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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         return devpts_mnt->mnt_sb;
146 }
147 
148 #define PARSE_MOUNT     0
149 #define PARSE_REMOUNT   1
150 
151 /*
152  * parse_mount_options():
153  *      Set @opts to mount options specified in @data. If an option is not
154  *      specified in @data, set it to its default value. The exception is
155  *      'newinstance' option which can only be set/cleared on a mount (i.e.
156  *      cannot be changed during remount).
157  *
158  * Note: @data may be NULL (in which case all options are set to default).
159  */
160 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
161 {
162         char *p;
163         kuid_t uid;
164         kgid_t gid;
165 
166         opts->setuid  = 0;
167         opts->setgid  = 0;
168         opts->uid     = GLOBAL_ROOT_UID;
169         opts->gid     = GLOBAL_ROOT_GID;
170         opts->mode    = DEVPTS_DEFAULT_MODE;
171         opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
172         opts->max     = NR_UNIX98_PTY_MAX;
173 
174         /* newinstance makes sense only on initial mount */
175         if (op == PARSE_MOUNT)
176                 opts->newinstance = 0;
177 
178         while ((p = strsep(&data, ",")) != NULL) {
179                 substring_t args[MAX_OPT_ARGS];
180                 int token;
181                 int option;
182 
183                 if (!*p)
184                         continue;
185 
186                 token = match_token(p, tokens, args);
187                 switch (token) {
188                 case Opt_uid:
189                         if (match_int(&args[0], &option))
190                                 return -EINVAL;
191                         uid = make_kuid(current_user_ns(), option);
192                         if (!uid_valid(uid))
193                                 return -EINVAL;
194                         opts->uid = uid;
195                         opts->setuid = 1;
196                         break;
197                 case Opt_gid:
198                         if (match_int(&args[0], &option))
199                                 return -EINVAL;
200                         gid = make_kgid(current_user_ns(), option);
201                         if (!gid_valid(gid))
202                                 return -EINVAL;
203                         opts->gid = gid;
204                         opts->setgid = 1;
205                         break;
206                 case Opt_mode:
207                         if (match_octal(&args[0], &option))
208                                 return -EINVAL;
209                         opts->mode = option & S_IALLUGO;
210                         break;
211 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
212                 case Opt_ptmxmode:
213                         if (match_octal(&args[0], &option))
214                                 return -EINVAL;
215                         opts->ptmxmode = option & S_IALLUGO;
216                         break;
217                 case Opt_newinstance:
218                         /* newinstance makes sense only on initial mount */
219                         if (op == PARSE_MOUNT)
220                                 opts->newinstance = 1;
221                         break;
222                 case Opt_max:
223                         if (match_int(&args[0], &option) ||
224                             option < 0 || option > NR_UNIX98_PTY_MAX)
225                                 return -EINVAL;
226                         opts->max = option;
227                         break;
228 #endif
229                 default:
230                         pr_err("called with bogus options\n");
231                         return -EINVAL;
232                 }
233         }
234 
235         return 0;
236 }
237 
238 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
239 static int mknod_ptmx(struct super_block *sb)
240 {
241         int mode;
242         int rc = -ENOMEM;
243         struct dentry *dentry;
244         struct inode *inode;
245         struct dentry *root = sb->s_root;
246         struct pts_fs_info *fsi = DEVPTS_SB(sb);
247         struct pts_mount_opts *opts = &fsi->mount_opts;
248         kuid_t root_uid;
249         kgid_t root_gid;
250 
251         root_uid = make_kuid(current_user_ns(), 0);
252         root_gid = make_kgid(current_user_ns(), 0);
253         if (!uid_valid(root_uid) || !gid_valid(root_gid))
254                 return -EINVAL;
255 
256         mutex_lock(&root->d_inode->i_mutex);
257 
258         /* If we have already created ptmx node, return */
259         if (fsi->ptmx_dentry) {
260                 rc = 0;
261                 goto out;
262         }
263 
264         dentry = d_alloc_name(root, "ptmx");
265         if (!dentry) {
266                 pr_err("Unable to alloc dentry for ptmx node\n");
267                 goto out;
268         }
269 
270         /*
271          * Create a new 'ptmx' node in this mount of devpts.
