if (unlikely(error <= 0)) {
1614                                 if (!error)
1615                                         d_invalidate(dentry);
1616                                 dput(dentry);
1617                                 dentry = ERR_PTR(error);
1618                         }
1619                 }
1620                 if (dentry) {
1621                         inode_unlock(dir->d_inode);
1622                         return dentry;
1623                 }
1624         }
1625         dentry = d_alloc(dir, name);
1626         if (unlikely(!dentry)) {
1627                 inode_unlock(dir->d_inode);
1628                 return ERR_PTR(-ENOMEM);
1629         }
1630         dentry = lookup_real(dir->d_inode, dentry, flags);
1631         inode_unlock(dir->d_inode);
1632         return dentry;
1633 }
1634 
1635 static inline int may_lookup(struct nameidata *nd)
1636 {
1637         if (nd->flags & LOOKUP_RCU) {
1638                 int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
1639                 if (err != -ECHILD)
1640                         return err;
1641                 if (unlazy_walk(nd, NULL, 0))
1642                         return -ECHILD;
1643         }
1644         return inode_permission(nd->inode, MAY_EXEC);
1645 }
1646 
1647 static inline int handle_dots(struct nameidata *nd, int type)
1648 {
1649         if (type == LAST_DOTDOT) {
1650                 if (!nd->root.mnt)
1651                         set_root(nd);
1652                 if (nd->flags & LOOKUP_RCU) {
1653                         return follow_dotdot_rcu(nd);
1654                 } else
1655                         return follow_dotdot(nd);
1656         }
1657         return 0;
1658 }
1659 
1660 static int pick_link(struct nameidata *nd, struct path *link,
1661                      struct inode *inode, unsigned seq)
1662 {
1663         int error;
1664         struct saved *last;
1665         if (unlikely(nd->total_link_count++ >= MAXSYMLINKS)) {
1666                 path_to_nameidata(link, nd);
1667                 return -ELOOP;
1668         }
1669         if (!(nd->flags & LOOKUP_RCU)) {
1670                 if (link->mnt == nd->path.mnt)
1671                         mntget(link->mnt);
1672         }
1673         error = nd_alloc_stack(nd);
1674         if (unlikely(error)) {
1675                 if (error == -ECHILD) {
1676                         if (unlikely(unlazy_link(nd, link, seq)))
1677                                 return -ECHILD;
1678                         error = nd_alloc_stack(nd);
1679                 }
1680                 if (error) {
1681                         path_put(link);
1682                         return error;
1683                 }
1684         }
1685 
1686         last = nd->stack + nd->depth++;
1687         last->link = *link;
1688         clear_delayed_call(&last->done);
1689         nd->link_inode = inode;
1690         last->seq = seq;
1691         return 1;
1692 }
1693 
1694 /*
1695  * Do we need to follow links? We _really_ want to be able
1696  * to do this check without having to look at inode->i_op,
1697  * so we keep a cache of "no, this doesn't need follow_link"
1698  * for the common case.
1699  */
1700 static inline int should_follow_link(struct nameidata *nd, struct path *link,
1701                                      int follow,
1702                                      struct inode *inode, unsigned seq)
1703 {
1704         if (likely(!d_is_symlink(link->dentry)))
1705                 return 0;
1706         if (!follow)
1707                 return 0;
1708         /* make sure that d_is_symlink above matches inode */
1709         if (nd->flags & LOOKUP_RCU) {
1710                 if (read_seqcount_retry(&link->dentry->d_seq, seq))
1711                         return -ECHILD;
1712         }
1713         return pick_link(nd, link, inode, seq);
1714 }
1715 
1716 enum {WALK_GET = 1, WALK_PUT = 2};
1717 
1718 static int walk_component(struct nameidata *nd, int flags)
1719 {
1720         struct path path;
1721         struct inode *inode;
1722         unsigned seq;
1723         int err;
1724         /*
1725          * "." and ".." are special - ".." especially so because it has
1726          * to be able to know about the current root directory and
1727          * parent relationships.
1728          */
1729         if (unlikely(nd->last_type != LAST_NORM)) {
1730                 err = handle_dots(nd, nd->last_type);
1731                 if (flags & WALK_PUT)
1732                         put_link(nd);
1733                 return err;
1734         }
1735         err = lookup_fast(nd, &path, &inode, &seq);
1736         if (unlikely(err <= 0)) {
1737                 if (err < 0)
1738                         return err;
1739                 path.dentry = lookup_slow(&nd->last, nd->path.dentry,
1740                                           nd->flags);
1741                 if (IS_ERR(path.dentry))
1742                         return PTR_ERR(path.dentry);
1743 
1744                 path.mnt = nd->path.mnt;
1745                 err = follow_managed(&path, nd);
1746                 if (unlikely(err < 0))
1747                         return err;
1748 
1749                 if (unlikely(d_is_negative(path.dentry))) {
1750                         path_to_nameidata(&path, nd);
1751                         return -ENOENT;
1752                 }
1753 
1754                 seq = 0;        /* we are already out of RCU mode */
1755                 inode = d_backing_inode(path.dentry);
1756         }
1757 
1758         if (flags & WALK_PUT)
1759                 put_link(nd);
1760         err = should_follow_link(nd, &path, flags & WALK_GET, inode, seq);
1761         if (unlikely(err))
1762                 return err;
1763         path_to_nameidata(&path, nd);
1764         nd->inode = inode;
1765         nd->seq = seq;
1766         return 0;
1767 }
1768 
1769 /*
1770  * We can do the critical dentry name comparison and hashing
1771  * operations one word at a time, but we are limited to:
1772  *
1773  * - Architectures with fast unaligned word accesses. We could
1774  *   do a "get_unaligned()" if this helps and is sufficiently
1775  *   fast.
1776  *
1777  * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we
1778  *   do not trap on the (extremely unlikely) case of a page
1779  *   crossing operation.
1780  *
1781  * - Furthermore, we need an efficient 64-bit compile for the
1782  *   64-bit case in order to generate the "number of bytes in
1783  *   the final mask". Again, that could be replaced with a
1784  *   efficient population count instruction or similar.
1785  */
1786 #ifdef CONFIG_DCACHE_WORD_ACCESS
1787 
1788 #include <asm/word-at-a-time.h>
1789 
1790 #ifdef CONFIG_64BIT
1791 
1792 static inline unsigned int fold_hash(unsigned long hash)
1793 {
1794         return hash_64(hash, 32);
1795 }
1796 
1797 #else   /* 32-bit case */
1798 
1799 #define fold_hash(x) (x)
1800 
1801 #endif
1802 
1803 unsigned int full_name_hash(const unsigned char *name, unsigned int len)
1804 {
1805         unsigned long a, mask;
1806         unsigned long hash = 0;
1807 
1808         for (;;) {
1809                 a = load_unaligned_zeropad(name);
1810                 if (len < sizeof(unsigned long))
1811                         break;
1812                 hash += a;
1813                 hash *= 9;
1814                 name += sizeof(unsigned long);
1815                 len -= sizeof(unsigned long);
1816                 if (!len)
1817                         goto done;
1818         }
1819         mask = bytemask_from_count(len);
1820         hash += mask & a;
1821 done:
1822         return fold_hash(hash);
1823 }
1824 EXPORT_SYMBOL(full_name_hash);
1825 
1826 /*
1827  * Calculate the length and hash of the path component, and
1828  * return the "hash_len" as the result.
1829  */
1830 static inline u64 hash_name(const char *name)
1831 {
1832         unsigned long a, b, adata, bdata, mask, hash, len;
1833         const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
1834 
1835         hash = a = 0;
1836         len = -sizeof(unsigned long);
1837         do {
1838                 hash = (hash + a) * 9;
1839                 len += sizeof(unsigned long);
1840                 a = load_unaligned_zeropad(name+len);
1841                 b = a ^ REPEAT_BYTE('/');
1842         } while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants)));
1843 
1844         adata = prep_zero_mask(a, adata, &constants);
1845         bdata = prep_zero_mask(b, bdata, &constants);
1846 
1847         mask = create_zero_mask(adata | bdata);
1848 
1849         hash += a & zero_bytemask(mask);
1850         len += find_zero(mask);
1851         return hashlen_create(fold_hash(hash), len);
1852 }
1853 
1854 #else
1855 
1856 unsigned int full_name_hash(const unsigned char *name, unsigned int len)
1857 {
1858         unsigned long hash = init_name_hash();
1859         while (len--)
1860                 hash = partial_name_hash(*name++, hash);
1861         return end_name_hash(hash);
1862 }
1863 EXPORT_SYMBOL(full_name_hash);
1864 
1865 /*
1866  * We know there's a real path component here of at least
1867  * one character.
1868  */
1869 static inline u64 hash_name(const char *name)
1870 {
1871         unsigned long hash = init_name_hash();
1872         unsigned long len = 0, c;
1873 
1874         c = (unsigned char)*name;
1875         do {
1876                 len++;
1877                 hash = partial_name_hash(c, hash);
1878                 c = (unsigned char)name[len];
1879         } while (c && c != '/');
1880         return hashlen_create(end_name_hash(hash), len);
1881 }
1882 
1883 #endif
1884 
1885 /*
1886  * Name resolution.
1887  * This is the basic name resolution function, turning a pathname into
1888  * the final dentry. We expect 'base' to be positive and a directory.
1889  *
1890  * Returns 0 and nd will have valid dentry and mnt on success.
1891  * Returns error and drops reference to input namei data on failure.
1892  */
1893 static int link_path_walk(const char *name, struct nameidata *nd)
1894 {
1895         int err;
1896 
1897         while (*name=='/')
1898                 name++;
1899         if (!*name)
1900                 return 0;
1901 
1902         /* At this point we know we have a real path component. */
1903         for(;;) {
1904                 u64 hash_len;
1905                 int type;
1906 
1907                 err = may_lookup(nd);
1908                 if (err)
1909                         return err;
1910 
1911                 hash_len = hash_name(name);
1912 
1913                 type = LAST_NORM;
1914                 if (name[0] == '.') switch (hashlen_len(hash_len)) {
1915                         case 2:
1916                                 if (name[1] == '.') {
1917                                         type = LAST_DOTDOT;
1918                                         nd->flags |= LOOKUP_JUMPED;
1919                                 }
1920                                 break;
1921                         case 1:
1922                                 type = LAST_DOT;
1923                 }
1924                 if (likely(type == LAST_NORM)) {
1925                         struct dentry *parent = nd->path.dentry;
1926                         nd->flags &= ~LOOKUP_JUMPED;
1927                         if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
1928                                 struct qstr this = { { .hash_len = hash_len }, .name = name };
1929                                 err = parent->d_op->d_hash(parent, &this);
1930                                 if (err < 0)
1931                                         return err;
1932                                 hash_len = this.hash_len;
1933                                 name = this.name;
1934                         }
1935                 }
1936 
1937                 nd->last.hash_len = hash_len;
1938                 nd->last.name = name;
1939                 nd->last_type = type;
1940 
1941                 name += hashlen_len(hash_len);
1942                 if (!*name)
1943                         goto OK;
1944                 /*
1945                  * If it wasn't NUL, we know it was '/'. Skip that
1946                  * slash, and continue until no more slashes.
