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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 super_block *sb;
132         struct dentry *ptmx_dentry;
133 };
134 
135 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
136 {
137         return sb->s_fs_info;
138 }
139 
140 static inline struct super_block *pts_sb_from_inode(struct inode *inode)
141 {
142 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
143         if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
144                 return inode->i_sb;
145 #endif
146         if (!devpts_mnt)
147                 return NULL;
148         return devpts_mnt->mnt_sb;
149 }
150 
151 #define PARSE_MOUNT     0
152 #define PARSE_REMOUNT   1
153 
154 /*
155  * parse_mount_options():
156  *      Set @opts to mount options specified in @data. If an option is not
157  *      specified in @data, set it to its default value. The exception is
158  *      'newinstance' option which can only be set/cleared on a mount (i.e.
159  *      cannot be changed during remount).
160  *
161  * Note: @data may be NULL (in which case all options are set to default).
162  */
163 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
164 {
165         char *p;
166         kuid_t uid;
167         kgid_t gid;
168 
169         opts->setuid  = 0;
170         opts->setgid  = 0;
171         opts->uid     = GLOBAL_ROOT_UID;
172         opts->gid     = GLOBAL_ROOT_GID;
173         opts->mode    = DEVPTS_DEFAULT_MODE;
174         opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
175         opts->max     = NR_UNIX98_PTY_MAX;
176 
177         /* newinstance makes sense only on initial mount */
178         if (op == PARSE_MOUNT)
179                 opts->newinstance = 0;
180 
181         while ((p = strsep(&data, ",")) != NULL) {
182                 substring_t args[MAX_OPT_ARGS];
183                 int token;
184                 int option;
185 
186                 if (!*p)
187                         continue;
188 
189                 token = match_token(p, tokens, args);
190                 switch (token) {
191                 case Opt_uid:
192                         if (match_int(&args[0], &option))
193                                 return -EINVAL;
194                         uid = make_kuid(current_user_ns(), option);
195                         if (!uid_valid(uid))
196                                 return -EINVAL;
197                         opts->uid = uid;
198                         opts->setuid = 1;
199                         break;
200                 case Opt_gid:
201                         if (match_int(&args[0], &option))
202                                 return -EINVAL;
203                         gid = make_kgid(current_user_ns(), option);
204                         if (!gid_valid(gid))
205                                 return -EINVAL;
206                         opts->gid = gid;
207                         opts->setgid = 1;
208                         break;
209                 case Opt_mode:
210                         if (match_octal(&args[0], &option))
211                                 return -EINVAL;
212                         opts->mode = option & S_IALLUGO;
213                         break;
214 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
215                 case Opt_ptmxmode:
216                         if (match_octal(&args[0], &option))
217                                 return -EINVAL;
218                         opts->ptmxmode = option & S_IALLUGO;
219                         break;
220                 case Opt_newinstance:
221                         /* newinstance makes sense only on initial mount */
222                         if (op == PARSE_MOUNT)
223                                 opts->newinstance = 1;
224                         break;
225                 case Opt_max:
226                         if (match_int(&args[0], &option) ||
227                             option < 0 || option > NR_UNIX98_PTY_MAX)
228                                 return -EINVAL;
229                         opts->max = option;
230                         break;
231 #endif
232                 default:
233                         pr_err("called with bogus options\n");
234                         return -EINVAL;
235                 }
236         }
237 
238         return 0;
239 }
240 
241 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
242 static int mknod_ptmx(struct super_block *sb)
243 {
244         int mode;
245         int rc = -ENOMEM;
246         struct dentry *dentry;
247         struct inode *inode;
248         struct dentry *root = sb->s_root;
249         struct pts_fs_info *fsi = DEVPTS_SB(sb);
250         struct pts_mount_opts *opts = &fsi->mount_opts;
251         kuid_t root_uid;
252         kgid_t root_gid;
253 
254         root_uid = make_kuid(current_user_ns(), 0);
255         root_gid = make_kgid(current_user_ns(), 0);
256         if (!uid_valid(root_uid) || !gid_valid(root_gid))
257                 return -EINVAL;
258 
259         inode_lock(d_inode(root));
260 
261         /* If we have already created ptmx node, return */
262         if (fsi->ptmx_dentry) {
263                 rc = 0;
264                 goto out;
265         }
266 
267         dentry = d_alloc_name(root, "ptmx");
268         if (!dentry) {
269                 pr_err("Unable to alloc dentry for ptmx node\n");
270                 goto out;
271         }
272 
273         /*
274          * Create a new 'ptmx' node in this mount of devpts.
