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

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