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 #include <linux/module.h>
14 #include <linux/init.h>
15 #include <linux/fs.h>
16 #include <linux/sched.h>
17 #include <linux/namei.h>
18 #include <linux/mount.h>
19 #include <linux/tty.h>
20 #include <linux/mutex.h>
21 #include <linux/idr.h>
22 #include <linux/devpts_fs.h>
23 #include <linux/parser.h>
24 #include <linux/fsnotify.h>
25 #include <linux/seq_file.h>
26
27 #define DEVPTS_SUPER_MAGIC 0x1cd1
28
29 #define DEVPTS_DEFAULT_MODE 0600
30 /*
31 * ptmx is a new node in /dev/pts and will be unused in legacy (single-
32 * instance) mode. To prevent surprises in user space, set permissions of
33 * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
34 * permissions.
35 */
36 #define DEVPTS_DEFAULT_PTMX_MODE 0000
37 #define PTMX_MINOR 2
38
39 extern int pty_limit; /* Config limit on Unix98 ptys */
40 static DEFINE_MUTEX(allocated_ptys_lock);
41
42 static struct vfsmount *devpts_mnt;
43
44 struct pts_mount_opts {
45 int setuid;
46 int setgid;
47 uid_t uid;
48 gid_t gid;
49 umode_t mode;
50 umode_t ptmxmode;
51 int newinstance;
52 };
53
54 enum {
55 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,
56 Opt_err
57 };
58
59 static const match_table_t tokens = {
60 {Opt_uid, "uid=%u"},
61 {Opt_gid, "gid=%u"},
62 {Opt_mode, "mode=%o"},
63 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
64 {Opt_ptmxmode, "ptmxmode=%o"},
65 {Opt_newinstance, "newinstance"},
66 #endif
67 {Opt_err, NULL}
68 };
69
70 struct pts_fs_info {
71 struct ida allocated_ptys;
72 struct pts_mount_opts mount_opts;
73 struct dentry *ptmx_dentry;
74 };
75
76 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
77 {
78 return sb->s_fs_info;
79 }
80
81 static inline struct super_block *pts_sb_from_inode(struct inode *inode)
82 {
83 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
84 if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
85 return inode->i_sb;
86 #endif
87 return devpts_mnt->mnt_sb;
88 }
89
90 #define PARSE_MOUNT 0
91 #define PARSE_REMOUNT 1
92
93 /*
94 * parse_mount_options():
95 * Set @opts to mount options specified in @data. If an option is not
96 * specified in @data, set it to its default value. The exception is
97 * 'newinstance' option which can only be set/cleared on a mount (i.e.
98 * cannot be changed during remount).
99 *
100 * Note: @data may be NULL (in which case all options are set to default).
101 */
102 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
103 {
104 char *p;
105
106 opts->setuid = 0;
107 opts->setgid = 0;
108 opts->uid = 0;
109 opts->gid = 0;
110 opts->mode = DEVPTS_DEFAULT_MODE;
111 opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
112
113 /* newinstance makes sense only on initial mount */
114 if (op == PARSE_MOUNT)
115 opts->newinstance = 0;
116
117 while ((p = strsep(&data, ",")) != NULL) {
118 substring_t args[MAX_OPT_ARGS];
119 int token;
120 int option;
121
122 if (!*p)
123 continue;
124
125 token = match_token(p, tokens, args);
126 switch (token) {
127 case Opt_uid:
128 if (match_int(&args[0], &option))
129 return -EINVAL;
130 opts->uid = option;
131 opts->setuid = 1;
132 break;
133 case Opt_gid:
134 if (match_int(&args[0], &option))
135 return -EINVAL;
136 opts->gid = option;
137 opts->setgid = 1;
138 break;
139 case Opt_mode:
140 if (match_octal(&args[0], &option))
141 return -EINVAL;
142 opts->mode = option & S_IALLUGO;
143 break;
144 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
145 case Opt_ptmxmode:
146 if (match_octal(&args[0], &option))
147 return -EINVAL;
148 opts->ptmxmode = option & S_IALLUGO;
149 break;
150 case Opt_newinstance:
151 /* newinstance makes sense only on initial mount */
152 if (op == PARSE_MOUNT)
153 opts->newinstance = 1;
154 break;
155 #endif
156 default:
157 printk(KERN_ERR "devpts: called with bogus options\n");
158 return -EINVAL;
159 }
160 }
161
162 return 0;
163 }
164
165 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
166 static int mknod_ptmx(struct super_block *sb)
167 {
168 int mode;
169 int rc = -ENOMEM;
170 struct dentry *dentry;
171 struct inode *inode;
172 struct dentry *root = sb->s_root;
173 struct pts_fs_info *fsi = DEVPTS_SB(sb);
174 struct pts_mount_opts *opts = &fsi->mount_opts;
175
176 mutex_lock(&root->d_inode->i_mutex);
177
178 /* If we have already created ptmx node, return */
179 if (fsi->ptmx_dentry) {
180 rc = 0;
181 goto out;
182 }
183
184 dentry = d_alloc_name(root, "ptmx");
185 if (!dentry) {
186 printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
187 goto out;
188 }
189
190 /*
191 * Create a new 'ptmx' node in this mount of devpts.