275          */
276         inode = new_inode(sb);
277         if (!inode) {
278                 pr_err("Unable to alloc inode for ptmx node\n");
279                 dput(dentry);
280                 goto out;
281         }
282 
283         inode->i_ino = 2;
284         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
285 
286         mode = S_IFCHR|opts->ptmxmode;
287         init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
288         inode->i_uid = root_uid;
289         inode->i_gid = root_gid;
290 
291         d_add(dentry, inode);
292 
293         fsi->ptmx_dentry = dentry;
294         rc = 0;
295 out:
296         inode_unlock(d_inode(root));
297         return rc;
298 }
299 
300 static void update_ptmx_mode(struct pts_fs_info *fsi)
301 {
302         struct inode *inode;
303         if (fsi->ptmx_dentry) {
304                 inode = d_inode(fsi->ptmx_dentry);
305                 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
306         }
307 }
308 #else
309 static inline void update_ptmx_mode(struct pts_fs_info *fsi)
310 {
311         return;
312 }
313 #endif
314 
315 static int devpts_remount(struct super_block *sb, int *flags, char *data)
316 {
317         int err;
318         struct pts_fs_info *fsi = DEVPTS_SB(sb);
319         struct pts_mount_opts *opts = &fsi->mount_opts;
320 
321         sync_filesystem(sb);
322         err = parse_mount_options(data, PARSE_REMOUNT, opts);
323 
324         /*
325          * parse_mount_options() restores options to default values
326          * before parsing and may have changed ptmxmode. So, update the
327          * mode in the inode too. Bogus options don't fail the remount,
328          * so do this even on error return.
329          */
330         update_ptmx_mode(fsi);
331 
332         return err;
333 }
334 
335 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
336 {
337         struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
338         struct pts_mount_opts *opts = &fsi->mount_opts;
339 
340         if (opts->setuid)
341                 seq_printf(seq, ",uid=%u",
342                            from_kuid_munged(&init_user_ns, opts->uid));
343         if (opts->setgid)
344                 seq_printf(seq, ",gid=%u",
345                            from_kgid_munged(&init_user_ns, opts->gid));
346         seq_printf(seq, ",mode=%03o", opts->mode);
347 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
348         seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
349         if (opts->max < NR_UNIX98_PTY_MAX)
350                 seq_printf(seq, ",max=%d", opts->max);
351 #endif
352 
353         return 0;
354 }
355 
356 static const struct super_operations devpts_sops = {
357         .statfs         = simple_statfs,
358         .remount_fs     = devpts_remount,
359         .show_options   = devpts_show_options,
360 };
361 
362 static void *new_pts_fs_info(struct super_block *sb)
363 {
364         struct pts_fs_info *fsi;
365 
366         fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
367         if (!fsi)
368                 return NULL;
369 
370         ida_init(&fsi->allocated_ptys);
371         fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
372         fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
373         fsi->sb = sb;
374 
375         return fsi;
376 }
377 
378 static int
379 devpts_fill_super(struct super_block *s, void *data, int silent)
380 {
381         struct inode *inode;
382 
383         s->s_blocksize = 1024;
384         s->s_blocksize_bits = 10;
385         s->s_magic = DEVPTS_SUPER_MAGIC;
386         s->s_op = &devpts_sops;
387         s->s_time_gran = 1;
388 
389         s->s_fs_info = new_pts_fs_info(s);
390         if (!s->s_fs_info)
391                 goto fail;
392 
393         inode = new_inode(s);
394         if (!inode)
395                 goto fail;
396         inode->i_ino = 1;
397         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
398         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
399         inode->i_op = &simple_dir_inode_operations;
400         inode->i_fop = &simple_dir_operations;
401         set_nlink(inode, 2);
402 
403         s->s_root = d_make_root(inode);
404         if (s->s_root)
405                 return 0;
406 
407         pr_err("get root dentry failed\n");
408 
409 fail:
410         return -ENOMEM;
411 }
412 
413 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
414 static int compare_init_pts_sb(struct super_block *s, void *p)
415 {
416         if (devpts_mnt)
417                 return devpts_mnt->mnt_sb == s;
418         return 0;
419 }
420 
421 /*
422  * devpts_mount()
423  *
424  *     If the '-o newinstance' mount option was specified, mount a new
425  *     (private) instance of devpts.  PTYs created in this instance are
426  *     independent of the PTYs in other devpts instances.
