1 /* -*- linux-c -*- --------------------------------------------------------- *
3 * linux/fs/devpts/inode.c
5 * Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
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.
11 * ------------------------------------------------------------------------- */
13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
15 #include <linux/module.h>
16 #include <linux/init.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>
31 #define DEVPTS_DEFAULT_MODE 0600
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
38 #define DEVPTS_DEFAULT_PTMX_MODE 0000
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.
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);
51 static struct ctl_table pty_table[] = {
54 .maxlen = sizeof(int),
57 .proc_handler = proc_dointvec_minmax,
58 .extra1 = &pty_limit_min,
59 .extra2 = &pty_limit_max,
61 .procname = "reserve",
62 .maxlen = sizeof(int),
65 .proc_handler = proc_dointvec_minmax,
66 .extra1 = &pty_limit_min,
67 .extra2 = &pty_limit_max,
70 .maxlen = sizeof(int),
73 .proc_handler = proc_dointvec,
78 static struct ctl_table pty_kern_table[] = {
87 static struct ctl_table pty_root_table[] = {
91 .child = pty_kern_table,
96 struct pts_mount_opts {
108 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
112 static const match_table_t tokens = {
115 {Opt_mode, "mode=%o"},
116 {Opt_ptmxmode, "ptmxmode=%o"},
117 {Opt_newinstance, "newinstance"},
123 struct ida allocated_ptys;
124 struct pts_mount_opts mount_opts;
125 struct super_block *sb;
126 struct dentry *ptmx_dentry;
129 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
131 return sb->s_fs_info;
134 static int devpts_ptmx_path(struct path *path)
136 struct super_block *sb;
139 /* Is a devpts filesystem at "pts" in the same directory? */
140 err = path_pts(path);
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))
154 * Try to find a suitable devpts filesystem. We support the following
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
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.
171 struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
179 /* Walk upward while the start point is a bind mount of
182 while (path.mnt->mnt_root == path.dentry)
183 if (follow_up(&path) == 0)
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);
192 if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
202 struct pts_fs_info *devpts_acquire(struct file *filp)
204 struct pts_fs_info *result;
206 struct super_block *sb;
211 /* Has the devpts filesystem already been found? */
212 if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
215 err = devpts_ptmx_path(&path);
217 result = ERR_PTR(err);
223 * pty code needs to hold extra references in case of last /dev/tty close
225 sb = path.mnt->mnt_sb;
226 atomic_inc(&sb->s_active);
227 result = DEVPTS_SB(sb);
234 void devpts_release(struct pts_fs_info *fsi)
236 deactivate_super(fsi->sb);
239 #define PARSE_MOUNT 0
240 #define PARSE_REMOUNT 1
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.
247 * Note: @data may be NULL (in which case all options are set to default).
249 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
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;
263 /* Only allow instances mounted from the initial mount
264 * namespace to tap the reserve pool of ptys.
266 if (op == PARSE_MOUNT)
268 (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
270 while ((p = strsep(&data, ",")) != NULL) {
271 substring_t args[MAX_OPT_ARGS];
278 token = match_token(p, tokens, args);
281 if (match_int(&args[0], &option))
283 uid = make_kuid(current_user_ns(), option);
290 if (match_int(&args[0], &option))
292 gid = make_kgid(current_user_ns(), option);
299 if (match_octal(&args[0], &option))
301 opts->mode = option & S_IALLUGO;
304 if (match_octal(&args[0], &option))
306 opts->ptmxmode = option & S_IALLUGO;
308 case Opt_newinstance:
311 if (match_int(&args[0], &option) ||
312 option < 0 || option > NR_UNIX98_PTY_MAX)
317 pr_err("called with bogus options\n");
325 static int mknod_ptmx(struct super_block *sb)
329 struct dentry *dentry;
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();
337 inode_lock(d_inode(root));
339 /* If we have already created ptmx node, return */
340 if (fsi->ptmx_dentry) {
345 dentry = d_alloc_name(root, "ptmx");
347 pr_err("Unable to alloc dentry for ptmx node\n");
352 * Create a new 'ptmx' node in this mount of devpts.