272          */
273         inode = new_inode(sb);
274         if (!inode) {
275                 pr_err("Unable to alloc inode for ptmx node\n");
276                 dput(dentry);
277                 goto out;
278         }
279 
280         inode->i_ino = 2;
281         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
282 
283         mode = S_IFCHR|opts->ptmxmode;
284         init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
285         inode->i_uid = root_uid;
286         inode->i_gid = root_gid;
287 
288         d_add(dentry, inode);
289 
290         fsi->ptmx_dentry = dentry;
291         rc = 0;
292 out:
293         mutex_unlock(&root->d_inode->i_mutex);
294         return rc;
295 }
296 
297 static void update_ptmx_mode(struct pts_fs_info *fsi)
298 {
299         struct inode *inode;
300         if (fsi->ptmx_dentry) {
301                 inode = fsi->ptmx_dentry->d_inode;
302                 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
303         }
304 }
305 #else
306 static inline void update_ptmx_mode(struct pts_fs_info *fsi)
307 {
308         return;
309 }
310 #endif
311 
312 static int devpts_remount(struct super_block *sb, int *flags, char *data)
313 {
314         int err;
315         struct pts_fs_info *fsi = DEVPTS_SB(sb);
316         struct pts_mount_opts *opts = &fsi->mount_opts;
317 
318         sync_filesystem(sb);
319         err = parse_mount_options(data, PARSE_REMOUNT, opts);
320 
321         /*
322          * parse_mount_options() restores options to default values
323          * before parsing and may have changed ptmxmode. So, update the
324          * mode in the inode too. Bogus options don't fail the remount,
325          * so do this even on error return.
326          */
327         update_ptmx_mode(fsi);
328 
329         return err;
330 }
331 
332 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
333 {
334         struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
335         struct pts_mount_opts *opts = &fsi->mount_opts;
336 
337         if (opts->setuid)
338                 seq_printf(seq, ",uid=%u",
339                            from_kuid_munged(&init_user_ns, opts->uid));
340         if (opts->setgid)
341                 seq_printf(seq, ",gid=%u",
342                            from_kgid_munged(&init_user_ns, opts->gid));
343         seq_printf(seq, ",mode=%03o", opts->mode);
344 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
345         seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
346         if (opts->max < NR_UNIX98_PTY_MAX)
347                 seq_printf(seq, ",max=%d", opts->max);
348 #endif
349 
350         return 0;
351 }
352 
353 static const struct super_operations devpts_sops = {
354         .statfs         = simple_statfs,
355         .remount_fs     = devpts_remount,
356         .show_options   = devpts_show_options,
357 };
358 
359 static void *new_pts_fs_info(void)
360 {
361         struct pts_fs_info *fsi;
362 
363         fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
364         if (!fsi)
365                 return NULL;
366 
367         ida_init(&fsi->allocated_ptys);
368         fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
369         fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
370 
371         return fsi;
372 }
373 
374 static int
375 devpts_fill_super(struct super_block *s, void *data, int silent)
376 {
377         struct inode *inode;
378 
379         s->s_blocksize = 1024;
380         s->s_blocksize_bits = 10;
381         s->s_magic = DEVPTS_SUPER_MAGIC;
382         s->s_op = &devpts_sops;
383         s->s_time_gran = 1;
384 
385         s->s_fs_info = new_pts_fs_info();
386         if (!s->s_fs_info)
387                 goto fail;
388 
389         inode = new_inode(s);
390         if (!inode)
391                 goto fail;
392         inode->i_ino = 1;
393         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
394         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
395         inode->i_op = &simple_dir_inode_operations;
396         inode->i_fop = &simple_dir_operations;
397         set_nlink(inode, 2);
398 
399         s->s_root = d_make_root(inode);
400         if (s->s_root)
401                 return 0;
402 
403         pr_err("get root dentry failed\n");
404 
405 fail:
406         return -ENOMEM;
407 }
408 
409 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
410 static int compare_init_pts_sb(struct super_block *s, void *p)
411 {
412         if (devpts_mnt)
413                 return devpts_mnt->mnt_sb == s;
414         return 0;
415 }
416 
417 /*
418  * devpts_mount()
419  *
420  *     If the '-o newinstance' mount option was specified, mount a new
421  *     (private) instance of devpts.  PTYs created in this instance are
422  *     independent of the PTYs in other devpts instances.