427  *
428  *     If the '-o newinstance' option was not specified, mount/remount the
429  *     initial kernel mount of devpts.  This type of mount gives the
430  *     legacy, single-instance semantics.
431  *
432  *     The 'newinstance' option is needed to support multiple namespace
433  *     semantics in devpts while preserving backward compatibility of the
434  *     current 'single-namespace' semantics. i.e all mounts of devpts
435  *     without the 'newinstance' mount option should bind to the initial
436  *     kernel mount, like mount_single().
437  *
438  *     Mounts with 'newinstance' option create a new, private namespace.
439  *
440  *     NOTE:
441  *
442  *     For single-mount semantics, devpts cannot use mount_single(),
443  *     because mount_single()/sget() find and use the super-block from
444  *     the most recent mount of devpts. But that recent mount may be a
445  *     'newinstance' mount and mount_single() would pick the newinstance
446  *     super-block instead of the initial super-block.
447  */
448 static struct dentry *devpts_mount(struct file_system_type *fs_type,
449         int flags, const char *dev_name, void *data)
450 {
451         int error;
452         struct pts_mount_opts opts;
453         struct super_block *s;
454 
455         error = parse_mount_options(data, PARSE_MOUNT, &opts);
456         if (error)
457                 return ERR_PTR(error);
458 
459         /* Require newinstance for all user namespace mounts to ensure
460          * the mount options are not changed.
461          */
462         if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
463                 return ERR_PTR(-EINVAL);
464 
465         if (opts.newinstance)
466                 s = sget(fs_type, NULL, set_anon_super, flags, NULL);
467         else
468                 s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
469                          NULL);
470 
471         if (IS_ERR(s))
472                 return ERR_CAST(s);
473 
474         if (!s->s_root) {
475                 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
476                 if (error)
477                         goto out_undo_sget;
478                 s->s_flags |= MS_ACTIVE;
479         }
480 
481         memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
482 
483         error = mknod_ptmx(s);
484         if (error)
485                 goto out_undo_sget;
486 
487         return dget(s->s_root);
488 
489 out_undo_sget:
490         deactivate_locked_super(s);
491         return ERR_PTR(error);
492 }
493 
494 #else
495 /*
496  * This supports only the legacy single-instance semantics (no
497  * multiple-instance semantics)
498  */
499 static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
500                 const char *dev_name, void *data)
501 {
502         return mount_single(fs_type, flags, data, devpts_fill_super);
503 }
504 #endif
505 
506 static void devpts_kill_sb(struct super_block *sb)
507 {
508         struct pts_fs_info *fsi = DEVPTS_SB(sb);
509 
510         ida_destroy(&fsi->allocated_ptys);
511         kfree(fsi);
512         kill_litter_super(sb);
513 }
514 
515 static struct file_system_type devpts_fs_type = {
516         .name           = "devpts",
517         .mount          = devpts_mount,
518         .kill_sb        = devpts_kill_sb,
519 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
520         .fs_flags       = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT,
521 #endif
522 };
523 
524 /*
525  * The normal naming convention is simply /dev/pts/<number>; this conforms
526  * to the System V naming convention
527  */
528 
529 int devpts_new_index(struct pts_fs_info *fsi)
530 {
531         int index;
532         int ida_ret;
533 
534         if (!fsi)
535                 return -ENODEV;
536 
537 retry:
538         if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
539                 return -ENOMEM;
540 
541         mutex_lock(&allocated_ptys_lock);
542         if (pty_count >= pty_limit -
543                         (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
544                 mutex_unlock(&allocated_ptys_lock);
545                 return -ENOSPC;
546         }
547 
548         ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
549         if (ida_ret < 0) {
550                 mutex_unlock(&allocated_ptys_lock);
551                 if (ida_ret == -EAGAIN)