1947                  */
1948                 do {
1949                         name++;
1950                 } while (unlikely(*name == '/'));
1951                 if (unlikely(!*name)) {
1952 OK:
1953                         /* pathname body, done */
1954                         if (!nd->depth)
1955                                 return 0;
1956                         name = nd->stack[nd->depth - 1].name;
1957                         /* trailing symlink, done */
1958                         if (!name)
1959                                 return 0;
1960                         /* last component of nested symlink */
1961                         err = walk_component(nd, WALK_GET | WALK_PUT);
1962                 } else {
1963                         err = walk_component(nd, WALK_GET);
1964                 }
1965                 if (err < 0)
1966                         return err;
1967 
1968                 if (err) {
1969                         const char *s = get_link(nd);
1970 
1971                         if (IS_ERR(s))
1972                                 return PTR_ERR(s);
1973                         err = 0;
1974                         if (unlikely(!s)) {
1975                                 /* jumped */
1976                                 put_link(nd);
1977                         } else {
1978                                 nd->stack[nd->depth - 1].name = name;
1979                                 name = s;
1980                                 continue;
1981                         }
1982                 }
1983                 if (unlikely(!d_can_lookup(nd->path.dentry))) {
1984                         if (nd->flags & LOOKUP_RCU) {
1985                                 if (unlazy_walk(nd, NULL, 0))
1986                                         return -ECHILD;
1987                         }
1988                         return -ENOTDIR;
1989                 }
1990         }
1991 }
1992 
1993 static const char *path_init(struct nameidata *nd, unsigned flags)
1994 {
1995         int retval = 0;
1996         const char *s = nd->name->name;
1997 
1998         nd->last_type = LAST_ROOT; /* if there are only slashes... */
1999         nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT;
2000         nd->depth = 0;
2001         if (flags & LOOKUP_ROOT) {
2002                 struct dentry *root = nd->root.dentry;
2003                 struct inode *inode = root->d_inode;
2004                 if (*s) {
2005                         if (!d_can_lookup(root))
2006                                 return ERR_PTR(-ENOTDIR);
2007                         retval = inode_permission(inode, MAY_EXEC);
2008                         if (retval)
2009                                 return ERR_PTR(retval);
2010                 }
2011                 nd->path = nd->root;
2012                 nd->inode = inode;
2013                 if (flags & LOOKUP_RCU) {
2014                         rcu_read_lock();
2015                         nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
2016                         nd->root_seq = nd->seq;
2017                         nd->m_seq = read_seqbegin(&mount_lock);
2018                 } else {
2019                         path_get(&nd->path);
2020                 }
2021                 return s;
2022         }
2023 
2024         nd->root.mnt = NULL;
2025         nd->path.mnt = NULL;
2026         nd->path.dentry = NULL;
2027 
2028         nd->m_seq = read_seqbegin(&mount_lock);
2029         if (*s == '/') {
2030                 if (flags & LOOKUP_RCU)
2031                         rcu_read_lock();
2032                 set_root(nd);
2033                 if (likely(!nd_jump_root(nd)))
2034                         return s;
2035                 nd->root.mnt = NULL;
2036                 rcu_read_unlock();
2037                 return ERR_PTR(-ECHILD);
2038         } else if (nd->dfd == AT_FDCWD) {
2039                 if (flags & LOOKUP_RCU) {
2040                         struct fs_struct *fs = current->fs;
2041                         unsigned seq;
2042 
2043                         rcu_read_lock();
2044 
2045                         do {
2046                                 seq = read_seqcount_begin(&fs->seq);
2047                                 nd->path = fs->pwd;
2048                                 nd->inode = nd->path.dentry->d_inode;
2049                                 nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
2050                         } while (read_seqcount_retry(&fs->seq, seq));
2051                 } else {
2052                         get_fs_pwd(current->fs, &nd->path);
2053                         nd->inode = nd->path.dentry->d_inode;
2054                 }
2055                 return s;
2056         } else {
2057                 /* Caller must check execute permissions on the starting path component */
2058                 struct fd f = fdget_raw(nd->dfd);
2059                 struct dentry *dentry;
2060 
2061                 if (!f.file)
2062                         return ERR_PTR(-EBADF);
2063 
2064                 dentry = f.file->f_path.dentry;
2065 
2066                 if (*s) {
2067                         if (!d_can_lookup(dentry)) {
2068                                 fdput(f);
2069                                 return ERR_PTR(-ENOTDIR);
2070                         }
2071                 }
2072 
2073                 nd->path = f.file->f_path;
2074                 if (flags & LOOKUP_RCU) {
2075                         rcu_read_lock();
2076                         nd->inode = nd->path.dentry->d_inode;
2077                         nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
2078                 } else {
2079                         path_get(&nd->path);
2080                         nd->inode = nd->path.dentry->d_inode;
2081                 }
2082                 fdput(f);
2083                 return s;
2084         }
2085 }
2086 
2087 static const char *trailing_symlink(struct nameidata *nd)
2088 {
2089         const char *s;
2090         int error = may_follow_link(nd);
2091         if (unlikely(error))
2092                 return ERR_PTR(error);
2093         nd->flags |= LOOKUP_PARENT;
2094         nd->stack[0].name = NULL;
2095         s = get_link(nd);
2096         return s ? s : "";
2097 }
2098 
2099 static inline int lookup_last(struct nameidata *nd)
2100 {
2101         if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len])
2102                 nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
2103 
2104         nd->flags &= ~LOOKUP_PARENT;
2105         return walk_component(nd,
2106                         nd->flags & LOOKUP_FOLLOW
2107                                 ? nd->depth
2108                                         ? WALK_PUT | WALK_GET
2109                                         : WALK_GET
2110                                 : 0);
2111 }
2112 
2113 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
2114 static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path)
2115 {
2116         const char *s = path_init(nd, flags);
2117         int err;
2118 
2119         if (IS_ERR(s))
2120                 return PTR_ERR(s);
2121         while (!(err = link_path_walk(s, nd))
2122                 && ((err = lookup_last(nd)) > 0)) {
2123                 s = trailing_symlink(nd);
2124                 if (IS_ERR(s)) {
2125                         err = PTR_ERR(s);
2126                         break;
2127                 }
2128         }
2129         if (!err)
2130                 err = complete_walk(nd);
2131 
2132         if (!err && nd->flags & LOOKUP_DIRECTORY)
2133                 if (!d_can_lookup(nd->path.dentry))
2134                         err = -ENOTDIR;
2135         if (!err) {
2136                 *path = nd->path;
2137                 nd->path.mnt = NULL;
2138                 nd->path.dentry = NULL;
2139         }
2140         terminate_walk(nd);
2141         return err;
2142 }
2143 
2144 static int filename_lookup(int dfd, struct filename *name, unsigned flags,
2145                            struct path *path, struct path *root)
2146 {
2147         int retval;
2148         struct nameidata nd;
2149         if (IS_ERR(name))
2150                 return PTR_ERR(name);
2151         if (unlikely(root)) {
2152                 nd.root = *root;
2153                 flags |= LOOKUP_ROOT;
2154         }
2155         set_nameidata(&nd, dfd, name);
2156         retval = path_lookupat(&nd, flags | LOOKUP_RCU, path);
2157         if (unlikely(retval == -ECHILD))
2158                 retval = path_lookupat(&nd, flags, path);
2159         if (unlikely(retval == -ESTALE))
2160                 retval = path_lookupat(&nd, flags | LOOKUP_REVAL, path);
2161 
2162         if (likely(!retval))
2163                 audit_inode(name, path->dentry, flags & LOOKUP_PARENT);
2164         restore_nameidata();
2165         putname(name);
2166         return retval;
2167 }
2168 
2169 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
2170 static int path_parentat(struct nameidata *nd, unsigned flags,
2171                                 struct path *parent)
2172 {
2173         const char *s = path_init(nd, flags);
2174         int err;
2175         if (IS_ERR(s))
2176                 return PTR_ERR(s);
2177         err = link_path_walk(s, nd);
2178         if (!err)
2179                 err = complete_walk(nd);
2180         if (!err) {
2181                 *parent = nd->path;
2182                 nd->path.mnt = NULL;
2183                 nd->path.dentry = NULL;
2184         }
2185         terminate_walk(nd);
2186         return err;
2187 }
2188 
2189 static struct filename *filename_parentat(int dfd, struct filename *name,
2190                                 unsigned int flags, struct path *parent,
2191                                 struct qstr *last, int *type)
2192 {
2193         int retval;
2194         struct nameidata nd;
2195 
2196         if (IS_ERR(name))
2197                 return name;
2198         set_nameidata(&nd, dfd, name);
2199         retval = path_parentat(&nd, flags | LOOKUP_RCU, parent);
2200         if (unlikely(retval == -ECHILD))
2201                 retval = path_parentat(&nd, flags, parent);
2202         if (unlikely(retval == -ESTALE))
2203                 retval = path_parentat(&nd, flags | LOOKUP_REVAL, parent);
2204         if (likely(!retval)) {
2205                 *last = nd.last;
2206                 *type = nd.last_type;
2207                 audit_inode(name, parent->dentry, LOOKUP_PARENT);
2208         } else {
2209                 putname(name);
2210                 name = ERR_PTR(retval);
2211         }
2212         restore_nameidata();
2213         return name;
2214 }
2215 
2216 /* does lookup, returns the object with parent locked */
2217 struct dentry *kern_path_locked(const char *name, struct path *path)
2218 {
2219         struct filename *filename;
2220         struct dentry *d;
2221         struct qstr last;
2222         int type;
2223 
2224         filename = filename_parentat(AT_FDCWD, getname_kernel(name), 0, path,
2225                                     &last, &type);
2226         if (IS_ERR(filename))
2227                 return ERR_CAST(filename);
2228         if (unlikely(type != LAST_NORM)) {
2229                 path_put(path);
2230                 putname(filename);
2231                 return ERR_PTR(-EINVAL);
2232         }
2233         inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
2234         d = __lookup_hash(&last, path->dentry, 0);
2235         if (IS_ERR(d)) {
2236                 inode_unlock(path->dentry->d_inode);
2237                 path_put(path);
2238         }
2239         putname(filename);
2240         return d;
2241 }
2242 
2243 int kern_path(const char *name, unsigned int flags, struct path *path)
2244 {
2245         return filename_lookup(AT_FDCWD, getname_kernel(name),
2246                                flags, path, NULL);
2247 }
2248 EXPORT_SYMBOL(kern_path);
2249 
2250 /**
2251  * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
2252  * @dentry:  pointer to dentry of the base directory
2253  * @mnt: pointer to vfs mount of the base directory
2254  * @name: pointer to file name
2255  * @flags: lookup flags
2256  * @path: pointer to struct path to fill
2257  */
2258 int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
2259                     const char *name, unsigned int flags,
2260                     struct path *path)
2261 {
2262         struct path root = {.mnt = mnt, .dentry = dentry};
2263         /* the first argument of filename_lookup() is ignored with root */
2264         return filename_lookup(AT_FDCWD, getname_kernel(name),
2265                                flags , path, &root);
2266 }
2267 EXPORT_SYMBOL(vfs_path_lookup);
2268 
2269 /**
2270  * lookup_hash - lookup single pathname component on already hashed name
2271  * @name:       name and hash to lookup
2272  * @base:       base directory to lookup from
2273  *
2274  * The name must have been verified and hashed (see lookup_one_len()).  Using
2275  * this after just full_name_hash() is unsafe.
2276  *
2277  * This function also doesn't check for search permission on base directory.
2278  *
2279  * Use lookup_one_len_unlocked() instead, unless you really know what you are
2280  * doing.
2281  *
2282  * Do not hold i_mutex; this helper takes i_mutex if necessary.
2283  */
2284 struct dentry *lookup_hash(const struct qstr *name, struct dentry *base)
2285 {
2286         struct dentry *ret;
2287 
2288         ret = lookup_dcache(name, base, 0);
2289         if (!ret)
2290                 ret = lookup_slow(name, base, 0);
2291 
2292         return ret;
2293 }
2294 EXPORT_SYMBOL(lookup_hash);
2295 
2296 /**
2297  * lookup_one_len - filesystem helper to lookup single pathname component
2298  * @name:       pathname component to lookup
2299  * @base:       base directory to lookup from
2300  * @len:        maximum length @len should be interpreted to
2301  *
2302  * Note that this routine is purely a helper for filesystem usage and should
2303  * not be called by generic code.
2304  *
2305  * The caller must hold base->i_mutex.
2306  */
2307 struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
2308 {
2309         struct qstr this;
2310         unsigned int c;
2311         int err;
2312 
2313         WARN_ON_ONCE(!inode_is_locked(base->d_inode));
2314 
2315         this.name = name;
2316         this.len = len;
2317         this.hash = full_name_hash(name, len);
2318         if (!len)
2319                 return ERR_PTR(-EACCES);
2320 
2321         if (unlikely(name[0] == '.')) {
2322                 if (len < 2 || (len == 2 && name[1] == '.'))
2323                         return ERR_PTR(-EACCES);
2324         }
2325 
2326         while (len--) {
2327                 c = *(const unsigned char *)name++;
2328                 if (c == '/' || c == '\0')
2329                         return ERR_PTR(-EACCES);
2330         }
2331         /*
2332          * See if the low-level filesystem might want
2333          * to use its own hash..
2334          */
2335         if (base->d_flags & DCACHE_OP_HASH) {
2336                 int err = base->d_op->d_hash(base, &this);
2337                 if (err < 0)
2338                         return ERR_PTR(err);
2339         }
2340 
2341         err = inode_permission(base->d_inode, MAY_EXEC);
2342         if (err)
2343                 return ERR_PTR(err);
2344 
2345         return __lookup_hash(&this, base, 0);
2346 }
2347 EXPORT_SYMBOL(lookup_one_len);
2348 
2349 /**
2350  * lookup_one_len_unlocked - filesystem helper to lookup single pathname component
2351  * @name:       pathname component to lookup
2352  * @base:       base directory to lookup from
2353  * @len:        maximum length @len should be interpreted to
2354  *
2355  * Note that this routine is purely a helper for filesystem usage and should
2356  * not be called by generic code.
2357  *
2358  * Unlike lookup_one_len, it should be called without the parent
2359  * i_mutex held, and will take the i_mutex itself if necessary.
2360  */
2361 struct dentry *lookup_one_len_unlocked(const char *name,
2362                                        struct dentry *base, int len)
2363 {
2364         struct qstr this;
2365         unsigned int c;
2366         int err;
2367 
2368         this.name = name;
2369         this.len = len;
2370         this.hash = full_name_hash(name, len);
2371         if (!len)
2372                 return ERR_PTR(-EACCES);
2373 
2374         if (unlikely(name[0] == '.')) {
2375                 if (len < 2 || (len == 2 && name[1] == '.'))
2376                         return ERR_PTR(-EACCES);
2377         }
2378 
2379         while (len--) {
2380                 c = *(const unsigned char *)name++;
2381                 if (c == '/' || c == '\0')
2382                         return ERR_PTR(-EACCES);
2383         }
2384         /*
2385          * See if the low-level filesystem might want
2386          * to use its own hash..
