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

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