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Linux/fs/devpts/inode.c

  1 /* -*- linux-c -*- --------------------------------------------------------- *
  2  *
  3  * linux/fs/devpts/inode.c
  4  *
  5  *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
  6  *
  7  * This file is part of the Linux kernel and is made available under
  8  * the terms of the GNU General Public License, version 2, or at your
  9  * option, any later version, incorporated herein by reference.
 10  *
 11  * ------------------------------------------------------------------------- */
 12 
 13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 14 
 15 #include <linux/module.h>
 16 #include <linux/init.h>
 17 #include <linux/fs.h>
 18 #include <linux/sched.h>
 19 #include <linux/namei.h>
 20 #include <linux/slab.h>
 21 #include <linux/mount.h>
 22 #include <linux/tty.h>
 23 #include <linux/mutex.h>
 24 #include <linux/magic.h>
 25 #include <linux/idr.h>
 26 #include <linux/devpts_fs.h>
 27 #include <linux/parser.h>
 28 #include <linux/fsnotify.h>
 29 #include <linux/seq_file.h>
 30 
 31 #define DEVPTS_DEFAULT_MODE 0600
 32 /*
 33  * ptmx is a new node in /dev/pts and will be unused in legacy (single-
 34  * instance) mode. To prevent surprises in user space, set permissions of
 35  * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
 36  * permissions.
 37  */
 38 #define DEVPTS_DEFAULT_PTMX_MODE 0000
 39 #define PTMX_MINOR      2
 40 
 41 /*
 42  * sysctl support for setting limits on the number of Unix98 ptys allocated.
 43  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
 44  */
 45 static int pty_limit = NR_UNIX98_PTY_DEFAULT;
 46 static int pty_reserve = NR_UNIX98_PTY_RESERVE;
 47 static int pty_limit_min;
 48 static int pty_limit_max = INT_MAX;
 49 static int pty_count;
 50 
 51 static struct ctl_table pty_table[] = {
 52         {
 53                 .procname       = "max",
 54                 .maxlen         = sizeof(int),
 55                 .mode           = 0644,
 56                 .data           = &pty_limit,
 57                 .proc_handler   = proc_dointvec_minmax,
 58                 .extra1         = &pty_limit_min,
 59                 .extra2         = &pty_limit_max,
 60         }, {
 61                 .procname       = "reserve",
 62                 .maxlen         = sizeof(int),
 63                 .mode           = 0644,
 64                 .data           = &pty_reserve,
 65                 .proc_handler   = proc_dointvec_minmax,
 66                 .extra1         = &pty_limit_min,
 67                 .extra2         = &pty_limit_max,
 68         }, {
 69                 .procname       = "nr",
 70                 .maxlen         = sizeof(int),
 71                 .mode           = 0444,
 72                 .data           = &pty_count,
 73                 .proc_handler   = proc_dointvec,
 74         },
 75         {}
 76 };
 77 
 78 static struct ctl_table pty_kern_table[] = {
 79         {
 80                 .procname       = "pty",
 81                 .mode           = 0555,
 82                 .child          = pty_table,
 83         },
 84         {}
 85 };
 86 
 87 static struct ctl_table pty_root_table[] = {
 88         {
 89                 .procname       = "kernel",
 90                 .mode           = 0555,
 91                 .child          = pty_kern_table,
 92         },
 93         {}
 94 };
 95 
 96 static DEFINE_MUTEX(allocated_ptys_lock);
 97 
 98 static struct vfsmount *devpts_mnt;
 99 
100 struct pts_mount_opts {
101         int setuid;
102         int setgid;
103         kuid_t   uid;
104         kgid_t   gid;
105         umode_t mode;
106         umode_t ptmxmode;
107         int newinstance;
108         int max;
109 };
110 
111 enum {
112         Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,  Opt_max,
113         Opt_err
114 };
115 
116 static const match_table_t tokens = {
117         {Opt_uid, "uid=%u"},
118         {Opt_gid, "gid=%u"},
119         {Opt_mode, "mode=%o"},
120 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
121         {Opt_ptmxmode, "ptmxmode=%o"},
122         {Opt_newinstance, "newinstance"},
123         {Opt_max, "max=%d"},
124 #endif
125         {Opt_err, NULL}
126 };
127 
128 struct pts_fs_info {
129         struct ida allocated_ptys;
130         struct pts_mount_opts mount_opts;
131         struct dentry *ptmx_dentry;
132 };
133 
134 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
135 {
136         return sb->s_fs_info;
137 }
138 
139 static inline struct super_block *pts_sb_from_inode(struct inode *inode)
140 {
141 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
142         if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
143                 return inode->i_sb;
144 #endif
145         if (!devpts_mnt)
146                 return NULL;
147         return devpts_mnt->mnt_sb;
148 }
149 
150 #define PARSE_MOUNT     0
151 #define PARSE_REMOUNT   1
152 
153 /*
154  * parse_mount_options():
155  *      Set @opts to mount options specified in @data. If an option is not
156  *      specified in @data, set it to its default value. The exception is
157  *      'newinstance' option which can only be set/cleared on a mount (i.e.