2387          */
2388         if (base->d_flags & DCACHE_OP_HASH) {
2389                 int err = base->d_op->d_hash(base, &this);
2390                 if (err < 0)
2391                         return ERR_PTR(err);
2392         }
2393 
2394         err = inode_permission(base->d_inode, MAY_EXEC);
2395         if (err)
2396                 return ERR_PTR(err);
2397 
2398         return lookup_hash(&this, base);
2399 }
2400 EXPORT_SYMBOL(lookup_one_len_unlocked);
2401 
2402 int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
2403                  struct path *path, int *empty)
2404 {
2405         return filename_lookup(dfd, getname_flags(name, flags, empty),
2406                                flags, path, NULL);
2407 }
2408 EXPORT_SYMBOL(user_path_at_empty);
2409 
2410 /*
2411  * NB: most callers don't do anything directly with the reference to the
2412  *     to struct filename, but the nd->last pointer points into the name string
2413  *     allocated by getname. So we must hold the reference to it until all
2414  *     path-walking is complete.
2415  */
2416 static inline struct filename *
2417 user_path_parent(int dfd, const char __user *path,
2418                  struct path *parent,
2419                  struct qstr *last,
2420                  int *type,
2421                  unsigned int flags)
2422 {
2423         /* only LOOKUP_REVAL is allowed in extra flags */
2424         return filename_parentat(dfd, getname(path), flags & LOOKUP_REVAL,
2425                                  parent, last, type);
2426 }
2427 
2428 /**
2429  * mountpoint_last - look up last component for umount
2430  * @nd:   pathwalk nameidata - currently pointing at parent directory of "last"
2431  * @path: pointer to container for result
2432  *
2433  * This is a special lookup_last function just for umount. In this case, we
2434  * need to resolve the path without doing any revalidation.
2435  *
2436  * The nameidata should be the result of doing a LOOKUP_PARENT pathwalk. Since
2437  * mountpoints are always pinned in the dcache, their ancestors are too. Thus,
2438  * in almost all cases, this lookup will be served out of the dcache. The only
2439  * cases where it won't are if nd->last refers to a symlink or the path is
2440  * bogus and it doesn't exist.
2441  *
2442  * Returns:
2443  * -error: if there was an error during lookup. This includes -ENOENT if the
2444  *         lookup found a negative dentry. The nd->path reference will also be
2445  *         put in this case.
2446  *
2447  * 0:      if we successfully resolved nd->path and found it to not to be a
2448  *         symlink that needs to be followed. "path" will also be populated.
2449  *         The nd->path reference will also be put.
2450  *
2451  * 1:      if we successfully resolved nd->last and found it to be a symlink
2452  *         that needs to be followed. "path" will be populated with the path
2453  *         to the link, and nd->path will *not* be put.
2454  */
2455 static int
2456 mountpoint_last(struct nameidata *nd, struct path *path)
2457 {
2458         int error = 0;
2459         struct dentry *dentry;
2460         struct dentry *dir = nd->path.dentry;
2461 
2462         /* If we're in rcuwalk, drop out of it to handle last component */
2463         if (nd->flags & LOOKUP_RCU) {
2464                 if (unlazy_walk(nd, NULL, 0))
2465                         return -ECHILD;
2466         }
2467 
2468         nd->flags &= ~LOOKUP_PARENT;
2469 
2470         if (unlikely(nd->last_type != LAST_NORM)) {
2471                 error = handle_dots(nd, nd->last_type);
2472                 if (error)
2473                         return error;
2474                 dentry = dget(nd->path.dentry);
2475         } else {
2476                 dentry = d_lookup(dir, &nd->last);
2477                 if (!dentry) {
2478                         /*
2479                          * No cached dentry. Mounted dentries are pinned in the
2480                          * cache, so that means that this dentry is probably
2481                          * a symlink or the path doesn't actually point
2482                          * to a mounted dentry.
2483                          */
2484                         dentry = lookup_slow(&nd->last, dir,
2485                                              nd->flags | LOOKUP_NO_REVAL);
2486                         if (IS_ERR(dentry))
2487                                 return PTR_ERR(dentry);
2488                 }
2489         }
2490         if (d_is_negative(dentry)) {
2491                 dput(dentry);
2492                 return -ENOENT;
2493         }
2494         if (nd->depth)
2495                 put_link(nd);
2496         path->dentry = dentry;
2497         path->mnt = nd->path.mnt;
2498         error = should_follow_link(nd, path, nd->flags & LOOKUP_FOLLOW,
2499                                    d_backing_inode(dentry), 0);
2500         if (unlikely(error))
2501                 return error;
2502         mntget(path->mnt);
2503         follow_mount(path);
2504         return 0;
2505 }
2506 
2507 /**
2508  * path_mountpoint - look up a path to be umounted
2509  * @nd:         lookup context
2510  * @flags:      lookup flags
2511  * @path:       pointer to container for result
2512  *
2513  * Look up the given name, but don't attempt to revalidate the last component.
2514  * Returns 0 and "path" will be valid on success; Returns error otherwise.
2515  */
2516 static int
2517 path_mountpoint(struct nameidata *nd, unsigned flags, struct path *path)
2518 {
2519         const char *s = path_init(nd, flags);
2520         int err;
2521         if (IS_ERR(s))
2522                 return PTR_ERR(s);
2523         while (!(err = link_path_walk(s, nd)) &&
2524                 (err = mountpoint_last(nd, path)) > 0) {
2525                 s = trailing_symlink(nd);
2526                 if (IS_ERR(s)) {
2527                         err = PTR_ERR(s);
2528                         break;
2529                 }
2530         }
2531         terminate_walk(nd);
2532         return err;
2533 }
2534 
2535 static int
2536 filename_mountpoint(int dfd, struct filename *name, struct path *path,
2537                         unsigned int flags)
2538 {
2539         struct nameidata nd;
2540         int error;
2541         if (IS_ERR(name))
2542                 return PTR_ERR(name);
2543         set_nameidata(&nd, dfd, name);
2544         error = path_mountpoint(&nd, flags | LOOKUP_RCU, path);
2545         if (unlikely(error == -ECHILD))
2546                 error = path_mountpoint(&nd, flags, path);
2547         if (unlikely(error == -ESTALE))
2548                 error = path_mountpoint(&nd, flags | LOOKUP_REVAL, path);
2549         if (likely(!error))
2550                 audit_inode(name, path->dentry, 0);
2551         restore_nameidata();
2552         putname(name);
2553         return error;
2554 }
2555 
2556 /**
2557  * user_path_mountpoint_at - lookup a path from userland in order to umount it
2558  * @dfd:        directory file descriptor
2559  * @name:       pathname from userland
2560  * @flags:      lookup flags
2561  * @path:       pointer to container to hold result
2562  *
2563  * A umount is a special case for path walking. We're not actually interested
2564  * in the inode in this situation, and ESTALE errors can be a problem. We
2565  * simply want track down the dentry and vfsmount attached at the mountpoint
2566  * and avoid revalidating the last component.
2567  *
2568  * Returns 0 and populates "path" on success.
2569  */
2570 int
2571 user_path_mountpoint_at(int dfd, const char __user *name, unsigned int flags,
2572                         struct path *path)
2573 {
2574         return filename_mountpoint(dfd, getname(name), path, flags);
2575 }
2576 
2577 int
2578 kern_path_mountpoint(int dfd, const char *name, struct path *path,
2579                         unsigned int flags)
2580 {
2581         return filename_mountpoint(dfd, getname_kernel(name), path, flags);
2582 }
2583 EXPORT_SYMBOL(kern_path_mountpoint);
2584 
2585 int __check_sticky(struct inode *dir, struct inode *inode)
2586 {
2587         kuid_t fsuid = current_fsuid();
2588 
2589         if (uid_eq(inode->i_uid, fsuid))
2590                 return 0;
2591         if (uid_eq(dir->i_uid, fsuid))
2592                 return 0;
2593         return !capable_wrt_inode_uidgid(inode, CAP_FOWNER);
2594 }
2595 EXPORT_SYMBOL(__check_sticky);
2596 
2597 /*
2598  *      Check whether we can remove a link victim from directory dir, check
2599  *  whether the type of victim is right.
2600  *  1. We can't do it if dir is read-only (done in permission())
2601  *  2. We should have write and exec permissions on dir
2602  *  3. We can't remove anything from append-only dir
2603  *  4. We can't do anything with immutable dir (done in permission())
2604  *  5. If the sticky bit on dir is set we should either
2605  *      a. be owner of dir, or
2606  *      b. be owner of victim, or
2607  *      c. have CAP_FOWNER capability
2608  *  6. If the victim is append-only or immutable we can't do antyhing with
2609  *     links pointing to it.
2610  *  7. If we were asked to remove a directory and victim isn't one - ENOTDIR.
2611  *  8. If we were asked to remove a non-directory and victim isn't one - EISDIR.
2612  *  9. We can't remove a root or mountpoint.
2613  * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
2614  *     nfs_async_unlink().
2615  */
2616 static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
2617 {
2618         struct inode *inode = d_backing_inode(victim);
2619         int error;
2620 
2621         if (d_is_negative(victim))
2622                 return -ENOENT;
2623         BUG_ON(!inode);
2624 
2625         BUG_ON(victim->d_parent->d_inode != dir);
2626         audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
2627 
2628         error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
2629         if (error)
2630                 return error;
2631         if (IS_APPEND(dir))
2632                 return -EPERM;
2633 
2634         if (check_sticky(dir, inode) || IS_APPEND(inode) ||
2635             IS_IMMUTABLE(inode) || IS_SWAPFILE(inode))
2636                 return -EPERM;
2637         if (isdir) {
2638                 if (!d_is_dir(victim))
2639                         return -ENOTDIR;
2640                 if (IS_ROOT(victim))
2641                         return -EBUSY;
2642         } else if (d_is_dir(victim))
2643                 return -EISDIR;
2644         if (IS_DEADDIR(dir))
2645                 return -ENOENT;
2646         if (victim->d_flags & DCACHE_NFSFS_RENAMED)
2647                 return -EBUSY;
2648         return 0;
2649 }
2650 
2651 /*      Check whether we can create an object with dentry child in directory
2652  *  dir.
2653  *  1. We can't do it if child already exists (open has special treatment for
2654  *     this case, but since we are inlined it's OK)
2655  *  2. We can't do it if dir is read-only (done in permission())
2656  *  3. We should have write and exec permissions on dir
2657  *  4. We can't do it if dir is immutable (done in permission())
2658  */
2659 static inline int may_create(struct inode *dir, struct dentry *child)
2660 {
2661         audit_inode_child(dir, child, AUDIT_TYPE_CHILD_CREATE);
2662         if (child->d_inode)
2663                 return -EEXIST;
2664         if (IS_DEADDIR(dir))
2665                 return -ENOENT;
2666         return inode_permission(dir, MAY_WRITE | MAY_EXEC);
2667 }
2668 
2669 /*
2670  * p1 and p2 should be directories on the same fs.
2671  */
2672 struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
2673 {
2674         struct dentry *p;
2675 
2676         if (p1 == p2) {
2677                 inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2678                 return NULL;
2679         }
2680 
2681         mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
2682 
2683         p = d_ancestor(p2, p1);
2684         if (p) {
2685                 inode_lock_nested(p2->d_inode, I_MUTEX_PARENT);
2686                 inode_lock_nested(p1->d_inode, I_MUTEX_CHILD);
2687                 return p;
2688         }
2689 
2690         p = d_ancestor(p1, p2);
2691         if (p) {
2692                 inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2693                 inode_lock_nested(p2->d_inode, I_MUTEX_CHILD);
2694                 return p;
2695         }
2696 
2697         inode_lock_nested(p1->d_inode, I_MUTEX_PARENT);
2698         inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2);
2699         return NULL;
2700 }
2701 EXPORT_SYMBOL(lock_rename);
2702 
2703 void unlock_rename(struct dentry *p1, struct dentry *p2)
2704 {
2705         inode_unlock(p1->d_inode);
2706         if (p1 != p2) {
2707                 inode_unlock(p2->d_inode);
2708                 mutex_unlock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
2709         }
2710 }
2711 EXPORT_SYMBOL(unlock_rename);
2712 
2713 int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
2714                 bool want_excl)
2715 {
2716         int error = may_create(dir, dentry);
2717         if (error)
2718                 return error;
2719 
2720         if (!dir->i_op->create)
2721                 return -EACCES; /* shouldn't it be ENOSYS? */
2722         mode &= S_IALLUGO;
2723         mode |= S_IFREG;
2724         error = security_inode_create(dir, dentry, mode);
2725         if (error)
2726                 return error;
2727         error = dir->i_op->create(dir, dentry, mode, want_excl);
2728         if (!error)
2729                 fsnotify_create(dir, dentry);
2730         return error;
2731 }
2732 EXPORT_SYMBOL(vfs_create);
2733 
2734 static int may_open(struct path *path, int acc_mode, int flag)
2735 {
2736         struct dentry *dentry = path->dentry;
2737         struct inode *inode = dentry->d_inode;
2738         int error;
2739 
2740         if (!inode)
2741                 return -ENOENT;
2742 
2743         switch (inode->i_mode & S_IFMT) {
2744         case S_IFLNK:
2745                 return -ELOOP;
2746         case S_IFDIR:
2747                 if (acc_mode & MAY_WRITE)
2748                         return -EISDIR;
2749                 break;
2750         case S_IFBLK:
2751         case S_IFCHR:
2752                 if (path->mnt->mnt_flags & MNT_NODEV)
2753                         return -EACCES;
2754                 /*FALLTHRU*/
2755         case S_IFIFO:
2756         case S_IFSOCK:
2757                 flag &= ~O_TRUNC;
2758                 break;
2759         }
2760 
2761         error = inode_permission(inode, MAY_OPEN | acc_mode);
2762         if (error)
2763                 return error;
2764 
2765         /*
2766          * An append-only file must be opened in append mode for writing.
