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

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