158  *      cannot be changed during remount).
159  *
160  * Note: @data may be NULL (in which case all options are set to default).
161  */
162 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
163 {
164         char *p;
165         kuid_t uid;
166         kgid_t gid;
167 
168         opts->setuid  = 0;
169         opts->setgid  = 0;
170         opts->uid     = GLOBAL_ROOT_UID;
171         opts->gid     = GLOBAL_ROOT_GID;
172         opts->mode    = DEVPTS_DEFAULT_MODE;
173         opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
174         opts->max     = NR_UNIX98_PTY_MAX;
175 
176         /* newinstance makes sense only on initial mount */
177         if (op == PARSE_MOUNT)
178                 opts->newinstance = 0;
179 
180         while ((p = strsep(&data, ",")) != NULL) {
181                 substring_t args[MAX_OPT_ARGS];
182                 int token;
183                 int option;
184 
185                 if (!*p)
186                         continue;
187 
188                 token = match_token(p, tokens, args);
189                 switch (token) {
190                 case Opt_uid:
191                         if (match_int(&args[0], &option))
192                                 return -EINVAL;
193                         uid = make_kuid(current_user_ns(), option);
194                         if (!uid_valid(uid))
195                                 return -EINVAL;
196                         opts->uid = uid;
197                         opts->setuid = 1;
198                         break;
199                 case Opt_gid:
200                         if (match_int(&args[0], &option))
201                                 return -EINVAL;
202                         gid = make_kgid(current_user_ns(), option);
203                         if (!gid_valid(gid))
204                                 return -EINVAL;
205                         opts->gid = gid;
206                         opts->setgid = 1;
207                         break;
208                 case Opt_mode:
209                         if (match_octal(&args[0], &option))
210                                 return -EINVAL;
211                         opts->mode = option & S_IALLUGO;
212                         break;
213 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
214                 case Opt_ptmxmode:
215                         if (match_octal(&args[0], &option))
216                                 return -EINVAL;
217                         opts->ptmxmode = option & S_IALLUGO;
218                         break;
219                 case Opt_newinstance:
220                         /* newinstance makes sense only on initial mount */
221                         if (op == PARSE_MOUNT)
222                                 opts->newinstance = 1;
223                         break;
224                 case Opt_max:
225                         if (match_int(&args[0], &option) ||
226                             option < 0 || option > NR_UNIX98_PTY_MAX)
227                                 return -EINVAL;
228                         opts->max = option;
229                         break;
230 #endif
231                 default:
232                         pr_err("called with bogus options\n");
233                         return -EINVAL;
234                 }
235         }
236 
237         return 0;
238 }
239 
240 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
241 static int mknod_ptmx(struct super_block *sb)
242 {
243         int mode;
244         int rc = -ENOMEM;
245         struct dentry *dentry;
246         struct inode *inode;
247         struct dentry *root = sb->s_root;
248         struct pts_fs_info *fsi = DEVPTS_SB(sb);
249         struct pts_mount_opts *opts = &fsi->mount_opts;
250         kuid_t root_uid;
251         kgid_t root_gid;
252 
253         root_uid = make_kuid(current_user_ns(), 0);
254         root_gid = make_kgid(current_user_ns(), 0);
255         if (!uid_valid(root_uid) || !gid_valid(root_gid))
256                 return -EINVAL;
257 
258         mutex_lock(&d_inode(root)->i_mutex);
259 
260         /* If we have already created ptmx node, return */
261         if (fsi->ptmx_dentry) {
262                 rc = 0;
263                 goto out;
264         }
265 
266         dentry = d_alloc_name(root, "ptmx");
267         if (!dentry) {
268                 pr_err("Unable to alloc dentry for ptmx node\n");
269                 goto out;
270         }
271 
272         /*
273          * Create a new 'ptmx' node in this mount of devpts.