2767          */
2768         if (IS_APPEND(inode)) {
2769                 if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
2770                         return -EPERM;
2771                 if (flag & O_TRUNC)
2772                         return -EPERM;
2773         }
2774 
2775         /* O_NOATIME can only be set by the owner or superuser */
2776         if (flag & O_NOATIME && !inode_owner_or_capable(inode))
2777                 return -EPERM;
2778 
2779         return 0;
2780 }
2781 
2782 static int handle_truncate(struct file *filp)
2783 {
2784         struct path *path = &filp->f_path;
2785         struct inode *inode = path->dentry->d_inode;
2786         int error = get_write_access(inode);
2787         if (error)
2788                 return error;
2789         /*
2790          * Refuse to truncate files with mandatory locks held on them.
2791          */
2792         error = locks_verify_locked(filp);
2793         if (!error)
2794                 error = security_path_truncate(path);
2795         if (!error) {
2796                 error = do_truncate(path->dentry, 0,
2797                                     ATTR_MTIME|ATTR_CTIME|ATTR_OPEN,
2798                                     filp);
2799         }
2800         put_write_access(inode);
2801         return error;
2802 }
2803 
2804 static inline int open_to_namei_flags(int flag)
2805 {
2806         if ((flag & O_ACCMODE) == 3)
2807                 flag--;
2808         return flag;
2809 }
2810 
2811 static int may_o_create(struct path *dir, struct dentry *dentry, umode_t mode)
2812 {
2813         int error = security_path_mknod(dir, dentry, mode, 0);
2814         if (error)
2815                 return error;
2816 
2817         error = inode_permission(dir->dentry->d_inode, MAY_WRITE | MAY_EXEC);
2818         if (error)
2819                 return error;
2820 
2821         return security_inode_create(dir->dentry->d_inode, dentry, mode);
2822 }
2823 
2824 /*
2825  * Attempt to atomically look up, create and open a file from a negative
2826  * dentry.
2827  *
2828  * Returns 0 if successful.  The file will have been created and attached to
2829  * @file by the filesystem calling finish_open().
2830  *
2831  * Returns 1 if the file was looked up only or didn't need creating.  The
2832  * caller will need to perform the open themselves.  @path will have been
2833  * updated to point to the new dentry.  This may be negative.
2834  *
2835  * Returns an error code otherwise.
2836  */
2837 static int atomic_open(struct nameidata *nd, struct dentry *dentry,
2838                         struct path *path, struct file *file,
2839                         const struct open_flags *op,
2840                         bool got_write, bool need_lookup,
2841                         int *opened)
2842 {
2843         struct inode *dir =  nd->path.dentry->d_inode;
2844         unsigned open_flag = open_to_namei_flags(op->open_flag);
2845         umode_t mode;
2846         int error;
2847         int acc_mode;
2848         int create_error = 0;
2849         struct dentry *const DENTRY_NOT_SET = (void *) -1UL;
2850         bool excl;
2851 
2852         BUG_ON(dentry->d_inode);
2853 
2854         /* Don't create child dentry for a dead directory. */
2855         if (unlikely(IS_DEADDIR(dir))) {
2856                 error = -ENOENT;
2857                 goto out;
2858         }
2859 
2860         mode = op->mode;
2861         if ((open_flag & O_CREAT) && !IS_POSIXACL(dir))
2862                 mode &= ~current_umask();
2863 
2864         excl = (open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT);
2865         if (excl)
2866                 open_flag &= ~O_TRUNC;
2867 
2868         /*
2869          * Checking write permission is tricky, bacuse we don't know if we are
2870          * going to actually need it: O_CREAT opens should work as long as the
2871          * file exists.  But checking existence breaks atomicity.  The trick is
2872          * to check access and if not granted clear O_CREAT from the flags.
2873          *
2874          * Another problem is returing the "right" error value (e.g. for an
2875          * O_EXCL open we want to return EEXIST not EROFS).
2876          */
2877         if (((open_flag & (O_CREAT | O_TRUNC)) ||
2878             (open_flag & O_ACCMODE) != O_RDONLY) && unlikely(!got_write)) {
2879                 if (!(open_flag & O_CREAT)) {
2880                         /*
2881                          * No O_CREATE -> atomicity not a requirement -> fall
2882                          * back to lookup + open
2883                          */
2884                         goto no_open;
2885                 } else if (open_flag & (O_EXCL | O_TRUNC)) {
2886                         /* Fall back and fail with the right error */
2887                         create_error = -EROFS;
2888                         goto no_open;
2889                 } else {
2890                         /* No side effects, safe to clear O_CREAT */
2891                         create_error = -EROFS;
2892                         open_flag &= ~O_CREAT;
2893                 }
2894         }
2895 
2896         if (open_flag & O_CREAT) {
2897                 error = may_o_create(&nd->path, dentry, mode);
2898                 if (error) {
2899                         create_error = error;
2900                         if (open_flag & O_EXCL)
2901                                 goto no_open;
2902                         open_flag &= ~O_CREAT;
2903                 }
2904         }
2905 
2906         if (nd->flags & LOOKUP_DIRECTORY)
2907                 open_flag |= O_DIRECTORY;
2908 
2909         file->f_path.dentry = DENTRY_NOT_SET;
2910         file->f_path.mnt = nd->path.mnt;
2911         error = dir->i_op->atomic_open(dir, dentry, file, open_flag, mode,
2912                                       opened);
2913         if (error < 0) {
2914                 if (create_error && error == -ENOENT)
2915                         error = create_error;
2916                 goto out;
2917         }
2918 
2919         if (error) {    /* returned 1, that is */
2920                 if (WARN_ON(file->f_path.dentry == DENTRY_NOT_SET)) {
2921                         error = -EIO;
2922                         goto out;
2923                 }
2924                 if (file->f_path.dentry) {
2925                         dput(dentry);
2926                         dentry = file->f_path.dentry;
2927                 }
2928                 if (*opened & FILE_CREATED)
2929                         fsnotify_create(dir, dentry);
2930                 if (!dentry->d_inode) {
2931                         WARN_ON(*opened & FILE_CREATED);
2932                         if (create_error) {
2933                                 error = create_error;
2934                                 goto out;
2935                         }
2936                 } else {
2937                         if (excl && !(*opened & FILE_CREATED)) {
2938                                 error = -EEXIST;
2939                                 goto out;
2940                         }
2941                 }
2942                 goto looked_up;
2943         }
2944 
2945         /*
2946          * We didn't have the inode before the open, so check open permission
2947          * here.
2948          */
2949         acc_mode = op->acc_mode;
2950         if (*opened & FILE_CREATED) {
2951                 WARN_ON(!(open_flag & O_CREAT));
2952                 fsnotify_create(dir, dentry);
2953                 acc_mode = 0;
2954         }
2955         error = may_open(&file->f_path, acc_mode, open_flag);
2956         if (error)
2957                 fput(file);
2958 
2959 out:
2960         dput(dentry);
2961         return error;
2962 
2963 no_open:
2964         if (need_lookup) {
2965                 dentry = lookup_real(dir, dentry, nd->flags);
2966                 if (IS_ERR(dentry))
2967                         return PTR_ERR(dentry);
2968         }
2969         if (create_error && !dentry->d_inode) {
2970                 error = create_error;
2971                 goto out;
2972         }
2973 looked_up:
2974         path->dentry = dentry;
2975         path->mnt = nd->path.mnt;
2976         return 1;
2977 }
2978 
2979 /*
2980  * Look up and maybe create and open the last component.
2981  *
2982  * Must be called with i_mutex held on parent.
2983  *
2984  * Returns 0 if the file was successfully atomically created (if necessary) and
2985  * opened.  In this case the file will be returned attached to @file.
2986  *
2987  * Returns 1 if the file was not completely opened at this time, though lookups
2988  * and creations will have been performed and the dentry returned in @path will
2989  * be positive upon return if O_CREAT was specified.  If O_CREAT wasn't
2990  * specified then a negative dentry may be returned.
2991  *
2992  * An error code is returned otherwise.
2993  *
2994  * FILE_CREATE will be set in @*opened if the dentry was created and will be
2995  * cleared otherwise prior to returning.
2996  */
2997 static int lookup_open(struct nameidata *nd, struct path *path,
2998                         struct file *file,
2999                         const struct open_flags *op,
3000                         bool got_write, int *opened)
3001 {
3002         struct dentry *dir = nd->path.dentry;
3003         struct inode *dir_inode = dir->d_inode;
3004         struct dentry *dentry;
3005         int error;
3006         bool need_lookup = false;
3007 
3008         *opened &= ~FILE_CREATED;
3009         dentry = lookup_dcache(&nd->last, dir, nd->flags);
3010         if (IS_ERR(dentry))
3011                 return PTR_ERR(dentry);
3012 
3013         if (!dentry) {
3014                 dentry = d_alloc(dir, &nd->last);
3015                 if (unlikely(!dentry))
3016                         return -ENOMEM;
3017                 need_lookup = true;
3018         } else if (dentry->d_inode) {
3019                 /* Cached positive dentry: will open in f_op->open */
3020                 goto out_no_open;
3021         }
3022 
3023         if ((nd->flags & LOOKUP_OPEN) && dir_inode->i_op->atomic_open) {
3024                 return atomic_open(nd, dentry, path, file, op, got_write,
3025                                    need_lookup, opened);
3026         }
3027 
3028         if (need_lookup) {
3029                 BUG_ON(dentry->d_inode);
3030 
3031                 dentry = lookup_real(dir_inode, dentry, nd->flags);
3032                 if (IS_ERR(dentry))
3033                         return PTR_ERR(dentry);
3034         }
3035 
3036         /* Negative dentry, just create the file */
3037         if (!dentry->d_inode && (op->open_flag & O_CREAT)) {
3038                 umode_t mode = op->mode;
3039                 if (!IS_POSIXACL(dir->d_inode))
3040                         mode &= ~current_umask();
3041                 /*
3042                  * This write is needed to ensure that a
3043                  * rw->ro transition does not occur between
3044                  * the time when the file is created and when
3045                  * a permanent write count is taken through
3046                  * the 'struct file' in finish_open().
3047                  */
3048                 if (!got_write) {
3049                         error = -EROFS;
3050                         goto out_dput;
3051                 }
3052                 *opened |= FILE_CREATED;
3053                 error = security_path_mknod(&nd->path, dentry, mode, 0);
3054                 if (error)
3055                         goto out_dput;
3056                 error = vfs_create(dir->d_inode, dentry, mode,
3057                                    nd->flags & LOOKUP_EXCL);
3058                 if (error)
3059                         goto out_dput;
3060         }
3061 out_no_open:
3062         path->dentry = dentry;
3063         path->mnt = nd->path.mnt;
3064         return 1;
3065 
3066 out_dput:
3067         dput(dentry);
3068         return error;
3069 }
3070 
3071 /*
3072  * Handle the last step of open()
3073  */
3074 static int do_last(struct nameidata *nd,
3075                    struct file *file, const struct open_flags *op,
3076                    int *opened)
3077 {
3078         struct dentry *dir = nd->path.dentry;
3079         int open_flag = op->open_flag;
3080         bool will_truncate = (open_flag & O_TRUNC) != 0;
3081         bool got_write = false;
3082         int acc_mode = op->acc_mode;
3083         unsigned seq;
3084         struct inode *inode;
3085         struct path save_parent = { .dentry = NULL, .mnt = NULL };
3086         struct path path;
3087         bool retried = false;
3088         int error;
3089 
3090         nd->flags &= ~LOOKUP_PARENT;
3091         nd->flags |= op->intent;
3092 
3093         if (nd->last_type != LAST_NORM) {
3094                 error = handle_dots(nd, nd->last_type);
3095                 if (unlikely(error))
3096                         return error;
3097                 goto finish_open;
3098         }
3099 
3100         if (!(open_flag & O_CREAT)) {
3101                 if (nd->last.name[nd->last.len])
3102                         nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
3103                 /* we _can_ be in RCU mode here */
3104                 error = lookup_fast(nd, &path, &inode, &seq);
3105                 if (likely(error > 0))
3106                         goto finish_lookup;
3107 
3108                 if (error < 0)
3109                         return error;
3110 
3111                 BUG_ON(nd->inode != dir->d_inode);
3112                 BUG_ON(nd->flags & LOOKUP_RCU);
3113         } else {
3114                 /* create side of things */
3115                 /*
3116                  * This will *only* deal with leaving RCU mode - LOOKUP_JUMPED
3117                  * has been cleared when we got to the last component we are
3118                  * about to look up
3119                  */
3120                 error = complete_walk(nd);
3121                 if (error)
3122                         return error;
3123 
3124                 audit_inode(nd->name, dir, LOOKUP_PARENT);
3125                 /* trailing slashes? */
3126                 if (unlikely(nd->last.name[nd->last.len]))
3127                         return -EISDIR;
3128         }
3129 
3130 retry_lookup:
3131         if (op->open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {
3132                 error = mnt_want_write(nd->path.mnt);
3133                 if (!error)
3134                         got_write = true;
3135                 /*
3136                  * do _not_ fail yet - we might not need that or fail with
3137                  * a different error; let lookup_open() decide; we'll be
3138                  * dropping this one anyway.