192 */
193 inode = new_inode(sb);
194 if (!inode) {
195 printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
196 dput(dentry);
197 goto out;
198 }
199
200 inode->i_ino = 2;
201 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
202
203 mode = S_IFCHR|opts->ptmxmode;
204 init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
205
206 d_add(dentry, inode);
207
208 fsi->ptmx_dentry = dentry;
209 rc = 0;
210 out:
211 mutex_unlock(&root->d_inode->i_mutex);
212 return rc;
213 }
214
215 static void update_ptmx_mode(struct pts_fs_info *fsi)
216 {
217 struct inode *inode;
218 if (fsi->ptmx_dentry) {
219 inode = fsi->ptmx_dentry->d_inode;
220 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
221 }
222 }
223 #else
224 static inline void update_ptmx_mode(struct pts_fs_info *fsi)
225 {
226 return;
227 }
228 #endif
229
230 static int devpts_remount(struct super_block *sb, int *flags, char *data)
231 {
232 int err;
233 struct pts_fs_info *fsi = DEVPTS_SB(sb);
234 struct pts_mount_opts *opts = &fsi->mount_opts;
235
236 err = parse_mount_options(data, PARSE_REMOUNT, opts);
237
238 /*
239 * parse_mount_options() restores options to default values
240 * before parsing and may have changed ptmxmode. So, update the
241 * mode in the inode too. Bogus options don't fail the remount,
242 * so do this even on error return.
243 */
244 update_ptmx_mode(fsi);
245
246 return err;
247 }
248
249 static int devpts_show_options(struct seq_file *seq, struct vfsmount *vfs)
250 {
251 struct pts_fs_info *fsi = DEVPTS_SB(vfs->mnt_sb);
252 struct pts_mount_opts *opts = &fsi->mount_opts;
253
254 if (opts->setuid)
255 seq_printf(seq, ",uid=%u", opts->uid);
256 if (opts->setgid)
257 seq_printf(seq, ",gid=%u", opts->gid);
258 seq_printf(seq, ",mode=%03o", opts->mode);
259 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
260 seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
261 #endif
262
263 return 0;
264 }
265
266 static const struct super_operations devpts_sops = {
267 .statfs = simple_statfs,
268 .remount_fs = devpts_remount,
269 .show_options = devpts_show_options,
270 };
271
272 static void *new_pts_fs_info(void)
273 {
274 struct pts_fs_info *fsi;
275
276 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
277 if (!fsi)
278 return NULL;
279
280 ida_init(&fsi->allocated_ptys);
281 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
282 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
283
284 return fsi;
285 }
286
287 static int
288 devpts_fill_super(struct super_block *s, void *data, int silent)
289 {
290 struct inode *inode;
291
292 s->s_blocksize = 1024;
293 s->s_blocksize_bits = 10;
294 s->s_magic = DEVPTS_SUPER_MAGIC;
295 s->s_op = &devpts_sops;
296 s->s_time_gran = 1;
297
298 s->s_fs_info = new_pts_fs_info();
299 if (!s->s_fs_info)
300 goto fail;
301
302 inode = new_inode(s);
303 if (!inode)
304 goto free_fsi;
305 inode->i_ino = 1;
306 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
307 inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
308 inode->i_op = &simple_dir_inode_operations;
309 inode->i_fop = &simple_dir_operations;
310 inode->i_nlink = 2;
311
312 s->s_root = d_alloc_root(inode);
313 if (s->s_root)
314 return 0;
315
316 printk(KERN_ERR "devpts: get root dentry failed\n");
317 iput(inode);
318
319 free_fsi:
320 kfree(s->s_fs_info);
321 fail:
322 return -ENOMEM;
323 }
324
325 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
326 static int compare_init_pts_sb(struct super_block *s, void *p)
327 {
328 if (devpts_mnt)
329 return devpts_mnt->mnt_sb == s;
330 return 0;
331 }
332
333 /*
334 * devpts_get_sb()
335 *
336 * If the '-o newinstance' mount option was specified, mount a new
337 * (private) instance of devpts. PTYs created in this instance are
338 * independent of the PTYs in other devpts instances.
