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;
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 static DEFINE_MUTEX(allocated_ptys_lock);
98 struct pts_mount_opts {
110 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
114 static const match_table_t tokens = {
117 {Opt_mode, "mode=%o"},
118 {Opt_ptmxmode, "ptmxmode=%o"},
119 {Opt_newinstance, "newinstance"},
125 struct ida allocated_ptys;
126 struct pts_mount_opts mount_opts;
127 struct super_block *sb;
128 struct dentry *ptmx_dentry;
131 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
133 return sb->s_fs_info;
136 static int devpts_ptmx_path(struct path *path)
138 struct super_block *sb;
141 /* Has the devpts filesystem already been found? */
142 if (path->mnt->mnt_sb->s_magic == DEVPTS_SUPER_MAGIC)
145 /* Is a devpts filesystem at "pts" in the same directory? */
146 err = path_pts(path);
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))
159 struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
167 err = devpts_ptmx_path(&path);
171 path.mnt = ERR_PTR(err);
173 if (DEVPTS_SB(path.mnt->mnt_sb) != fsi) {
175 path.mnt = ERR_PTR(-ENODEV);
180 struct pts_fs_info *devpts_acquire(struct file *filp)
182 struct pts_fs_info *result;
184 struct super_block *sb;
190 err = devpts_ptmx_path(&path);
192 result = ERR_PTR(err);
197 * pty code needs to hold extra references in case of last /dev/tty close
199 sb = path.mnt->mnt_sb;
200 atomic_inc(&sb->s_active);
201 result = DEVPTS_SB(sb);
208 void devpts_release(struct pts_fs_info *fsi)
210 deactivate_super(fsi->sb);
213 #define PARSE_MOUNT 0
214 #define PARSE_REMOUNT 1
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.
221 * Note: @data may be NULL (in which case all options are set to default).
223 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
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;
237 /* Only allow instances mounted from the initial mount
238 * namespace to tap the reserve pool of ptys.
240 if (op == PARSE_MOUNT)
242 (current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
244 while ((p = strsep(&data, ",")) != NULL) {
245 substring_t args[MAX_OPT_ARGS];
252 token = match_token(p, tokens, args);
255 if (match_int(&args[0], &option))
257 uid = make_kuid(current_user_ns(), option);
264 if (match_int(&args[0], &option))
266 gid = make_kgid(current_user_ns(), option);
273 if (match_octal(&args[0], &option))
275 opts->mode = option & S_IALLUGO;
278 if (match_octal(&args[0], &option))
280 opts->ptmxmode = option & S_IALLUGO;
282 case Opt_newinstance:
285 if (match_int(&args[0], &option) ||
286 option < 0 || option > NR_UNIX98_PTY_MAX)
291 pr_err("called with bogus options\n");
299 static int mknod_ptmx(struct super_block *sb)
303 struct dentry *dentry;
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();
311 inode_lock(d_inode(root));
313 /* If we have already created ptmx node, return */
314 if (fsi->ptmx_dentry) {
319 dentry = d_alloc_name(root, "ptmx");
321 pr_err("Unable to alloc dentry for ptmx node\n");
326 * Create a new 'ptmx' node in this mount of devpts.
328 inode = new_inode(sb);
330 pr_err("Unable to alloc inode for ptmx node\n");
336 inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
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;
343 d_add(dentry, inode);
345 fsi->ptmx_dentry = dentry;
348 inode_unlock(d_inode(root));
352 static void update_ptmx_mode(struct pts_fs_info *fsi)
355 if (fsi->ptmx_dentry) {
356 inode = d_inode(fsi->ptmx_dentry);
357 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
361 static int devpts_remount(struct super_block *sb, int *flags, char *data)
364 struct pts_fs_info *fsi = DEVPTS_SB(sb);
365 struct pts_mount_opts *opts = &fsi->mount_opts;
367 err = parse_mount_options(data, PARSE_REMOUNT, opts);
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.