423  *
424  *     If the '-o newinstance' option was not specified, mount/remount the
425  *     initial kernel mount of devpts.  This type of mount gives the
426  *     legacy, single-instance semantics.
427  *
428  *     The 'newinstance' option is needed to support multiple namespace
429  *     semantics in devpts while preserving backward compatibility of the
430  *     current 'single-namespace' semantics. i.e all mounts of devpts
431  *     without the 'newinstance' mount option should bind to the initial
432  *     kernel mount, like mount_single().
433  *
434  *     Mounts with 'newinstance' option create a new, private namespace.
435  *
436  *     NOTE:
437  *
438  *     For single-mount semantics, devpts cannot use mount_single(),
439  *     because mount_single()/sget() find and use the super-block from
440  *     the most recent mount of devpts. But that recent mount may be a
441  *     'newinstance' mount and mount_single() would pick the newinstance
442  *     super-block instead of the initial super-block.
443  */
444 static struct dentry *devpts_mount(struct file_system_type *fs_type,
445         int flags, const char *dev_name, void *data)
446 {
447         int error;
448         struct pts_mount_opts opts;
449         struct super_block *s;
450 
451         error = parse_mount_options(data, PARSE_MOUNT, &opts);
452         if (error)
453                 return ERR_PTR(error);
454 
455         /* Require newinstance for all user namespace mounts to ensure
456          * the mount options are not changed.
457          */
458         if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
459                 return ERR_PTR(-EINVAL);
460 
461         if (opts.newinstance)
462                 s = sget(fs_type, NULL, set_anon_super, flags, NULL);
463         else
464                 s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
465                          NULL);
466 
467         if (IS_ERR(s))
468                 return ERR_CAST(s);
469 
470         if (!s->s_root) {
471                 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
472                 if (error)
473                         goto out_undo_sget;
474                 s->s_flags |= MS_ACTIVE;
475         }
476 
477         memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
478 
479         error = mknod_ptmx(s);
480         if (error)
481                 goto out_undo_sget;
482 
483         return dget(s->s_root);
484 
485 out_undo_sget:
486         deactivate_locked_super(s);
487         return ERR_PTR(error);
488 }
489 
490 #else
491 /*
492  * This supports only the legacy single-instance semantics (no
493  * multiple-instance semantics)
494  */
495 static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
496                 const char *dev_name, void *data)
497 {
498         return mount_single(fs_type, flags, data, devpts_fill_super);
499 }
500 #endif
501 
502 static void devpts_kill_sb(struct super_block *sb)
503 {
504         struct pts_fs_info *fsi = DEVPTS_SB(sb);
505 
506         ida_destroy(&fsi->allocated_ptys);
507         kfree(fsi);
508         kill_litter_super(sb);
509 }
510 
511 static struct file_system_type devpts_fs_type = {
512         .name           = "devpts",
513         .mount          = devpts_mount,
514         .kill_sb        = devpts_kill_sb,
515 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
516         .fs_flags       = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT,
517 #endif
518 };
519 
520 /*
521  * The normal naming convention is simply /dev/pts/<number>; this conforms
522  * to the System V naming convention
523  */
524 
525 int devpts_new_index(struct inode *ptmx_inode)
526 {
527         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
528         struct pts_fs_info *fsi = DEVPTS_SB(sb);
529         int index;
530         int ida_ret;
531 
532 retry:
533         if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
534                 return -ENOMEM;
535 
536         mutex_lock(&allocated_ptys_lock);
537         if (pty_count >= pty_limit -
538                         (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
539                 mutex_unlock(&allocated_ptys_lock);
540                 return -ENOSPC;
541         }
542 
543         ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
544         if (ida_ret < 0) {
545                 mutex_unlock(&allocated_ptys_lock);
546                 if (ida_ret == -EAGAIN)
547                         goto retry;
548                 return -EIO;
549         }
550 
551         if (index >= fsi->mount_opts.max) {
