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TOMOYO Linux Cross Reference
Linux/fs/devpts/inode.c

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  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 atomic_t pty_count = ATOMIC_INIT(0);
 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 struct pts_mount_opts {
 97         int setuid;
 98         int setgid;
 99         kuid_t   uid;
100         kgid_t   gid;
101         umode_t mode;
102         umode_t ptmxmode;
103         int reserve;
104         int max;
105 };
106 
107 enum {
108         Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,  Opt_max,
109         Opt_err
110 };
111 
112 static const match_table_t tokens = {
113         {Opt_uid, "uid=%u"},
114         {Opt_gid, "gid=%u"},
115         {Opt_mode, "mode=%o"},
116         {Opt_ptmxmode, "ptmxmode=%o"},
117         {Opt_newinstance, "newinstance"},
118         {Opt_max, "max=%d"},
119         {Opt_err, NULL}
120 };
121 
122 struct pts_fs_info {
123         struct ida allocated_ptys;
124         struct pts_mount_opts mount_opts;
125         struct super_block *sb;
126         struct dentry *ptmx_dentry;
127 };
128 
129 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
130 {
131         return sb->s_fs_info;
132 }
133 
134 static int devpts_ptmx_path(struct path *path)
135 {
136         struct super_block *sb;
137         int err;
138 
139         /* Is a devpts filesystem at "pts" in the same directory? */
140         err = path_pts(path);
141         if (err)
142                 return err;
143 
144         /* Is the path the root of a devpts filesystem? */
145         sb = path->mnt->mnt_sb;
146         if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
147             (path->mnt->mnt_root != sb->s_root))
148                 return -ENODEV;
149 
150         return 0;
151 }
152 
153 /*
154  * Try to find a suitable devpts filesystem. We support the following
155  * scenarios:
156  * - The ptmx device node is located in the same directory as the devpts
157  *   mount where the pts device nodes are located.
158  *   This is e.g. the case when calling open on the /dev/pts/ptmx device
159  *   node when the devpts filesystem is mounted at /dev/pts.
160  * - The ptmx device node is located outside the devpts filesystem mount
161  *   where the pts device nodes are located. For example, the ptmx device
162  *   is a symlink, separate device node, or bind-mount.
163  *   A supported scenario is bind-mounting /dev/pts/ptmx to /dev/ptmx and
164  *   then calling open on /dev/ptmx. In this case a suitable pts
165  *   subdirectory can be found in the common parent directory /dev of the
166  *   devpts mount and the ptmx bind-mount, after resolving the /dev/ptmx
167  *   bind-mount.
168  *   If no suitable pts subdirectory can be found this function will fail.
169  *   This is e.g. the case when bind-mounting /dev/pts/ptmx to /ptmx.
170  */
171 struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
172 {
173         struct path path;
174         int err = 0;
175 
176         path = filp->f_path;
177         path_get(&path);
178 
179         /* Walk upward while the start point is a bind mount of
180          * a single file.
181          */
182         while (path.mnt->mnt_root == path.dentry)
183                 if (follow_up(&path) == 0)
184                         break;
185 
186         /* devpts_ptmx_path() finds a devpts fs or returns an error. */
187         if ((path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) ||
188             (DEVPTS_SB(path.mnt->mnt_sb) != fsi))
189                 err = devpts_ptmx_path(&path);
190         dput(path.dentry);
191         if (!err) {
192                 if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
193                         return path.mnt;
194 
195                 err = -ENODEV;
196         }
197 
198         mntput(path.mnt);
199         return ERR_PTR(err);
200 }
201 
202 struct pts_fs_info *devpts_acquire(struct file *filp)
203 {
204         struct pts_fs_info *result;
205         struct path path;
206         struct super_block *sb;
207 
208         path = filp->f_path;
209         path_get(&path);
210 
211         /* Has the devpts filesystem already been found? */
212         if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
213                 int err;
214 
215                 err = devpts_ptmx_path(&path);
216                 if (err) {
217                         result = ERR_PTR(err);
218                         goto out;
219                 }
220         }
221 
222         /*
223          * pty code needs to hold extra references in case of last /dev/tty close
224          */
225         sb = path.mnt->mnt_sb;
226         atomic_inc(&sb->s_active);
227         result = DEVPTS_SB(sb);
228 
229 out:
230         path_put(&path);
231         return result;
232 }
233 
234 void devpts_release(struct pts_fs_info *fsi)
235 {
236         deactivate_super(fsi->sb);
237 }
238 
239 #define PARSE_MOUNT     0
240 #define PARSE_REMOUNT   1
241 
242 /*
243  * parse_mount_options():
244  *      Set @opts to mount options specified in @data. If an option is not
245  *      specified in @data, set it to its default value.