375 update_ptmx_mode(fsi);
380 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
382 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
383 struct pts_mount_opts *opts = &fsi->mount_opts;
386 seq_printf(seq, ",uid=%u",
387 from_kuid_munged(&init_user_ns, opts->uid));
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);
399 static const struct super_operations devpts_sops = {
400 .statfs = simple_statfs,
401 .remount_fs = devpts_remount,
402 .show_options = devpts_show_options,
405 static void *new_pts_fs_info(struct super_block *sb)
407 struct pts_fs_info *fsi;
409 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
413 ida_init(&fsi->allocated_ptys);
414 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
415 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
422 devpts_fill_super(struct super_block *s, void *data, int silent)
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;
435 s->s_fs_info = new_pts_fs_info(s);
439 error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
444 inode = new_inode(s);
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;
454 s->s_root = d_make_root(inode);
456 pr_err("get root dentry failed\n");
460 error = mknod_ptmx(s);
475 * Mount a new (private) instance of devpts. PTYs created in this
476 * instance are independent of the PTYs in other devpts instances.
478 static struct dentry *devpts_mount(struct file_system_type *fs_type,
479 int flags, const char *dev_name, void *data)
481 return mount_nodev(fs_type, flags, data, devpts_fill_super);
484 static void devpts_kill_sb(struct super_block *sb)
486 struct pts_fs_info *fsi = DEVPTS_SB(sb);
489 ida_destroy(&fsi->allocated_ptys);
491 kill_litter_super(sb);
494 static struct file_system_type devpts_fs_type = {
496 .mount = devpts_mount,
497 .kill_sb = devpts_kill_sb,
498 .fs_flags = FS_USERNS_MOUNT,
502 * The normal naming convention is simply /dev/pts/<number>; this conforms
503 * to the System V naming convention
506 int devpts_new_index(struct pts_fs_info *fsi)
512 if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
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);
522 ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
524 mutex_unlock(&allocated_ptys_lock);
525 if (ida_ret == -EAGAIN)
530 if (index >= fsi->mount_opts.max) {
531 ida_remove(&fsi->allocated_ptys, index);
532 mutex_unlock(&allocated_ptys_lock);
536 mutex_unlock(&allocated_ptys_lock);
540 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
542 mutex_lock(&allocated_ptys_lock);
543 ida_remove(&fsi->allocated_ptys, idx);
545 mutex_unlock(&allocated_ptys_lock);
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
555 * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
557 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
559 struct dentry *dentry;
560 struct super_block *sb = fsi->sb;
563 struct pts_mount_opts *opts;
567 opts = &fsi->mount_opts;
569 inode = new_inode(sb);
571 return ERR_PTR(-ENOMEM);
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));
579 sprintf(s, "%d", index);
581 dentry = d_alloc_name(root, s);
583 dentry->d_fsdata = priv;
584 d_add(dentry, inode);
585 fsnotify_create(d_inode(root), dentry);
588 dentry = ERR_PTR(-ENOMEM);
595 * devpts_get_priv -- get private data for a slave
596 * @pts_inode: inode of the slave
598 * Returns whatever was passed as priv in devpts_pty_new for a given inode.
600 void *devpts_get_priv(struct dentry *dentry)
602 if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
604 return dentry->d_fsdata;
608 * devpts_pty_kill -- remove inode form /dev/pts/
609 * @inode: inode of the slave to be removed
611 * This is an inverse operation of devpts_pty_new.
613 void devpts_pty_kill(struct dentry *dentry)
615 WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
617 dentry->d_fsdata = NULL;
618 drop_nlink(dentry->d_inode);
620 dput(dentry); /* d_alloc_name() in devpts_pty_new() */
623 static int __init init_devpts_fs(void)
625 int err = register_filesystem(&devpts_fs_type);
627 register_sysctl_table(pty_root_table);
631 module_init(init_devpts_fs)