3139                  */
3140         }
3141         inode_lock(dir->d_inode);
3142         error = lookup_open(nd, &path, file, op, got_write, opened);
3143         inode_unlock(dir->d_inode);
3144 
3145         if (error <= 0) {
3146                 if (error)
3147                         goto out;
3148 
3149                 if ((*opened & FILE_CREATED) ||
3150                     !S_ISREG(file_inode(file)->i_mode))
3151                         will_truncate = false;
3152 
3153                 audit_inode(nd->name, file->f_path.dentry, 0);
3154                 goto opened;
3155         }
3156 
3157         if (*opened & FILE_CREATED) {
3158                 /* Don't check for write permission, don't truncate */
3159                 open_flag &= ~O_TRUNC;
3160                 will_truncate = false;
3161                 acc_mode = 0;
3162                 path_to_nameidata(&path, nd);
3163                 goto finish_open_created;
3164         }
3165 
3166         /*
3167          * If atomic_open() acquired write access it is dropped now due to
3168          * possible mount and symlink following (this might be optimized away if
3169          * necessary...)
3170          */
3171         if (got_write) {
3172                 mnt_drop_write(nd->path.mnt);
3173                 got_write = false;
3174         }
3175 
3176         if (unlikely(d_is_negative(path.dentry))) {
3177                 path_to_nameidata(&path, nd);
3178                 return -ENOENT;
3179         }
3180 
3181         /*
3182          * create/update audit record if it already exists.
3183          */
3184         audit_inode(nd->name, path.dentry, 0);
3185 
3186         if (unlikely((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT))) {
3187                 path_to_nameidata(&path, nd);
3188                 return -EEXIST;
3189         }
3190 
3191         error = follow_managed(&path, nd);
3192         if (unlikely(error < 0))
3193                 return error;
3194 
3195         seq = 0;        /* out of RCU mode, so the value doesn't matter */
3196         inode = d_backing_inode(path.dentry);
3197 finish_lookup:
3198         if (nd->depth)
3199                 put_link(nd);
3200         error = should_follow_link(nd, &path, nd->flags & LOOKUP_FOLLOW,
3201                                    inode, seq);
3202         if (unlikely(error))
3203                 return error;
3204 
3205         if ((nd->flags & LOOKUP_RCU) || nd->path.mnt != path.mnt) {
3206                 path_to_nameidata(&path, nd);
3207         } else {
3208                 save_parent.dentry = nd->path.dentry;
3209                 save_parent.mnt = mntget(path.mnt);
3210                 nd->path.dentry = path.dentry;
3211 
3212         }
3213         nd->inode = inode;
3214         nd->seq = seq;
3215         /* Why this, you ask?  _Now_ we might have grown LOOKUP_JUMPED... */
3216 finish_open:
3217         error = complete_walk(nd);
3218         if (error) {
3219                 path_put(&save_parent);
3220                 return error;
3221         }
3222         audit_inode(nd->name, nd->path.dentry, 0);
3223         if (unlikely(d_is_symlink(nd->path.dentry)) && !(open_flag & O_PATH)) {
3224                 error = -ELOOP;
3225                 goto out;
3226         }
3227         error = -EISDIR;
3228         if ((open_flag & O_CREAT) && d_is_dir(nd->path.dentry))
3229                 goto out;
3230         error = -ENOTDIR;
3231         if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
3232                 goto out;
3233         if (!d_is_reg(nd->path.dentry))
3234                 will_truncate = false;
3235 
3236         if (will_truncate) {
3237                 error = mnt_want_write(nd->path.mnt);
3238                 if (error)
3239                         goto out;
3240                 got_write = true;
3241         }
3242 finish_open_created:
3243         if (likely(!(open_flag & O_PATH))) {
3244                 error = may_open(&nd->path, acc_mode, open_flag);
3245                 if (error)
3246                         goto out;
3247         }
3248         BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */
3249         error = vfs_open(&nd->path, file, current_cred());
3250         if (!error) {
3251                 *opened |= FILE_OPENED;
3252         } else {
3253                 if (error == -EOPENSTALE)
3254                         goto stale_open;
3255                 goto out;
3256         }
3257 opened:
3258         error = open_check_o_direct(file);
3259         if (error)
3260                 goto exit_fput;
3261         error = ima_file_check(file, op->acc_mode, *opened);
3262         if (error)
3263                 goto exit_fput;
3264 
3265         if (will_truncate) {
3266                 error = handle_truncate(file);
3267                 if (error)
3268                         goto exit_fput;
3269         }
3270 out:
3271         if (unlikely(error > 0)) {
3272                 WARN_ON(1);
3273                 error = -EINVAL;
3274         }
3275         if (got_write)
3276                 mnt_drop_write(nd->path.mnt);
3277         path_put(&save_parent);
3278         return error;
3279 
3280 exit_fput:
3281         fput(file);
3282         goto out;
3283 
3284 stale_open:
3285         /* If no saved parent or already retried then can't retry */
3286         if (!save_parent.dentry || retried)
3287                 goto out;
3288 
3289         BUG_ON(save_parent.dentry != dir);
3290         path_put(&nd->path);
3291         nd->path = save_parent;
3292         nd->inode = dir->d_inode;
3293         save_parent.mnt = NULL;
3294         save_parent.dentry = NULL;
3295         if (got_write) {
3296                 mnt_drop_write(nd->path.mnt);
3297                 got_write = false;
3298         }
3299         retried = true;
3300         goto retry_lookup;
3301 }
3302 
3303 static int do_tmpfile(struct nameidata *nd, unsigned flags,
3304                 const struct open_flags *op,
3305                 struct file *file, int *opened)
3306 {
3307         static const struct qstr name = QSTR_INIT("/", 1);
3308         struct dentry *child;
3309         struct inode *dir;
3310         struct path path;
3311         int error = path_lookupat(nd, flags | LOOKUP_DIRECTORY, &path);
3312         if (unlikely(error))
3313                 return error;
3314         error = mnt_want_write(path.mnt);
3315         if (unlikely(error))
3316                 goto out;
3317         dir = path.dentry->d_inode;
3318         /* we want directory to be writable */
3319         error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
3320         if (error)
3321                 goto out2;
3322         if (!dir->i_op->tmpfile) {
3323                 error = -EOPNOTSUPP;
3324                 goto out2;
3325         }
3326         child = d_alloc(path.dentry, &name);
3327         if (unlikely(!child)) {
3328                 error = -ENOMEM;
3329                 goto out2;
3330         }
3331         dput(path.dentry);
3332         path.dentry = child;
3333         error = dir->i_op->tmpfile(dir, child, op->mode);
3334         if (error)
3335                 goto out2;
3336         audit_inode(nd->name, child, 0);
3337         /* Don't check for other permissions, the inode was just created */
3338         error = may_open(&path, 0, op->open_flag);
3339         if (error)
3340                 goto out2;
3341         file->f_path.mnt = path.mnt;
3342         error = finish_open(file, child, NULL, opened);
3343         if (error)
3344                 goto out2;
3345         error = open_check_o_direct(file);
3346         if (error) {
3347                 fput(file);
3348         } else if (!(op->open_flag & O_EXCL)) {
3349                 struct inode *inode = file_inode(file);
3350                 spin_lock(&inode->i_lock);
3351                 inode->i_state |= I_LINKABLE;
3352                 spin_unlock(&inode->i_lock);
3353         }
3354 out2:
3355         mnt_drop_write(path.mnt);
3356 out:
3357         path_put(&path);
3358         return error;
3359 }
3360 
3361 static struct file *path_openat(struct nameidata *nd,
3362                         const struct open_flags *op, unsigned flags)
3363 {
3364         const char *s;
3365         struct file *file;
3366         int opened = 0;
3367         int error;
3368 
3369         file = get_empty_filp();
3370         if (IS_ERR(file))
3371                 return file;
3372 
3373         file->f_flags = op->open_flag;
3374 
3375         if (unlikely(file->f_flags & __O_TMPFILE)) {
3376                 error = do_tmpfile(nd, flags, op, file, &opened);
3377                 goto out2;
3378         }
3379 
3380         s = path_init(nd, flags);
3381         if (IS_ERR(s)) {
3382                 put_filp(file);
3383                 return ERR_CAST(s);
3384         }
3385         while (!(error = link_path_walk(s, nd)) &&
3386                 (error = do_last(nd, file, op, &opened)) > 0) {
3387                 nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
3388                 s = trailing_symlink(nd);
3389                 if (IS_ERR(s)) {
3390                         error = PTR_ERR(s);
3391                         break;
3392                 }
3393         }
3394         terminate_walk(nd);
3395 out2:
3396         if (!(opened & FILE_OPENED)) {
3397                 BUG_ON(!error);
3398                 put_filp(file);
3399         }
3400         if (unlikely(error)) {
3401                 if (error == -EOPENSTALE) {
3402                         if (flags & LOOKUP_RCU)
3403                                 error = -ECHILD;
3404                         else
3405                                 error = -ESTALE;
3406                 }
3407                 file = ERR_PTR(error);
3408         }
3409         return file;
3410 }
3411 
3412 struct file *do_filp_open(int dfd, struct filename *pathname,
3413                 const struct open_flags *op)
3414 {
3415         struct nameidata nd;
3416         int flags = op->lookup_flags;
3417         struct file *filp;
3418 
3419         set_nameidata(&nd, dfd, pathname);
3420         filp = path_openat(&nd, op, flags | LOOKUP_RCU);
3421         if (unlikely(filp == ERR_PTR(-ECHILD)))
3422                 filp = path_openat(&nd, op, flags);
3423         if (unlikely(filp == ERR_PTR(-ESTALE)))
3424                 filp = path_openat(&nd, op, flags | LOOKUP_REVAL);
3425         restore_nameidata();
3426         return filp;
3427 }
3428 
3429 struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
3430                 const char *name, const struct open_flags *op)
3431 {
3432         struct nameidata nd;
3433         struct file *file;
3434         struct filename *filename;
3435         int flags = op->lookup_flags | LOOKUP_ROOT;
3436 
3437         nd.root.mnt = mnt;
3438         nd.root.dentry = dentry;
3439 
3440         if (d_is_symlink(dentry) && op->intent & LOOKUP_OPEN)
3441                 return ERR_PTR(-ELOOP);
3442 
3443         filename = getname_kernel(name);
3444         if (IS_ERR(filename))
3445                 return ERR_CAST(filename);
3446 
3447         set_nameidata(&nd, -1, filename);
3448         file = path_openat(&nd, op, flags | LOOKUP_RCU);
3449         if (unlikely(file == ERR_PTR(-ECHILD)))
3450                 file = path_openat(&nd, op, flags);
3451         if (unlikely(file == ERR_PTR(-ESTALE)))
3452                 file = path_openat(&nd, op, flags | LOOKUP_REVAL);
3453         restore_nameidata();
3454         putname(filename);
3455         return file;
3456 }
3457 
3458 static struct dentry *filename_create(int dfd, struct filename *name,
3459                                 struct path *path, unsigned int lookup_flags)
3460 {
3461         struct dentry *dentry = ERR_PTR(-EEXIST);
3462         struct qstr last;
3463         int type;
3464         int err2;
3465         int error;
3466         bool is_dir = (lookup_flags & LOOKUP_DIRECTORY);
3467 
3468         /*
3469          * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any
3470          * other flags passed in are ignored!
3471          */
3472         lookup_flags &= LOOKUP_REVAL;
3473 
3474         name = filename_parentat(dfd, name, lookup_flags, path, &last, &type);
3475         if (IS_ERR(name))
3476                 return ERR_CAST(name);
3477 
3478         /*
3479          * Yucky last component or no last component at all?
3480          * (foo/., foo/.., /////)
3481          */
3482         if (unlikely(type != LAST_NORM))
3483                 goto out;
3484 
3485         /* don't fail immediately if it's r/o, at least try to report other errors */
3486         err2 = mnt_want_write(path->mnt);
3487         /*
3488          * Do the final lookup.