274          */
275         inode = new_inode(sb);
276         if (!inode) {
277                 pr_err("Unable to alloc inode for ptmx node\n");
278                 dput(dentry);
279                 goto out;
280         }
281 
282         inode->i_ino = 2;
283         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
284 
285         mode = S_IFCHR|opts->ptmxmode;
286         init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
287         inode->i_uid = root_uid;
288         inode->i_gid = root_gid;
289 
290         d_add(dentry, inode);
291 
292         fsi->ptmx_dentry = dentry;
293         rc = 0;
294 out:
295         mutex_unlock(&d_inode(root)->i_mutex);
296         return rc;
297 }
298 
299 static void update_ptmx_mode(struct pts_fs_info *fsi)
300 {
301         struct inode *inode;
302         if (fsi->ptmx_dentry) {
303                 inode = d_inode(fsi->ptmx_dentry);
304                 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
305         }
306 }
307 #else
308 static inline void update_ptmx_mode(struct pts_fs_info *fsi)
309 {
310         return;
311 }
312 #endif
313 
314 static int devpts_remount(struct super_block *sb, int *flags, char *data)
315 {
316         int err;
317         struct pts_fs_info *fsi = DEVPTS_SB(sb);
318         struct pts_mount_opts *opts = &fsi->mount_opts;
319 
320         sync_filesystem(sb);
321         err = parse_mount_options(data, PARSE_REMOUNT, opts);
322 
323         /*
324          * parse_mount_options() restores options to default values
325          * before parsing and may have changed ptmxmode. So, update the
326          * mode in the inode too. Bogus options don't fail the remount,
327          * so do this even on error return.
328          */
329         update_ptmx_mode(fsi);
330 
331         return err;
332 }
333 
334 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
335 {
336         struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
337         struct pts_mount_opts *opts = &fsi->mount_opts;
338 
339         if (opts->setuid)
340                 seq_printf(seq, ",uid=%u",
341                            from_kuid_munged(&init_user_ns, opts->uid));
342         if (opts->setgid)
343                 seq_printf(seq, ",gid=%u",
344                            from_kgid_munged(&init_user_ns, opts->gid));
345         seq_printf(seq, ",mode=%03o", opts->mode);
346 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
347         seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
348         if (opts->max < NR_UNIX98_PTY_MAX)
349                 seq_printf(seq, ",max=%d", opts->max);
350 #endif
351 
352         return 0;
353 }
354 
355 static const struct super_operations devpts_sops = {
356         .statfs         = simple_statfs,
357         .remount_fs     = devpts_remount,
358         .show_options   = devpts_show_options,
359 };
360 
361 static void *new_pts_fs_info(void)
362 {
363         struct pts_fs_info *fsi;
364 
365         fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
366         if (!fsi)
367                 return NULL;
368 
369         ida_init(&fsi->allocated_ptys);
370         fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
371         fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
372 
373         return fsi;
374 }
375 
376 static int
377 devpts_fill_super(struct super_block *s, void *data, int silent)
378 {
379         struct inode *inode;
380 
381         s->s_blocksize = 1024;
382         s->s_blocksize_bits = 10;
383         s->s_magic = DEVPTS_SUPER_MAGIC;
384         s->s_op = &devpts_sops;
385         s->s_time_gran = 1;
386 
387         s->s_fs_info = new_pts_fs_info();
388         if (!s->s_fs_info)
389                 goto fail;
390 
391         inode = new_inode(s);
392         if (!inode)
393                 goto fail;
394         inode->i_ino = 1;
395         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
396         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
397         inode->i_op = &simple_dir_inode_operations;
398         inode->i_fop = &simple_dir_operations;
399         set_nlink(inode, 2);
400 
401         s->s_root = d_make_root(inode);
402         if (s->s_root)
403                 return 0;
404 
405         pr_err("get root dentry failed\n");
406 
407 fail:
408         return -ENOMEM;
409 }
410 
411 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
412 static int compare_init_pts_sb(struct super_block *s, void *p)
413 {
414         if (devpts_mnt)
415                 return devpts_mnt->mnt_sb == s;
416         return 0;
417 }
418 
419 /*
420  * devpts_mount()
421  *
422  *     If the '-o newinstance' mount option was specified, mount a new
423  *     (private) instance of devpts.  PTYs created in this instance are
424  *     independent of the PTYs in other devpts instances.