246  *
247  * Note: @data may be NULL (in which case all options are set to default).
248  */
249 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
250 {
251         char *p;
252         kuid_t uid;
253         kgid_t gid;
254 
255         opts->setuid  = 0;
256         opts->setgid  = 0;
257         opts->uid     = GLOBAL_ROOT_UID;
258         opts->gid     = GLOBAL_ROOT_GID;
259         opts->mode    = DEVPTS_DEFAULT_MODE;
260         opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
261         opts->max     = NR_UNIX98_PTY_MAX;
262 
263         /* Only allow instances mounted from the initial mount
264          * namespace to tap the reserve pool of ptys.
265          */
266         if (op == PARSE_MOUNT)
267                 opts->reserve =
268                         (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
269 
270         while ((p = strsep(&data, ",")) != NULL) {
271                 substring_t args[MAX_OPT_ARGS];
272                 int token;
273                 int option;
274 
275                 if (!*p)
276                         continue;
277 
278                 token = match_token(p, tokens, args);
279                 switch (token) {
280                 case Opt_uid:
281                         if (match_int(&args[0], &option))
282                                 return -EINVAL;
283                         uid = make_kuid(current_user_ns(), option);
284                         if (!uid_valid(uid))
285                                 return -EINVAL;
286                         opts->uid = uid;
287                         opts->setuid = 1;
288                         break;
289                 case Opt_gid:
290                         if (match_int(&args[0], &option))
291                                 return -EINVAL;
292                         gid = make_kgid(current_user_ns(), option);
293                         if (!gid_valid(gid))
294                                 return -EINVAL;
295                         opts->gid = gid;
296                         opts->setgid = 1;
297                         break;
298                 case Opt_mode:
299                         if (match_octal(&args[0], &option))
300                                 return -EINVAL;
301                         opts->mode = option & S_IALLUGO;
302                         break;
303                 case Opt_ptmxmode:
304                         if (match_octal(&args[0], &option))
305                                 return -EINVAL;
306                         opts->ptmxmode = option & S_IALLUGO;
307                         break;
308                 case Opt_newinstance:
309                         break;
310                 case Opt_max:
311                         if (match_int(&args[0], &option) ||
312                             option < 0 || option > NR_UNIX98_PTY_MAX)
313                                 return -EINVAL;
314                         opts->max = option;
315                         break;
316                 default:
317                         pr_err("called with bogus options\n");
318                         return -EINVAL;
319                 }
320         }
321 
322         return 0;
323 }
324 
325 static int mknod_ptmx(struct super_block *sb)
326 {
327         int mode;
328         int rc = -ENOMEM;
329         struct dentry *dentry;
330         struct inode *inode;
331         struct dentry *root = sb->s_root;
332         struct pts_fs_info *fsi = DEVPTS_SB(sb);
333         struct pts_mount_opts *opts = &fsi->mount_opts;
334         kuid_t ptmx_uid = current_fsuid();
335         kgid_t ptmx_gid = current_fsgid();
336 
337         inode_lock(d_inode(root));
338 
339         /* If we have already created ptmx node, return */
340         if (fsi->ptmx_dentry) {
341                 rc = 0;
342                 goto out;
343         }
344 
345         dentry = d_alloc_name(root, "ptmx");
346         if (!dentry) {
347                 pr_err("Unable to alloc dentry for ptmx node\n");
348                 goto out;
349         }
350 
351         /*
352          * Create a new 'ptmx' node in this mount of devpts.