3489          */
3490         lookup_flags |= LOOKUP_CREATE | LOOKUP_EXCL;
3491         inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
3492         dentry = __lookup_hash(&last, path->dentry, lookup_flags);
3493         if (IS_ERR(dentry))
3494                 goto unlock;
3495 
3496         error = -EEXIST;
3497         if (d_is_positive(dentry))
3498                 goto fail;
3499 
3500         /*
3501          * Special case - lookup gave negative, but... we had foo/bar/
3502          * From the vfs_mknod() POV we just have a negative dentry -
3503          * all is fine. Let's be bastards - you had / on the end, you've
3504          * been asking for (non-existent) directory. -ENOENT for you.
3505          */
3506         if (unlikely(!is_dir && last.name[last.len])) {
3507                 error = -ENOENT;
3508                 goto fail;
3509         }
3510         if (unlikely(err2)) {
3511                 error = err2;
3512                 goto fail;
3513         }
3514         putname(name);
3515         return dentry;
3516 fail:
3517         dput(dentry);
3518         dentry = ERR_PTR(error);
3519 unlock:
3520         inode_unlock(path->dentry->d_inode);
3521         if (!err2)
3522                 mnt_drop_write(path->mnt);
3523 out:
3524         path_put(path);
3525         putname(name);
3526         return dentry;
3527 }
3528 
3529 struct dentry *kern_path_create(int dfd, const char *pathname,
3530                                 struct path *path, unsigned int lookup_flags)
3531 {
3532         return filename_create(dfd, getname_kernel(pathname),
3533                                 path, lookup_flags);
3534 }
3535 EXPORT_SYMBOL(kern_path_create);
3536 
3537 void done_path_create(struct path *path, struct dentry *dentry)
3538 {
3539         dput(dentry);
3540         inode_unlock(path->dentry->d_inode);
3541         mnt_drop_write(path->mnt);
3542         path_put(path);
3543 }
3544 EXPORT_SYMBOL(done_path_create);
3545 
3546 inline struct dentry *user_path_create(int dfd, const char __user *pathname,
3547                                 struct path *path, unsigned int lookup_flags)
3548 {
3549         return filename_create(dfd, getname(pathname), path, lookup_flags);
3550 }
3551 EXPORT_SYMBOL(user_path_create);
3552 
3553 int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
3554 {
3555         int error = may_create(dir, dentry);
3556 
3557         if (error)
3558                 return error;
3559 
3560         if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
3561                 return -EPERM;
3562 
3563         if (!dir->i_op->mknod)
3564                 return -EPERM;
3565 
3566         error = devcgroup_inode_mknod(mode, dev);
3567         if (error)
3568                 return error;
3569 
3570         error = security_inode_mknod(dir, dentry, mode, dev);
3571         if (error)
3572                 return error;
3573 
3574         error = dir->i_op->mknod(dir, dentry, mode, dev);
3575         if (!error)
3576                 fsnotify_create(dir, dentry);
3577         return error;
3578 }
3579 EXPORT_SYMBOL(vfs_mknod);
3580 
3581 static int may_mknod(umode_t mode)
3582 {
3583         switch (mode & S_IFMT) {
3584         case S_IFREG:
3585         case S_IFCHR:
3586         case S_IFBLK:
3587         case S_IFIFO:
3588         case S_IFSOCK:
3589         case 0: /* zero mode translates to S_IFREG */
3590                 return 0;
3591         case S_IFDIR:
3592                 return -EPERM;
3593         default:
3594                 return -EINVAL;
3595         }
3596 }
3597 
3598 SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
3599                 unsigned, dev)
3600 {
3601         struct dentry *dentry;
3602         struct path path;
3603         int error;
3604         unsigned int lookup_flags = 0;
3605 
3606         error = may_mknod(mode);
3607         if (error)
3608                 return error;
3609 retry:
3610         dentry = user_path_create(dfd, filename, &path, lookup_flags);
3611         if (IS_ERR(dentry))
3612                 return PTR_ERR(dentry);
3613 
3614         if (!IS_POSIXACL(path.dentry->d_inode))
3615                 mode &= ~current_umask();
3616         error = security_path_mknod(&path, dentry, mode, dev);
3617         if (error)
3618                 goto out;
3619         switch (mode & S_IFMT) {
3620                 case 0: case S_IFREG:
3621                         error = vfs_create(path.dentry->d_inode,dentry,mode,true);
3622                         break;
3623                 case S_IFCHR: case S_IFBLK:
3624                         error = vfs_mknod(path.dentry->d_inode,dentry,mode,
3625                                         new_decode_dev(dev));
3626                         break;
3627                 case S_IFIFO: case S_IFSOCK:
3628                         error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
3629                         break;
3630         }
3631 out:
3632         done_path_create(&path, dentry);
3633         if (retry_estale(error, lookup_flags)) {
3634                 lookup_flags |= LOOKUP_REVAL;
3635                 goto retry;
3636         }
3637         return error;
3638 }
3639 
3640 SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, dev)
3641 {
3642         return sys_mknodat(AT_FDCWD, filename, mode, dev);
3643 }
3644 
3645 int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
3646 {
3647         int error = may_create(dir, dentry);
3648         unsigned max_links = dir->i_sb->s_max_links;
3649 
3650         if (error)
3651                 return error;
3652 
3653         if (!dir->i_op->mkdir)
3654                 return -EPERM;
3655 
3656         mode &= (S_IRWXUGO|S_ISVTX);
3657         error = security_inode_mkdir(dir, dentry, mode);
3658         if (error)
3659                 return error;
3660 
3661         if (max_links && dir->i_nlink >= max_links)
3662                 return -EMLINK;
3663 
3664         error = dir->i_op->mkdir(dir, dentry, mode);
3665         if (!error)
3666                 fsnotify_mkdir(dir, dentry);
3667         return error;
3668 }
3669 EXPORT_SYMBOL(vfs_mkdir);
3670 
3671 SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
3672 {
3673         struct dentry *dentry;
3674         struct path path;
3675         int error;
3676         unsigned int lookup_flags = LOOKUP_DIRECTORY;
3677 
3678 retry:
3679         dentry = user_path_create(dfd, pathname, &path, lookup_flags);
3680         if (IS_ERR(dentry))
3681                 return PTR_ERR(dentry);
3682 
3683         if (!IS_POSIXACL(path.dentry->d_inode))
3684                 mode &= ~current_umask();
3685         error = security_path_mkdir(&path, dentry, mode);
3686         if (!error)
3687                 error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
3688         done_path_create(&path, dentry);
3689         if (retry_estale(error, lookup_flags)) {
3690                 lookup_flags |= LOOKUP_REVAL;
3691                 goto retry;
3692         }
3693         return error;
3694 }
3695 
3696 SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode)
3697 {
3698         return sys_mkdirat(AT_FDCWD, pathname, mode);
3699 }
3700 
3701 int vfs_rmdir(struct inode *dir, struct dentry *dentry)
3702 {
3703         int error = may_delete(dir, dentry, 1);
3704 
3705         if (error)
3706                 return error;
3707 
3708         if (!dir->i_op->rmdir)
3709                 return -EPERM;
3710 
3711         dget(dentry);
3712         inode_lock(dentry->d_inode);
3713 
3714         error = -EBUSY;
3715         if (is_local_mountpoint(dentry))
3716                 goto out;
3717 
3718         error = security_inode_rmdir(dir, dentry);
3719         if (error)
3720                 goto out;
3721 
3722         shrink_dcache_parent(dentry);
3723         error = dir->i_op->rmdir(dir, dentry);
3724         if (error)
3725                 goto out;
3726 
3727         dentry->d_inode->i_flags |= S_DEAD;
3728         dont_mount(dentry);
3729         detach_mounts(dentry);
3730 
3731 out:
3732         inode_unlock(dentry->d_inode);
3733         dput(dentry);
3734         if (!error)
3735                 d_delete(dentry);
3736         return error;
3737 }
3738 EXPORT_SYMBOL(vfs_rmdir);
3739 
3740 static long do_rmdir(int dfd, const char __user *pathname)
3741 {
3742         int error = 0;
3743         struct filename *name;
3744         struct dentry *dentry;
3745         struct path path;
3746         struct qstr last;
3747         int type;
3748         unsigned int lookup_flags = 0;
3749 retry:
3750         name = user_path_parent(dfd, pathname,
3751                                 &path, &last, &type, lookup_flags);
3752         if (IS_ERR(name))
3753                 return PTR_ERR(name);
3754 
3755         switch (type) {
3756         case LAST_DOTDOT:
3757                 error = -ENOTEMPTY;
3758                 goto exit1;
3759         case LAST_DOT:
3760                 error = -EINVAL;
3761                 goto exit1;
3762         case LAST_ROOT:
3763                 error = -EBUSY;
3764                 goto exit1;
3765         }
3766 
3767         error = mnt_want_write(path.mnt);
3768         if (error)
3769                 goto exit1;
3770 
3771         inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT);
3772         dentry = __lookup_hash(&last, path.dentry, lookup_flags);
3773         error = PTR_ERR(dentry);
3774         if (IS_ERR(dentry))
3775                 goto exit2;
3776         if (!dentry->d_inode) {
3777                 error = -ENOENT;
3778                 goto exit3;
3779         }
3780         error = security_path_rmdir(&path, dentry);
3781         if (error)
3782                 goto exit3;
3783         error = vfs_rmdir(path.dentry->d_inode, dentry);
3784 exit3:
3785         dput(dentry);
3786 exit2:
3787         inode_unlock(path.dentry->d_inode);
3788         mnt_drop_write(path.mnt);
3789 exit1:
3790         path_put(&path);
3791         putname(name);
3792         if (retry_estale(error, lookup_flags)) {
3793                 lookup_flags |= LOOKUP_REVAL;
3794                 goto retry;
3795         }
3796         return error;
3797 }
3798 
3799 SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
3800 {
3801         return do_rmdir(AT_FDCWD, pathname);
3802 }
3803 
3804 /**
3805  * vfs_unlink - unlink a filesystem object
3806  * @dir:        parent directory
3807  * @dentry:     victim
3808  * @delegated_inode: returns victim inode, if the inode is delegated.
3809  *
3810  * The caller must hold dir->i_mutex.
3811  *
3812  * If vfs_unlink discovers a delegation, it will return -EWOULDBLOCK and
3813  * return a reference to the inode in delegated_inode.  The caller
3814  * should then break the delegation on that inode and retry.  Because
3815  * breaking a delegation may take a long time, the caller should drop
3816  * dir->i_mutex before doing so.
3817  *
3818  * Alternatively, a caller may pass NULL for delegated_inode.  This may
3819  * be appropriate for callers that expect the underlying filesystem not
3820  * to be NFS exported.
3821  */
3822 int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode)
3823 {
3824         struct inode *target = dentry->d_inode;
3825         int error = may_delete(dir, dentry, 0);
3826 
3827         if (error)
3828                 return error;
3829 
3830         if (!dir->i_op->unlink)
3831                 return -EPERM;
3832 
3833         inode_lock(target);
3834         if (is_local_mountpoint(dentry))
3835                 error = -EBUSY;
3836         else {
3837                 error = security_inode_unlink(dir, dentry);
3838                 if (!error) {
3839                         error = try_break_deleg(target, delegated_inode);
3840                         if (error)
3841                                 goto out;
3842                         error = dir->i_op->unlink(dir, dentry);
3843                         if (!error) {
3844                                 dont_mount(dentry);
3845                                 detach_mounts(dentry);
3846                         }
3847                 }
3848         }
3849 out:
3850         inode_unlock(target);
3851 
3852         /* We don't d_delete() NFS sillyrenamed files--they still exist. */
3853         if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) {
3854                 fsnotify_link_count(target);
3855                 d_delete(dentry);
3856         }
3857 
3858         return error;
3859 }
3860 EXPORT_SYMBOL(vfs_unlink);
3861 
3862 /*
3863  * Make sure that the actual truncation of the file will occur outside its
3864  * directory's i_mutex.  Truncate can take a long time if there is a lot of
3865  * writeout happening, and we don't want to prevent access to the directory
3866  * while waiting on the I/O.