425  *
426  *     If the '-o newinstance' option was not specified, mount/remount the
427  *     initial kernel mount of devpts.  This type of mount gives the
428  *     legacy, single-instance semantics.
429  *
430  *     The 'newinstance' option is needed to support multiple namespace
431  *     semantics in devpts while preserving backward compatibility of the
432  *     current 'single-namespace' semantics. i.e all mounts of devpts
433  *     without the 'newinstance' mount option should bind to the initial
434  *     kernel mount, like mount_single().
435  *
436  *     Mounts with 'newinstance' option create a new, private namespace.
437  *
438  *     NOTE:
439  *
440  *     For single-mount semantics, devpts cannot use mount_single(),
441  *     because mount_single()/sget() find and use the super-block from
442  *     the most recent mount of devpts. But that recent mount may be a
443  *     'newinstance' mount and mount_single() would pick the newinstance
444  *     super-block instead of the initial super-block.
445  */
446 static struct dentry *devpts_mount(struct file_system_type *fs_type,
447         int flags, const char *dev_name, void *data)
448 {
449         int error;
450         struct pts_mount_opts opts;
451         struct super_block *s;
452 
453         error = parse_mount_options(data, PARSE_MOUNT, &opts);
454         if (error)
455                 return ERR_PTR(error);
456 
457         /* Require newinstance for all user namespace mounts to ensure
458          * the mount options are not changed.
459          */
460         if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
461                 return ERR_PTR(-EINVAL);
462 
463         if (opts.newinstance)
464                 s = sget(fs_type, NULL, set_anon_super, flags, NULL);
465         else
466                 s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
467                          NULL);
468 
469         if (IS_ERR(s))
470                 return ERR_CAST(s);
471 
472         if (!s->s_root) {
473                 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
474                 if (error)
475                         goto out_undo_sget;
476                 s->s_flags |= MS_ACTIVE;
477         }
478 
479         memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
480 
481         error = mknod_ptmx(s);
482         if (error)
483                 goto out_undo_sget;
484 
485         return dget(s->s_root);
486 
487 out_undo_sget:
488         deactivate_locked_super(s);
489         return ERR_PTR(error);
490 }
491 
492 #else
493 /*
494  * This supports only the legacy single-instance semantics (no
495  * multiple-instance semantics)
496  */
497 static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
498                 const char *dev_name, void *data)
499 {
500         return mount_single(fs_type, flags, data, devpts_fill_super);
501 }
502 #endif
503 
504 static void devpts_kill_sb(struct super_block *sb)
505 {
506         struct pts_fs_info *fsi = DEVPTS_SB(sb);
507 
508         ida_destroy(&fsi->allocated_ptys);
509         kfree(fsi);
510         kill_litter_super(sb);
511 }
512 
513 static struct file_system_type devpts_fs_type = {
514         .name           = "devpts",
515         .mount          = devpts_mount,
516         .kill_sb        = devpts_kill_sb,
517 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
518         .fs_flags       = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT,
519 #endif
520 };
521 
522 /*
523  * The normal naming convention is simply /dev/pts/<number>; this conforms
524  * to the System V naming convention
525  */
526 
527 int devpts_new_index(struct inode *ptmx_inode)
528 {
529         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
530         struct pts_fs_info *fsi;
531         int index;
532         int ida_ret;
533 
534         if (!sb)
535                 return -ENODEV;
536 
537         fsi = DEVPTS_SB(sb);
538 retry:
539         if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
540                 return -ENOMEM;
541 
542         mutex_lock(&allocated_ptys_lock);
543         if (pty_count >= pty_limit -
544                         (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
545                 mutex_unlock(&allocated_ptys_lock);
546                 return -ENOSPC;
547         }
548 
549         ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
550         if (ida_ret < 0) {
551                 mutex_unlock(&allocated_ptys_lock);
552                 if (ida_ret == -EAGAIN)
553                         goto retry;
554                 return -EIO;
555         }
556 
557         if (index >= fsi->mount_opts.max) {
558                 ida_remove(&fsi->allocated_ptys, index);