353          */
354         inode = new_inode(sb);
355         if (!inode) {
356                 pr_err("Unable to alloc inode for ptmx node\n");
357                 dput(dentry);
358                 goto out;
359         }
360 
361         inode->i_ino = 2;
362         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
363 
364         mode = S_IFCHR|opts->ptmxmode;
365         init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
366         inode->i_uid = ptmx_uid;
367         inode->i_gid = ptmx_gid;
368 
369         d_add(dentry, inode);
370 
371         fsi->ptmx_dentry = dentry;
372         rc = 0;
373 out:
374         inode_unlock(d_inode(root));
375         return rc;
376 }
377 
378 static void update_ptmx_mode(struct pts_fs_info *fsi)
379 {
380         struct inode *inode;
381         if (fsi->ptmx_dentry) {
382                 inode = d_inode(fsi->ptmx_dentry);
383                 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
384         }
385 }
386 
387 static int devpts_remount(struct super_block *sb, int *flags, char *data)
388 {
389         int err;
390         struct pts_fs_info *fsi = DEVPTS_SB(sb);
391         struct pts_mount_opts *opts = &fsi->mount_opts;
392 
393         err = parse_mount_options(data, PARSE_REMOUNT, opts);
394 
395         /*
396          * parse_mount_options() restores options to default values
397          * before parsing and may have changed ptmxmode. So, update the
398          * mode in the inode too. Bogus options don't fail the remount,
399          * so do this even on error return.
400          */
401         update_ptmx_mode(fsi);
402 
403         return err;
404 }
405 
406 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
407 {
408         struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
409         struct pts_mount_opts *opts = &fsi->mount_opts;
410 
411         if (opts->setuid)
412                 seq_printf(seq, ",uid=%u",
413                            from_kuid_munged(&init_user_ns, opts->uid));
414         if (opts->setgid)
415                 seq_printf(seq, ",gid=%u",
416                            from_kgid_munged(&init_user_ns, opts->gid));
417         seq_printf(seq, ",mode=%03o", opts->mode);
418         seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
419         if (opts->max < NR_UNIX98_PTY_MAX)
420                 seq_printf(seq, ",max=%d", opts->max);
421 
422         return 0;
423 }
424 
425 static const struct super_operations devpts_sops = {
426         .statfs         = simple_statfs,
427         .remount_fs     = devpts_remount,
428         .show_options   = devpts_show_options,
429 };
430 
431 static void *new_pts_fs_info(struct super_block *sb)
432 {
433         struct pts_fs_info *fsi;
434 
435         fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
436         if (!fsi)
437                 return NULL;
438 
439         ida_init(&fsi->allocated_ptys);
440         fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
441         fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
442         fsi->sb = sb;
443 
444         return fsi;
445 }
446 
447 static int
448 devpts_fill_super(struct super_block *s, void *data, int silent)
449 {
450         struct inode *inode;
451         int error;
452 
453         s->s_iflags &= ~SB_I_NODEV;
454         s->s_blocksize = 1024;
455         s->s_blocksize_bits = 10;
456         s->s_magic = DEVPTS_SUPER_MAGIC;
457         s->s_op = &devpts_sops;
458         s->s_d_op = &simple_dentry_operations;
459         s->s_time_gran = 1;
460 
461         error = -ENOMEM;
462         s->s_fs_info = new_pts_fs_info(s);
463         if (!s->s_fs_info)
464                 goto fail;
465 
466         error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
467         if (error)
468                 goto fail;
469 
470         error = -ENOMEM;
471         inode = new_inode(s);
472         if (!inode)
473                 goto fail;
474         inode->i_ino = 1;
475         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
476         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
477         inode->i_op = &simple_dir_inode_operations;
478         inode->i_fop = &simple_dir_operations;
479         set_nlink(inode, 2);
480 
481         s->s_root = d_make_root(inode);
482         if (!s->s_root) {
483                 pr_err("get root dentry failed\n");
484                 goto fail;
485         }
486 
487         error = mknod_ptmx(s);
488         if (error)
489                 goto fail_dput;
490 
491         return 0;
492 fail_dput:
493         dput(s->s_root);
494         s->s_root = NULL;
495 fail:
496         return error;
497 }
498 
499 /*
500  * devpts_mount()
501  *
502  *     Mount a new (private) instance of devpts.  PTYs created in this
503  *     instance are independent of the PTYs in other devpts instances.