339 *
340 * If the '-o newinstance' option was not specified, mount/remount the
341 * initial kernel mount of devpts. This type of mount gives the
342 * legacy, single-instance semantics.
343 *
344 * The 'newinstance' option is needed to support multiple namespace
345 * semantics in devpts while preserving backward compatibility of the
346 * current 'single-namespace' semantics. i.e all mounts of devpts
347 * without the 'newinstance' mount option should bind to the initial
348 * kernel mount, like get_sb_single().
349 *
350 * Mounts with 'newinstance' option create a new, private namespace.
351 *
352 * NOTE:
353 *
354 * For single-mount semantics, devpts cannot use get_sb_single(),
355 * because get_sb_single()/sget() find and use the super-block from
356 * the most recent mount of devpts. But that recent mount may be a
357 * 'newinstance' mount and get_sb_single() would pick the newinstance
358 * super-block instead of the initial super-block.
359 */
360 static int devpts_get_sb(struct file_system_type *fs_type,
361 int flags, const char *dev_name, void *data, struct vfsmount *mnt)
362 {
363 int error;
364 struct pts_mount_opts opts;
365 struct super_block *s;
366
367 error = parse_mount_options(data, PARSE_MOUNT, &opts);
368 if (error)
369 return error;
370
371 if (opts.newinstance)
372 s = sget(fs_type, NULL, set_anon_super, NULL);
373 else
374 s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
375
376 if (IS_ERR(s))
377 return PTR_ERR(s);
378
379 if (!s->s_root) {
380 s->s_flags = flags;
381 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
382 if (error)
383 goto out_undo_sget;
384 s->s_flags |= MS_ACTIVE;
385 }
386
387 simple_set_mnt(mnt, s);
388
389 memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
390
391 error = mknod_ptmx(s);
392 if (error)
393 goto out_dput;
394
395 return 0;
396
397 out_dput:
398 dput(s->s_root); /* undo dget() in simple_set_mnt() */
399
400 out_undo_sget:
401 deactivate_locked_super(s);
402 return error;
403 }
404
405 #else
406 /*
407 * This supports only the legacy single-instance semantics (no
408 * multiple-instance semantics)
409 */
410 static int devpts_get_sb(struct file_system_type *fs_type, int flags,
411 const char *dev_name, void *data, struct vfsmount *mnt)
412 {
413 return get_sb_single(fs_type, flags, data, devpts_fill_super, mnt);
414 }
415 #endif
416
417 static void devpts_kill_sb(struct super_block *sb)
418 {
419 struct pts_fs_info *fsi = DEVPTS_SB(sb);
420
421 kfree(fsi);
422 kill_litter_super(sb);
423 }
424
425 static struct file_system_type devpts_fs_type = {
426 .name = "devpts",
427 .get_sb = devpts_get_sb,
428 .kill_sb = devpts_kill_sb,
429 };
430
431 /*
432 * The normal naming convention is simply /dev/pts/<number>; this conforms
433 * to the System V naming convention
434 */
435
436 int devpts_new_index(struct inode *ptmx_inode)
437 {
438 struct super_block *sb = pts_sb_from_inode(ptmx_inode);
439 struct pts_fs_info *fsi = DEVPTS_SB(sb);
440 int index;
441 int ida_ret;
442
443 retry:
444 if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
445 return -ENOMEM;
446
447 mutex_lock(&allocated_ptys_lock);
448 ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
449 if (ida_ret < 0) {
450 mutex_unlock(&allocated_ptys_lock);
451 if (ida_ret == -EAGAIN)
452 goto retry;
453 return -EIO;
454 }
455
456 if (index >= pty_limit) {
457 ida_remove(&fsi->allocated_ptys, index);