3867  */
3868 static long do_unlinkat(int dfd, const char __user *pathname)
3869 {
3870         int error;
3871         struct filename *name;
3872         struct dentry *dentry;
3873         struct path path;
3874         struct qstr last;
3875         int type;
3876         struct inode *inode = NULL;
3877         struct inode *delegated_inode = NULL;
3878         unsigned int lookup_flags = 0;
3879 retry:
3880         name = user_path_parent(dfd, pathname,
3881                                 &path, &last, &type, lookup_flags);
3882         if (IS_ERR(name))
3883                 return PTR_ERR(name);
3884 
3885         error = -EISDIR;
3886         if (type != LAST_NORM)
3887                 goto exit1;
3888 
3889         error = mnt_want_write(path.mnt);
3890         if (error)
3891                 goto exit1;
3892 retry_deleg:
3893         inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT);
3894         dentry = __lookup_hash(&last, path.dentry, lookup_flags);
3895         error = PTR_ERR(dentry);
3896         if (!IS_ERR(dentry)) {
3897                 /* Why not before? Because we want correct error value */
3898                 if (last.name[last.len])
3899                         goto slashes;
3900                 inode = dentry->d_inode;
3901                 if (d_is_negative(dentry))
3902                         goto slashes;
3903                 ihold(inode);
3904                 error = security_path_unlink(&path, dentry);
3905                 if (error)
3906                         goto exit2;
3907                 error = vfs_unlink(path.dentry->d_inode, dentry, &delegated_inode);
3908 exit2:
3909                 dput(dentry);
3910         }
3911         inode_unlock(path.dentry->d_inode);
3912         if (inode)
3913                 iput(inode);    /* truncate the inode here */
3914         inode = NULL;
3915         if (delegated_inode) {
3916                 error = break_deleg_wait(&delegated_inode);
3917                 if (!error)
3918                         goto retry_deleg;
3919         }
3920         mnt_drop_write(path.mnt);
3921 exit1:
3922         path_put(&path);
3923         putname(name);
3924         if (retry_estale(error, lookup_flags)) {
3925                 lookup_flags |= LOOKUP_REVAL;
3926                 inode = NULL;
3927                 goto retry;
3928         }
3929         return error;
3930 
3931 slashes:
3932         if (d_is_negative(dentry))
3933                 error = -ENOENT;
3934         else if (d_is_dir(dentry))
3935                 error = -EISDIR;
3936         else
3937                 error = -ENOTDIR;
3938         goto exit2;
3939 }
3940 
3941 SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag)
3942 {
3943         if ((flag & ~AT_REMOVEDIR) != 0)
3944                 return -EINVAL;
3945 
3946         if (flag & AT_REMOVEDIR)
3947                 return do_rmdir(dfd, pathname);
3948 
3949         return do_unlinkat(dfd, pathname);
3950 }
3951 
3952 SYSCALL_DEFINE1(unlink, const char __user *, pathname)
3953 {
3954         return do_unlinkat(AT_FDCWD, pathname);
3955 }
3956 
3957 int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
3958 {
3959         int error = may_create(dir, dentry);
3960 
3961         if (error)
3962                 return error;
3963 
3964         if (!dir->i_op->symlink)
3965                 return -EPERM;
3966 
3967         error = security_inode_symlink(dir, dentry, oldname);
3968         if (error)
3969                 return error;
3970 
3971         error = dir->i_op->symlink(dir, dentry, oldname);
3972         if (!error)
3973                 fsnotify_create(dir, dentry);
3974         return error;
3975 }
3976 EXPORT_SYMBOL(vfs_symlink);
3977 
3978 SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
3979                 int, newdfd, const char __user *, newname)
3980 {
3981         int error;
3982         struct filename *from;
3983         struct dentry *dentry;
3984         struct path path;
3985         unsigned int lookup_flags = 0;
3986 
3987         from = getname(oldname);
3988         if (IS_ERR(from))
3989                 return PTR_ERR(from);
3990 retry:
3991         dentry = user_path_create(newdfd, newname, &path, lookup_flags);
3992         error = PTR_ERR(dentry);
3993         if (IS_ERR(dentry))
3994                 goto out_putname;
3995 
3996         error = security_path_symlink(&path, dentry, from->name);
3997         if (!error)
3998                 error = vfs_symlink(path.dentry->d_inode, dentry, from->name);
3999         done_path_create(&path, dentry);
4000         if (retry_estale(error, lookup_flags)) {
4001                 lookup_flags |= LOOKUP_REVAL;
4002                 goto retry;
4003         }
4004 out_putname:
4005         putname(from);
4006         return error;
4007 }
4008 
4009 SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname)
4010 {
4011         return sys_symlinkat(oldname, AT_FDCWD, newname);
4012 }
4013 
4014 /**
4015  * vfs_link - create a new link
4016  * @old_dentry: object to be linked
4017  * @dir:        new parent
4018  * @new_dentry: where to create the new link
4019  * @delegated_inode: returns inode needing a delegation break
4020  *
4021  * The caller must hold dir->i_mutex
4022  *
4023  * If vfs_link discovers a delegation on the to-be-linked file in need
4024  * of breaking, it will return -EWOULDBLOCK and return a reference to the
4025  * inode in delegated_inode.  The caller should then break the delegation
4026  * and retry.  Because breaking a delegation may take a long time, the
4027  * caller should drop the i_mutex before doing so.
4028  *
4029  * Alternatively, a caller may pass NULL for delegated_inode.  This may
4030  * be appropriate for callers that expect the underlying filesystem not
4031  * to be NFS exported.
4032  */
4033 int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry, struct inode **delegated_inode)
4034 {
4035         struct inode *inode = old_dentry->d_inode;
4036         unsigned max_links = dir->i_sb->s_max_links;
4037         int error;
4038 
4039         if (!inode)
4040                 return -ENOENT;
4041 
4042         error = may_create(dir, new_dentry);
4043         if (error)
4044                 return error;
4045 
4046         if (dir->i_sb != inode->i_sb)
4047                 return -EXDEV;
4048 
4049         /*
4050          * A link to an append-only or immutable file cannot be created.
4051          */
4052         if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
4053                 return -EPERM;
4054         if (!dir->i_op->link)
4055                 return -EPERM;
4056         if (S_ISDIR(inode->i_mode))
4057                 return -EPERM;
4058 
4059         error = security_inode_link(old_dentry, dir, new_dentry);
4060         if (error)
4061                 return error;
4062 
4063         inode_lock(inode);
4064         /* Make sure we don't allow creating hardlink to an unlinked file */
4065         if (inode->i_nlink == 0 && !(inode->i_state & I_LINKABLE))
4066                 error =  -ENOENT;
4067         else if (max_links && inode->i_nlink >= max_links)
4068                 error = -EMLINK;
4069         else {
4070                 error = try_break_deleg(inode, delegated_inode);
4071                 if (!error)
4072                         error = dir->i_op->link(old_dentry, dir, new_dentry);
4073         }
4074 
4075         if (!error && (inode->i_state & I_LINKABLE)) {
4076                 spin_lock(&inode->i_lock);
4077                 inode->i_state &= ~I_LINKABLE;
4078                 spin_unlock(&inode->i_lock);
4079         }
4080         inode_unlock(inode);
4081         if (!error)
4082                 fsnotify_link(dir, inode, new_dentry);
4083         return error;
4084 }
4085 EXPORT_SYMBOL(vfs_link);
4086 
4087 /*
4088  * Hardlinks are often used in delicate situations.  We avoid
4089  * security-related surprises by not following symlinks on the
4090  * newname.  --KAB
4091  *
4092  * We don't follow them on the oldname either to be compatible
4093  * with linux 2.0, and to avoid hard-linking to directories
4094  * and other special files.  --ADM
4095  */
4096 SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
4097                 int, newdfd, const char __user *, newname, int, flags)
4098 {
4099         struct dentry *new_dentry;
4100         struct path old_path, new_path;
4101         struct inode *delegated_inode = NULL;
4102         int how = 0;
4103         int error;
4104 
4105         if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
4106                 return -EINVAL;
4107         /*
4108          * To use null names we require CAP_DAC_READ_SEARCH
4109          * This ensures that not everyone will be able to create
4110          * handlink using the passed filedescriptor.
4111          */
4112         if (flags & AT_EMPTY_PATH) {
4113                 if (!capable(CAP_DAC_READ_SEARCH))
4114                         return -ENOENT;
4115                 how = LOOKUP_EMPTY;
4116         }
4117 
4118         if (flags & AT_SYMLINK_FOLLOW)
4119                 how |= LOOKUP_FOLLOW;
4120 retry:
4121         error = user_path_at(olddfd, oldname, how, &old_path);
4122         if (error)
4123                 return error;
4124 
4125         new_dentry = user_path_create(newdfd, newname, &new_path,
4126                                         (how & LOOKUP_REVAL));
4127         error = PTR_ERR(new_dentry);
4128         if (IS_ERR(new_dentry))
4129                 goto out;
4130 
4131         error = -EXDEV;
4132         if (old_path.mnt != new_path.mnt)
4133                 goto out_dput;
4134         error = may_linkat(&old_path);
4135         if (unlikely(error))
4136                 goto out_dput;
4137         error = security_path_link(old_path.dentry, &new_path, new_dentry);
4138         if (error)
4139                 goto out_dput;
4140         error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry, &delegated_inode);
4141 out_dput:
4142         done_path_create(&new_path, new_dentry);
4143         if (delegated_inode) {
4144                 error = break_deleg_wait(&delegated_inode);
4145                 if (!error) {
4146                         path_put(&old_path);
4147                         goto retry;
4148                 }
4149         }
4150         if (retry_estale(error, how)) {
4151                 path_put(&old_path);
4152                 how |= LOOKUP_REVAL;
4153                 goto retry;
4154         }
4155 out:
4156         path_put(&old_path);
4157 
4158         return error;
4159 }
4160 
4161 SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
4162 {
4163         return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
4164 }
4165 
4166 /**
4167  * vfs_rename - rename a filesystem object
4168  * @old_dir:    parent of source
4169  * @old_dentry: source
4170  * @new_dir:    parent of destination
4171  * @new_dentry: destination
4172  * @delegated_inode: returns an inode needing a delegation break
4173  * @flags:      rename flags
4174  *
4175  * The caller must hold multiple mutexes--see lock_rename()).
4176  *
4177  * If vfs_rename discovers a delegation in need of breaking at either
4178  * the source or destination, it will return -EWOULDBLOCK and return a
4179  * reference to the inode in delegated_inode.  The caller should then
4180  * break the delegation and retry.  Because breaking a delegation may
4181  * take a long time, the caller should drop all locks before doing
4182  * so.
4183  *
4184  * Alternatively, a caller may pass NULL for delegated_inode.  This may
4185  * be appropriate for callers that expect the underlying filesystem not
4186  * to be NFS exported.
4187  *
4188  * The worst of all namespace operations - renaming directory. "Perverted"
4189  * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
4190  * Problems:
4191  *      a) we can get into loop creation.
4192  *      b) race potential - two innocent renames can create a loop together.
4193  *         That's where 4.4 screws up. Current fix: serialization on
4194  *         sb->s_vfs_rename_mutex. We might be more accurate, but that's another
4195  *         story.
4196  *      c) we have to lock _four_ objects - parents and victim (if it exists),
4197  *         and source (if it is not a directory).
4198  *         And that - after we got ->i_mutex on parents (until then we don't know
4199  *         whether the target exists).  Solution: try to be smart with locking
4200  *         order for inodes.  We rely on the fact that tree topology may change
4201  *         only under ->s_vfs_rename_mutex _and_ that parent of the object we
4202  *         move will be locked.  Thus we can rank directories by the tree
4203  *         (ancestors first) and rank all non-directories after them.
4204  *         That works since everybody except rename does "lock parent, lookup,
4205  *         lock child" and rename is under ->s_vfs_rename_mutex.
4206  *         HOWEVER, it relies on the assumption that any object with ->lookup()
4207  *         has no more than 1 dentry.  If "hybrid" objects will ever appear,
4208  *         we'd better make sure that there's no link(2) for them.
4209  *      d) conversion from fhandle to dentry may come in the wrong moment - when
4210  *         we are removing the target. Solution: we will have to grab ->i_mutex
4211  *         in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
4212  *         ->i_mutex on parents, which works but leads to some truly excessive
4213  *         locking].
4214  */
4215 int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
4216                struct inode *new_dir, struct dentry *new_dentry,
4217                struct inode **delegated_inode, unsigned int flags)
4218 {
4219         int error;
4220         bool is_dir = d_is_dir(old_dentry);
4221         const unsigned char *old_name;
4222         struct inode *source = old_dentry->d_inode;
4223         struct inode *target = new_dentry->d_inode;
4224         bool new_is_dir = false;
4225         unsigned max_links = new_dir->i_sb->s_max_links;
4226 
4227         /*
4228          * Check source == target.
4229          * On overlayfs need to look at underlying inodes.
4230          */
4231         if (vfs_select_inode(old_dentry, 0) == vfs_select_inode(new_dentry, 0))
4232                 return 0;
4233 
4234         error = may_delete(old_dir, old_dentry, is_dir);
4235         if (error)
4236                 return error;
4237 
4238         if (!target) {
4239                 error = may_create(new_dir, new_dentry);
4240         } else {
4241                 new_is_dir = d_is_dir(new_dentry);
4242 
4243                 if (!(flags & RENAME_EXCHANGE))
4244                         error = may_delete(new_dir, new_dentry, is_dir);
4245                 else
4246                         error = may_delete(new_dir, new_dentry, new_is_dir);
4247         }
4248         if (error)
4249                 return error;
4250 
4251         if (!old_dir->i_op->rename && !old_dir->i_op->rename2)
4252                 return -EPERM;
4253 
4254         if (flags && !old_dir->i_op->rename2)
4255                 return -EINVAL;
4256 
4257         /*
4258          * If we are going to change the parent - check write permissions,
4259          * we'll need to flip '..'.