559                 mutex_unlock(&allocated_ptys_lock);
560                 return -ENOSPC;
561         }
562         pty_count++;
563         mutex_unlock(&allocated_ptys_lock);
564         return index;
565 }
566 
567 void devpts_kill_index(struct inode *ptmx_inode, int idx)
568 {
569         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
570         struct pts_fs_info *fsi = DEVPTS_SB(sb);
571 
572         mutex_lock(&allocated_ptys_lock);
573         ida_remove(&fsi->allocated_ptys, idx);
574         pty_count--;
575         mutex_unlock(&allocated_ptys_lock);
576 }
577 
578 /**
579  * devpts_pty_new -- create a new inode in /dev/pts/
580  * @ptmx_inode: inode of the master
581  * @device: major+minor of the node to be created
582  * @index: used as a name of the node
583  * @priv: what's given back by devpts_get_priv
584  *
585  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
586  */
587 struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
588                 void *priv)
589 {
590         struct dentry *dentry;
591         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
592         struct inode *inode;
593         struct dentry *root;
594         struct pts_fs_info *fsi;
595         struct pts_mount_opts *opts;
596         char s[12];
597 
598         if (!sb)
599                 return ERR_PTR(-ENODEV);
600 
601         root = sb->s_root;
602         fsi = DEVPTS_SB(sb);
603         opts = &fsi->mount_opts;
604 
605         inode = new_inode(sb);
606         if (!inode)
607                 return ERR_PTR(-ENOMEM);
608 
609         inode->i_ino = index + 3;
610         inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
611         inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
612         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
613         init_special_inode(inode, S_IFCHR|opts->mode, device);
614         inode->i_private = priv;
615 
616         sprintf(s, "%d", index);
617 
618         mutex_lock(&d_inode(root)->i_mutex);
619 
620         dentry = d_alloc_name(root, s);
621         if (dentry) {
622                 d_add(dentry, inode);
623                 fsnotify_create(d_inode(root), dentry);
624         } else {
625                 iput(inode);
626                 inode = ERR_PTR(-ENOMEM);
627         }
628 
629         mutex_unlock(&d_inode(root)->i_mutex);
630 
631         return inode;
632 }
633 
634 /**
635  * devpts_get_priv -- get private data for a slave
636  * @pts_inode: inode of the slave
637  *
638  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
639  */
640 void *devpts_get_priv(struct inode *pts_inode)
641 {
642         struct dentry *dentry;
643         void *priv = NULL;
644 
645         BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
646 
647         /* Ensure dentry has not been deleted by devpts_pty_kill() */
648         dentry = d_find_alias(pts_inode);
649         if (!dentry)
650                 return NULL;
651 
652         if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
653                 priv = pts_inode->i_private;
654 
655         dput(dentry);
656 
657         return priv;
658 }
659 
660 /**
661  * devpts_pty_kill -- remove inode form /dev/pts/
662  * @inode: inode of the slave to be removed
663  *
664  * This is an inverse operation of devpts_pty_new.
665  */
666 void devpts_pty_kill(struct inode *inode)
667 {
668         struct super_block *sb = pts_sb_from_inode(inode);
669         struct dentry *root = sb->s_root;
670         struct dentry *dentry;
671 
672         BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
673 
674         mutex_lock(&d_inode(root)->i_mutex);
675 
676         dentry = d_find_alias(inode);
677 
678         drop_nlink(inode);
679         d_delete(dentry);
680         dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
681         dput(dentry);           /* d_find_alias above */
682 
683         mutex_unlock(&d_inode(root)->i_mutex);
684 }
685 
686 static int __init init_devpts_fs(void)
687 {
688         int err = register_filesystem(&devpts_fs_type);
689         struct ctl_table_header *table;
690 
691         if (!err) {
692                 struct vfsmount *mnt;
693 
694                 table = register_sysctl_table(pty_root_table);
695                 mnt = kern_mount(&devpts_fs_type);
696                 if (IS_ERR(mnt)) {
697                         err = PTR_ERR(mnt);
698                         unregister_filesystem(&devpts_fs_type);
699                         unregister_sysctl_table(table);
700                 } else {
701                         devpts_mnt = mnt;
702                 }
703         }
704         return err;
705 }
706 module_init(init_devpts_fs)
707 

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