504  */
505 static struct dentry *devpts_mount(struct file_system_type *fs_type,
506         int flags, const char *dev_name, void *data)
507 {
508         return mount_nodev(fs_type, flags, data, devpts_fill_super);
509 }
510 
511 static void devpts_kill_sb(struct super_block *sb)
512 {
513         struct pts_fs_info *fsi = DEVPTS_SB(sb);
514 
515         if (fsi)
516                 ida_destroy(&fsi->allocated_ptys);
517         kfree(fsi);
518         kill_litter_super(sb);
519 }
520 
521 static struct file_system_type devpts_fs_type = {
522         .name           = "devpts",
523         .mount          = devpts_mount,
524         .kill_sb        = devpts_kill_sb,
525         .fs_flags       = FS_USERNS_MOUNT,
526 };
527 
528 /*
529  * The normal naming convention is simply /dev/pts/<number>; this conforms
530  * to the System V naming convention
531  */
532 
533 int devpts_new_index(struct pts_fs_info *fsi)
534 {
535         int index = -ENOSPC;
536 
537         if (atomic_inc_return(&pty_count) >= (pty_limit -
538                           (fsi->mount_opts.reserve ? 0 : pty_reserve)))
539                 goto out;
540 
541         index = ida_alloc_max(&fsi->allocated_ptys, fsi->mount_opts.max - 1,
542                         GFP_KERNEL);
543 
544 out:
545         if (index < 0)
546                 atomic_dec(&pty_count);
547         return index;
548 }
549 
550 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
551 {
552         ida_free(&fsi->allocated_ptys, idx);
553         atomic_dec(&pty_count);
554 }
555 
556 /**
557  * devpts_pty_new -- create a new inode in /dev/pts/
558  * @ptmx_inode: inode of the master
559  * @device: major+minor of the node to be created
560  * @index: used as a name of the node
561  * @priv: what's given back by devpts_get_priv
562  *
563  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
564  */
565 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
566 {
567         struct dentry *dentry;
568         struct super_block *sb = fsi->sb;
569         struct inode *inode;
570         struct dentry *root;
571         struct pts_mount_opts *opts;
572         char s[12];
573 
574         root = sb->s_root;
575         opts = &fsi->mount_opts;
576 
577         inode = new_inode(sb);
578         if (!inode)
579                 return ERR_PTR(-ENOMEM);
580 
581         inode->i_ino = index + 3;
582         inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
583         inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
584         inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
585         init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
586 
587         sprintf(s, "%d", index);
588 
589         dentry = d_alloc_name(root, s);
590         if (dentry) {
591                 dentry->d_fsdata = priv;
592                 d_add(dentry, inode);
593                 fsnotify_create(d_inode(root), dentry);
594         } else {
595                 iput(inode);
596                 dentry = ERR_PTR(-ENOMEM);
597         }
598 
599         return dentry;
600 }
601 
602 /**
603  * devpts_get_priv -- get private data for a slave
604  * @pts_inode: inode of the slave
605  *
606  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
607  */
608 void *devpts_get_priv(struct dentry *dentry)
609 {
610         if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
611                 return NULL;
612         return dentry->d_fsdata;
613 }
614 
615 /**
616  * devpts_pty_kill -- remove inode form /dev/pts/
617  * @inode: inode of the slave to be removed
618  *
619  * This is an inverse operation of devpts_pty_new.
620  */
621 void devpts_pty_kill(struct dentry *dentry)
622 {
623         WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
624 
625         dentry->d_fsdata = NULL;
626         drop_nlink(dentry->d_inode);
627         d_delete(dentry);
628         dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
629 }
630 
631 static int __init init_devpts_fs(void)
632 {
633         int err = register_filesystem(&devpts_fs_type);
634         if (!err) {
635                 register_sysctl_table(pty_root_table);
636         }
637         return err;
638 }
639 module_init(init_devpts_fs)
640 

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