552                 ida_remove(&fsi->allocated_ptys, index);
553                 mutex_unlock(&allocated_ptys_lock);
554                 return -ENOSPC;
555         }
556         pty_count++;
557         mutex_unlock(&allocated_ptys_lock);
558         return index;
559 }
560 
561 void devpts_kill_index(struct inode *ptmx_inode, int idx)
562 {
563         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
564         struct pts_fs_info *fsi = DEVPTS_SB(sb);
565 
566         mutex_lock(&allocated_ptys_lock);
567         ida_remove(&fsi->allocated_ptys, idx);
568         pty_count--;
569         mutex_unlock(&allocated_ptys_lock);
570 }
571 
572 /**
573  * devpts_pty_new -- create a new inode in /dev/pts/
574  * @ptmx_inode: inode of the master
575  * @device: major+minor of the node to be created
576  * @index: used as a name of the node
577  * @priv: what's given back by devpts_get_priv
578  *
579  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
580  */
581 struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
582                 void *priv)
583 {
584         struct dentry *dentry;
585         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
586         struct inode *inode;
587         struct dentry *root = sb->s_root;
588         struct pts_fs_info *fsi = DEVPTS_SB(sb);
589         struct pts_mount_opts *opts = &fsi->mount_opts;
590         char s[12];
591 
592         inode = new_inode(sb);
593         if (!inode)
594                 return ERR_PTR(-ENOMEM);
595 
596         inode->i_ino = index + 3;
597         inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
598         inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
599         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
600         init_special_inode(inode, S_IFCHR|opts->mode, device);
601         inode->i_private = priv;
602 
603         sprintf(s, "%d", index);
604 
605         mutex_lock(&root->d_inode->i_mutex);
606 
607         dentry = d_alloc_name(root, s);
608         if (dentry) {
609                 d_add(dentry, inode);
610                 fsnotify_create(root->d_inode, dentry);
611         } else {
612                 iput(inode);
613                 inode = ERR_PTR(-ENOMEM);
614         }
615 
616         mutex_unlock(&root->d_inode->i_mutex);
617 
618         return inode;
619 }
620 
621 /**
622  * devpts_get_priv -- get private data for a slave
623  * @pts_inode: inode of the slave
624  *
625  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
626  */
627 void *devpts_get_priv(struct inode *pts_inode)
628 {
629         struct dentry *dentry;
630         void *priv = NULL;
631 
632         BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
633 
634         /* Ensure dentry has not been deleted by devpts_pty_kill() */
635         dentry = d_find_alias(pts_inode);
636         if (!dentry)
637                 return NULL;
638 
639         if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
640                 priv = pts_inode->i_private;
641 
642         dput(dentry);
643 
644         return priv;
645 }
646 
647 /**
648  * devpts_pty_kill -- remove inode form /dev/pts/
649  * @inode: inode of the slave to be removed
650  *
651  * This is an inverse operation of devpts_pty_new.
652  */
653 void devpts_pty_kill(struct inode *inode)
654 {
655         struct super_block *sb = pts_sb_from_inode(inode);
656         struct dentry *root = sb->s_root;
657         struct dentry *dentry;
658 
659         BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
660 
661         mutex_lock(&root->d_inode->i_mutex);
662 
663         dentry = d_find_alias(inode);
664 
665         drop_nlink(inode);
666         d_delete(dentry);
667         dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
668         dput(dentry);           /* d_find_alias above */
669 
670         mutex_unlock(&root->d_inode->i_mutex);
671 }
672 
673 static int __init init_devpts_fs(void)
674 {
675         int err = register_filesystem(&devpts_fs_type);
676         struct ctl_table_header *table;
677 
678         if (!err) {
679                 table = register_sysctl_table(pty_root_table);
680                 devpts_mnt = kern_mount(&devpts_fs_type);
681                 if (IS_ERR(devpts_mnt)) {
682                         err = PTR_ERR(devpts_mnt);
683                         unregister_filesystem(&devpts_fs_type);
684                         unregister_sysctl_table(table);
685                 }
686         }
687         return err;
688 }
689 module_init(init_devpts_fs)
690 

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