458 mutex_unlock(&allocated_ptys_lock);
459 return -EIO;
460 }
461 mutex_unlock(&allocated_ptys_lock);
462 return index;
463 }
464
465 void devpts_kill_index(struct inode *ptmx_inode, int idx)
466 {
467 struct super_block *sb = pts_sb_from_inode(ptmx_inode);
468 struct pts_fs_info *fsi = DEVPTS_SB(sb);
469
470 mutex_lock(&allocated_ptys_lock);
471 ida_remove(&fsi->allocated_ptys, idx);
472 mutex_unlock(&allocated_ptys_lock);
473 }
474
475 int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
476 {
477 /* tty layer puts index from devpts_new_index() in here */
478 int number = tty->index;
479 struct tty_driver *driver = tty->driver;
480 dev_t device = MKDEV(driver->major, driver->minor_start+number);
481 struct dentry *dentry;
482 struct super_block *sb = pts_sb_from_inode(ptmx_inode);
483 struct inode *inode = new_inode(sb);
484 struct dentry *root = sb->s_root;
485 struct pts_fs_info *fsi = DEVPTS_SB(sb);
486 struct pts_mount_opts *opts = &fsi->mount_opts;
487 char s[12];
488
489 /* We're supposed to be given the slave end of a pty */
490 BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
491 BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
492
493 if (!inode)
494 return -ENOMEM;
495
496 inode->i_ino = number + 3;
497 inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
498 inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
499 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
500 init_special_inode(inode, S_IFCHR|opts->mode, device);
501 inode->i_private = tty;
502 tty->driver_data = inode;
503
504 sprintf(s, "%d", number);
505
506 mutex_lock(&root->d_inode->i_mutex);
507
508 dentry = d_alloc_name(root, s);
509 if (!IS_ERR(dentry)) {
510 d_add(dentry, inode);
511 fsnotify_create(root->d_inode, dentry);
512 }
513
514 mutex_unlock(&root->d_inode->i_mutex);
515
516 return 0;
517 }
518
519 struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
520 {
521 struct dentry *dentry;
522 struct tty_struct *tty;
523
524 BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
525
526 /* Ensure dentry has not been deleted by devpts_pty_kill() */
527 dentry = d_find_alias(pts_inode);
528 if (!dentry)
529 return NULL;
530
531 tty = NULL;
532 if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
533 tty = (struct tty_struct *)pts_inode->i_private;
534
535 dput(dentry);
536
537 return tty;
538 }
539
540 void devpts_pty_kill(struct tty_struct *tty)
541 {
542 struct inode *inode = tty->driver_data;
543 struct super_block *sb = pts_sb_from_inode(inode);
544 struct dentry *root = sb->s_root;
545 struct dentry *dentry;
546
547 BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
548
549 mutex_lock(&root->d_inode->i_mutex);
550
551 dentry = d_find_alias(inode);
552 if (IS_ERR(dentry))
553 goto out;
554
555 if (dentry) {
556 inode->i_nlink--;
557 d_delete(dentry);
558 dput(dentry); /* d_alloc_name() in devpts_pty_new() */
559 }
560
561 dput(dentry); /* d_find_alias above */
562 out:
563 mutex_unlock(&root->d_inode->i_mutex);
564 }
565
566 static int __init init_devpts_fs(void)
567 {
568 int err = register_filesystem(&devpts_fs_type);
569 if (!err) {
570 devpts_mnt = kern_mount(&devpts_fs_type);
571 if (IS_ERR(devpts_mnt)) {
572 err = PTR_ERR(devpts_mnt);
573 unregister_filesystem(&devpts_fs_type);
574 }
575 }
576 return err;
577 }
578 module_init(init_devpts_fs)
579
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