552                         goto retry;
553                 return -EIO;
554         }
555 
556         if (index >= fsi->mount_opts.max) {
557                 ida_remove(&fsi->allocated_ptys, index);
558                 mutex_unlock(&allocated_ptys_lock);
559                 return -ENOSPC;
560         }
561         pty_count++;
562         mutex_unlock(&allocated_ptys_lock);
563         return index;
564 }
565 
566 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
567 {
568         mutex_lock(&allocated_ptys_lock);
569         ida_remove(&fsi->allocated_ptys, idx);
570         pty_count--;
571         mutex_unlock(&allocated_ptys_lock);
572 }
573 
574 /*
575  * pty code needs to hold extra references in case of last /dev/tty close
576  */
577 struct pts_fs_info *devpts_get_ref(struct inode *ptmx_inode, struct file *file)
578 {
579         struct super_block *sb;
580         struct pts_fs_info *fsi;
581 
582         sb = pts_sb_from_inode(ptmx_inode);
583         if (!sb)
584                 return NULL;
585         fsi = DEVPTS_SB(sb);
586         if (!fsi)
587                 return NULL;
588 
589         atomic_inc(&sb->s_active);
590         return fsi;
591 }
592 
593 void devpts_put_ref(struct pts_fs_info *fsi)
594 {
595         deactivate_super(fsi->sb);
596 }
597 
598 /**
599  * devpts_pty_new -- create a new inode in /dev/pts/
600  * @ptmx_inode: inode of the master
601  * @device: major+minor of the node to be created
602  * @index: used as a name of the node
603  * @priv: what's given back by devpts_get_priv
604  *
605  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
606  */
607 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
608 {
609         struct dentry *dentry;
610         struct super_block *sb;
611         struct inode *inode;
612         struct dentry *root;
613         struct pts_mount_opts *opts;
614         char s[12];
615 
616         if (!fsi)
617                 return ERR_PTR(-ENODEV);
618 
619         sb = fsi->sb;
620         root = sb->s_root;
621         opts = &fsi->mount_opts;
622 
623         inode = new_inode(sb);
624         if (!inode)
625                 return ERR_PTR(-ENOMEM);
626 
627         inode->i_ino = index + 3;
628         inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
629         inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
630         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
631         init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
632 
633         sprintf(s, "%d", index);
634 
635         dentry = d_alloc_name(root, s);
636         if (dentry) {
637                 dentry->d_fsdata = priv;
638                 d_add(dentry, inode);
639                 fsnotify_create(d_inode(root), dentry);
640         } else {
641                 iput(inode);
642                 dentry = ERR_PTR(-ENOMEM);
643         }
644 
645         return dentry;
646 }
647 
648 /**
649  * devpts_get_priv -- get private data for a slave
650  * @pts_inode: inode of the slave
651  *
652  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
653  */
654 void *devpts_get_priv(struct dentry *dentry)
655 {
656         WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
657         return dentry->d_fsdata;
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 dentry *dentry)
667 {
668         WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
669 
670         dentry->d_fsdata = NULL;
671         drop_nlink(dentry->d_inode);
672         d_delete(dentry);
673         dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
674 }
675 
676 static int __init init_devpts_fs(void)
677 {
678         int err = register_filesystem(&devpts_fs_type);
679         struct ctl_table_header *table;
680 
681         if (!err) {
682                 struct vfsmount *mnt;
683 
684                 table = register_sysctl_table(pty_root_table);
685                 mnt = kern_mount(&devpts_fs_type);
686                 if (IS_ERR(mnt)) {
687                         err = PTR_ERR(mnt);
688                         unregister_filesystem(&devpts_fs_type);
689                         unregister_sysctl_table(table);
690                 } else {
691                         devpts_mnt = mnt;
692                 }
693         }
694         return err;
695 }
696 module_init(init_devpts_fs)
697 

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