4260          */
4261         if (new_dir != old_dir) {
4262                 if (is_dir) {
4263                         error = inode_permission(source, MAY_WRITE);
4264                         if (error)
4265                                 return error;
4266                 }
4267                 if ((flags & RENAME_EXCHANGE) && new_is_dir) {
4268                         error = inode_permission(target, MAY_WRITE);
4269                         if (error)
4270                                 return error;
4271                 }
4272         }
4273 
4274         error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry,
4275                                       flags);
4276         if (error)
4277                 return error;
4278 
4279         old_name = fsnotify_oldname_init(old_dentry->d_name.name);
4280         dget(new_dentry);
4281         if (!is_dir || (flags & RENAME_EXCHANGE))
4282                 lock_two_nondirectories(source, target);
4283         else if (target)
4284                 inode_lock(target);
4285 
4286         error = -EBUSY;
4287         if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
4288                 goto out;
4289 
4290         if (max_links && new_dir != old_dir) {
4291                 error = -EMLINK;
4292                 if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
4293                         goto out;
4294                 if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
4295                     old_dir->i_nlink >= max_links)
4296                         goto out;
4297         }
4298         if (is_dir && !(flags & RENAME_EXCHANGE) && target)
4299                 shrink_dcache_parent(new_dentry);
4300         if (!is_dir) {
4301                 error = try_break_deleg(source, delegated_inode);
4302                 if (error)
4303                         goto out;
4304         }
4305         if (target && !new_is_dir) {
4306                 error = try_break_deleg(target, delegated_inode);
4307                 if (error)
4308                         goto out;
4309         }
4310         if (!old_dir->i_op->rename2) {
4311                 error = old_dir->i_op->rename(old_dir, old_dentry,
4312                                               new_dir, new_dentry);
4313         } else {
4314                 WARN_ON(old_dir->i_op->rename != NULL);
4315                 error = old_dir->i_op->rename2(old_dir, old_dentry,
4316                                                new_dir, new_dentry, flags);
4317         }
4318         if (error)
4319                 goto out;
4320 
4321         if (!(flags & RENAME_EXCHANGE) && target) {
4322                 if (is_dir)
4323                         target->i_flags |= S_DEAD;
4324                 dont_mount(new_dentry);
4325                 detach_mounts(new_dentry);
4326         }
4327         if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
4328                 if (!(flags & RENAME_EXCHANGE))
4329                         d_move(old_dentry, new_dentry);
4330                 else
4331                         d_exchange(old_dentry, new_dentry);
4332         }
4333 out:
4334         if (!is_dir || (flags & RENAME_EXCHANGE))
4335                 unlock_two_nondirectories(source, target);
4336         else if (target)
4337                 inode_unlock(target);
4338         dput(new_dentry);
4339         if (!error) {
4340                 fsnotify_move(old_dir, new_dir, old_name, is_dir,
4341                               !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
4342                 if (flags & RENAME_EXCHANGE) {
4343                         fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
4344                                       new_is_dir, NULL, new_dentry);
4345                 }
4346         }
4347         fsnotify_oldname_free(old_name);
4348 
4349         return error;
4350 }
4351 EXPORT_SYMBOL(vfs_rename);
4352 
4353 SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname,
4354                 int, newdfd, const char __user *, newname, unsigned int, flags)
4355 {
4356         struct dentry *old_dentry, *new_dentry;
4357         struct dentry *trap;
4358         struct path old_path, new_path;
4359         struct qstr old_last, new_last;
4360         int old_type, new_type;
4361         struct inode *delegated_inode = NULL;
4362         struct filename *from;
4363         struct filename *to;
4364         unsigned int lookup_flags = 0, target_flags = LOOKUP_RENAME_TARGET;
4365         bool should_retry = false;
4366         int error;
4367 
4368         if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
4369                 return -EINVAL;
4370 
4371         if ((flags & (RENAME_NOREPLACE | RENAME_WHITEOUT)) &&
4372             (flags & RENAME_EXCHANGE))
4373                 return -EINVAL;
4374 
4375         if ((flags & RENAME_WHITEOUT) && !capable(CAP_MKNOD))
4376                 return -EPERM;
4377 
4378         if (flags & RENAME_EXCHANGE)
4379                 target_flags = 0;
4380 
4381 retry:
4382         from = user_path_parent(olddfd, oldname,
4383                                 &old_path, &old_last, &old_type, lookup_flags);
4384         if (IS_ERR(from)) {
4385                 error = PTR_ERR(from);
4386                 goto exit;
4387         }
4388 
4389         to = user_path_parent(newdfd, newname,
4390                                 &new_path, &new_last, &new_type, lookup_flags);
4391         if (IS_ERR(to)) {
4392                 error = PTR_ERR(to);
4393                 goto exit1;
4394         }
4395 
4396         error = -EXDEV;
4397         if (old_path.mnt != new_path.mnt)
4398                 goto exit2;
4399 
4400         error = -EBUSY;
4401         if (old_type != LAST_NORM)
4402                 goto exit2;
4403 
4404         if (flags & RENAME_NOREPLACE)
4405                 error = -EEXIST;
4406         if (new_type != LAST_NORM)
4407                 goto exit2;
4408 
4409         error = mnt_want_write(old_path.mnt);
4410         if (error)
4411                 goto exit2;
4412 
4413 retry_deleg:
4414         trap = lock_rename(new_path.dentry, old_path.dentry);
4415 
4416         old_dentry = __lookup_hash(&old_last, old_path.dentry, lookup_flags);
4417         error = PTR_ERR(old_dentry);
4418         if (IS_ERR(old_dentry))
4419                 goto exit3;
4420         /* source must exist */
4421         error = -ENOENT;
4422         if (d_is_negative(old_dentry))
4423                 goto exit4;
4424         new_dentry = __lookup_hash(&new_last, new_path.dentry, lookup_flags | target_flags);
4425         error = PTR_ERR(new_dentry);
4426         if (IS_ERR(new_dentry))
4427                 goto exit4;
4428         error = -EEXIST;
4429         if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
4430                 goto exit5;
4431         if (flags & RENAME_EXCHANGE) {
4432                 error = -ENOENT;
4433                 if (d_is_negative(new_dentry))
4434                         goto exit5;
4435 
4436                 if (!d_is_dir(new_dentry)) {
4437                         error = -ENOTDIR;
4438                         if (new_last.name[new_last.len])
4439                                 goto exit5;
4440                 }
4441         }
4442         /* unless the source is a directory trailing slashes give -ENOTDIR */
4443         if (!d_is_dir(old_dentry)) {
4444                 error = -ENOTDIR;
4445                 if (old_last.name[old_last.len])
4446                         goto exit5;
4447                 if (!(flags & RENAME_EXCHANGE) && new_last.name[new_last.len])
4448                         goto exit5;
4449         }
4450         /* source should not be ancestor of target */
4451         error = -EINVAL;
4452         if (old_dentry == trap)
4453                 goto exit5;
4454         /* target should not be an ancestor of source */
4455         if (!(flags & RENAME_EXCHANGE))
4456                 error = -ENOTEMPTY;
4457         if (new_dentry == trap)
4458                 goto exit5;
4459 
4460         error = security_path_rename(&old_path, old_dentry,
4461                                      &new_path, new_dentry, flags);
4462         if (error)
4463                 goto exit5;
4464         error = vfs_rename(old_path.dentry->d_inode, old_dentry,
4465                            new_path.dentry->d_inode, new_dentry,
4466                            &delegated_inode, flags);
4467 exit5:
4468         dput(new_dentry);
4469 exit4:
4470         dput(old_dentry);
4471 exit3:
4472         unlock_rename(new_path.dentry, old_path.dentry);
4473         if (delegated_inode) {
4474                 error = break_deleg_wait(&delegated_inode);
4475                 if (!error)
4476                         goto retry_deleg;
4477         }
4478         mnt_drop_write(old_path.mnt);
4479 exit2:
4480         if (retry_estale(error, lookup_flags))
4481                 should_retry = true;
4482         path_put(&new_path);
4483         putname(to);
4484 exit1:
4485         path_put(&old_path);
4486         putname(from);
4487         if (should_retry) {
4488                 should_retry = false;
4489                 lookup_flags |= LOOKUP_REVAL;
4490                 goto retry;
4491         }
4492 exit:
4493         return error;
4494 }
4495 
4496 SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
4497                 int, newdfd, const char __user *, newname)
4498 {
4499         return sys_renameat2(olddfd, oldname, newdfd, newname, 0);
4500 }
4501 
4502 SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newname)
4503 {
4504         return sys_renameat2(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
4505 }
4506 
4507 int vfs_whiteout(struct inode *dir, struct dentry *dentry)
4508 {
4509         int error = may_create(dir, dentry);
4510         if (error)
4511                 return error;
4512 
4513         if (!dir->i_op->mknod)
4514                 return -EPERM;
4515 
4516         return dir->i_op->mknod(dir, dentry,
4517                                 S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
4518 }
4519 EXPORT_SYMBOL(vfs_whiteout);
4520 
4521 int readlink_copy(char __user *buffer, int buflen, const char *link)
4522 {
4523         int len = PTR_ERR(link);
4524         if (IS_ERR(link))
4525                 goto out;
4526 
4527         len = strlen(link);
4528         if (len > (unsigned) buflen)
4529                 len = buflen;
4530         if (copy_to_user(buffer, link, len))
4531                 len = -EFAULT;
4532 out:
4533         return len;
4534 }
4535 EXPORT_SYMBOL(readlink_copy);
4536 
4537 /*
4538  * A helper for ->readlink().  This should be used *ONLY* for symlinks that
4539  * have ->get_link() not calling nd_jump_link().  Using (or not using) it
4540  * for any given inode is up to filesystem.
4541  */
4542 int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
4543 {
4544         DEFINE_DELAYED_CALL(done);
4545         struct inode *inode = d_inode(dentry);
4546         const char *link = inode->i_link;
4547         int res;
4548 
4549         if (!link) {
4550                 link = inode->i_op->get_link(dentry, inode, &done);
4551                 if (IS_ERR(link))
4552                         return PTR_ERR(link);
4553         }
4554         res = readlink_copy(buffer, buflen, link);
4555         do_delayed_call(&done);
4556         return res;
4557 }
4558 EXPORT_SYMBOL(generic_readlink);
4559 
4560 /* get the link contents into pagecache */
4561 const char *page_get_link(struct dentry *dentry, struct inode *inode,
4562                           struct delayed_call *callback)
4563 {
4564         char *kaddr;
4565         struct page *page;
4566         struct address_space *mapping = inode->i_mapping;
4567 
4568         if (!dentry) {
4569                 page = find_get_page(mapping, 0);
4570                 if (!page)
4571                         return ERR_PTR(-ECHILD);
4572                 if (!PageUptodate(page)) {
4573                         put_page(page);
4574                         return ERR_PTR(-ECHILD);
4575                 }
4576         } else {
4577                 page = read_mapping_page(mapping, 0, NULL);
4578                 if (IS_ERR(page))
4579                         return (char*)page;
4580         }
4581         set_delayed_call(callback, page_put_link, page);
4582         BUG_ON(mapping_gfp_mask(mapping) & __GFP_HIGHMEM);
4583         kaddr = page_address(page);
4584         nd_terminate_link(kaddr, inode->i_size, PAGE_SIZE - 1);
4585         return kaddr;
4586 }
4587 
4588 EXPORT_SYMBOL(page_get_link);
4589 
4590 void page_put_link(void *arg)
4591 {
4592         put_page(arg);
4593 }
4594 EXPORT_SYMBOL(page_put_link);
4595 
4596 int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)
4597 {
4598         DEFINE_DELAYED_CALL(done);
4599         int res = readlink_copy(buffer, buflen,
4600                                 page_get_link(dentry, d_inode(dentry),
4601                                               &done));
4602         do_delayed_call(&done);
4603         return res;
4604 }
4605 EXPORT_SYMBOL(page_readlink);
4606 
4607 /*
4608  * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS
4609  */
4610 int __page_symlink(struct inode *inode, const char *symname, int len, int nofs)
4611 {
4612         struct address_space *mapping = inode->i_mapping;
4613         struct page *page;
4614         void *fsdata;
4615         int err;
4616         unsigned int flags = AOP_FLAG_UNINTERRUPTIBLE;
4617         if (nofs)
4618                 flags |= AOP_FLAG_NOFS;
4619 
4620 retry:
4621         err = pagecache_write_begin(NULL, mapping, 0, len-1,
4622                                 flags, &page, &fsdata);
4623         if (err)
4624                 goto fail;
4625 
4626         memcpy(page_address(page), symname, len-1);
4627 
4628         err = pagecache_write_end(NULL, mapping, 0, len-1, len-1,
4629                                                         page, fsdata);
4630         if (err < 0)
4631                 goto fail;
4632         if (err < len-1)
4633                 goto retry;
4634 
4635         mark_inode_dirty(inode);
4636         return 0;
4637 fail:
4638         return err;
4639 }
4640 EXPORT_SYMBOL(__page_symlink);
4641 
4642 int page_symlink(struct inode *inode, const char *symname, int len)
4643 {
4644         return __page_symlink(inode, symname, len,
4645                         !mapping_gfp_constraint(inode->i_mapping, __GFP_FS));
4646 }
4647 EXPORT_SYMBOL(page_symlink);
4648 
4649 const struct inode_operations page_symlink_inode_operations = {
4650         .readlink       = generic_readlink,
4651         .get_link       = page_get_link,
4652 };
4653 EXPORT_SYMBOL(page_symlink_inode_operations);
4654 

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