354 inode = new_inode(sb);
356 pr_err("Unable to alloc inode for ptmx node\n");
362 inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
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;
369 d_add(dentry, inode);
371 fsi->ptmx_dentry = dentry;
374 inode_unlock(d_inode(root));
378 static void update_ptmx_mode(struct pts_fs_info *fsi)
381 if (fsi->ptmx_dentry) {
382 inode = d_inode(fsi->ptmx_dentry);
383 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
387 static int devpts_remount(struct super_block *sb, int *flags, char *data)
390 struct pts_fs_info *fsi = DEVPTS_SB(sb);
391 struct pts_mount_opts *opts = &fsi->mount_opts;
393 err = parse_mount_options(data, PARSE_REMOUNT, opts);
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.
401 update_ptmx_mode(fsi);
406 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
408 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
409 struct pts_mount_opts *opts = &fsi->mount_opts;
412 seq_printf(seq, ",uid=%u",
413 from_kuid_munged(&init_user_ns, opts->uid));
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);
425 static const struct super_operations devpts_sops = {
426 .statfs = simple_statfs,
427 .remount_fs = devpts_remount,
428 .show_options = devpts_show_options,
431 static void *new_pts_fs_info(struct super_block *sb)
433 struct pts_fs_info *fsi;
435 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
439 ida_init(&fsi->allocated_ptys);
440 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
441 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
448 devpts_fill_super(struct super_block *s, void *data, int silent)
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;
462 s->s_fs_info = new_pts_fs_info(s);
466 error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
471 inode = new_inode(s);
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;
481 s->s_root = d_make_root(inode);
483 pr_err("get root dentry failed\n");
487 error = mknod_ptmx(s);
502 * Mount a new (private) instance of devpts. PTYs created in this
503 * instance are independent of the PTYs in other devpts instances.
505 static struct dentry *devpts_mount(struct file_system_type *fs_type,
506 int flags, const char *dev_name, void *data)
508 return mount_nodev(fs_type, flags, data, devpts_fill_super);
511 static void devpts_kill_sb(struct super_block *sb)
513 struct pts_fs_info *fsi = DEVPTS_SB(sb);
516 ida_destroy(&fsi->allocated_ptys);
518 kill_litter_super(sb);
521 static struct file_system_type devpts_fs_type = {
523 .mount = devpts_mount,
524 .kill_sb = devpts_kill_sb,
525 .fs_flags = FS_USERNS_MOUNT,
529 * The normal naming convention is simply /dev/pts/<number>; this conforms
530 * to the System V naming convention
533 int devpts_new_index(struct pts_fs_info *fsi)
537 if (atomic_inc_return(&pty_count) >= (pty_limit -
538 (fsi->mount_opts.reserve ? 0 : pty_reserve)))
541 index = ida_alloc_max(&fsi->allocated_ptys, fsi->mount_opts.max - 1,
546 atomic_dec(&pty_count);
550 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
552 ida_free(&fsi->allocated_ptys, idx);
553 atomic_dec(&pty_count);
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
563 * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
565 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
567 struct dentry *dentry;
568 struct super_block *sb = fsi->sb;
571 struct pts_mount_opts *opts;
575 opts = &fsi->mount_opts;
577 inode = new_inode(sb);
579 return ERR_PTR(-ENOMEM);
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));
587 sprintf(s, "%d", index);
589 dentry = d_alloc_name(root, s);
591 dentry->d_fsdata = priv;
592 d_add(dentry, inode);
593 fsnotify_create(d_inode(root), dentry);
596 dentry = ERR_PTR(-ENOMEM);
603 * devpts_get_priv -- get private data for a slave
604 * @pts_inode: inode of the slave
606 * Returns whatever was passed as priv in devpts_pty_new for a given inode.
608 void *devpts_get_priv(struct dentry *dentry)
610 if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
612 return dentry->d_fsdata;
616 * devpts_pty_kill -- remove inode form /dev/pts/
617 * @inode: inode of the slave to be removed
619 * This is an inverse operation of devpts_pty_new.
621 void devpts_pty_kill(struct dentry *dentry)
623 WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
625 dentry->d_fsdata = NULL;
626 drop_nlink(dentry->d_inode);
628 dput(dentry); /* d_alloc_name() in devpts_pty_new() */
631 static int __init init_devpts_fs(void)
633 int err = register_filesystem(&devpts_fs_type);
635 register_sysctl_table(pty_root_table);
639 module_init(init_devpts_fs)