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 /* Is a devpts filesystem at "pts" in the same directory? */
142 err
= path_pts(path
);
146 /* Is the path the root of a devpts filesystem? */
147 sb
= path
->mnt
->mnt_sb
;
148 if ((sb
->s_magic
!= DEVPTS_SUPER_MAGIC
) ||
149 (path
->mnt
->mnt_root
!= sb
->s_root
))
156 * Try to find a suitable devpts filesystem. We support the following
158 * - The ptmx device node is located in the same directory as the devpts
159 * mount where the pts device nodes are located.
160 * This is e.g. the case when calling open on the /dev/pts/ptmx device
161 * node when the devpts filesystem is mounted at /dev/pts.
162 * - The ptmx device node is located outside the devpts filesystem mount
163 * where the pts device nodes are located. For example, the ptmx device
164 * is a symlink, separate device node, or bind-mount.
165 * A supported scenario is bind-mounting /dev/pts/ptmx to /dev/ptmx and
166 * then calling open on /dev/ptmx. In this case a suitable pts
167 * subdirectory can be found in the common parent directory /dev of the
168 * devpts mount and the ptmx bind-mount, after resolving the /dev/ptmx
170 * If no suitable pts subdirectory can be found this function will fail.
171 * This is e.g. the case when bind-mounting /dev/pts/ptmx to /ptmx.
173 struct vfsmount
*devpts_mntget(struct file
*filp
, struct pts_fs_info
*fsi
)
181 /* Walk upward while the start point is a bind mount of
184 while (path
.mnt
->mnt_root
== path
.dentry
)
185 if (follow_up(&path
) == 0)
188 /* devpts_ptmx_path() finds a devpts fs or returns an error. */
189 if ((path
.mnt
->mnt_sb
->s_magic
!= DEVPTS_SUPER_MAGIC
) ||
190 (DEVPTS_SB(path
.mnt
->mnt_sb
) != fsi
))
191 err
= devpts_ptmx_path(&path
);
194 if (DEVPTS_SB(path
.mnt
->mnt_sb
) == fsi
)
204 struct pts_fs_info
*devpts_acquire(struct file
*filp
)
206 struct pts_fs_info
*result
;
208 struct super_block
*sb
;
213 /* Has the devpts filesystem already been found? */
214 if (path
.mnt
->mnt_sb
->s_magic
!= DEVPTS_SUPER_MAGIC
) {
217 err
= devpts_ptmx_path(&path
);
219 result
= ERR_PTR(err
);
225 * pty code needs to hold extra references in case of last /dev/tty close
227 sb
= path
.mnt
->mnt_sb
;
228 atomic_inc(&sb
->s_active
);
229 result
= DEVPTS_SB(sb
);
236 void devpts_release(struct pts_fs_info
*fsi
)
238 deactivate_super(fsi
->sb
);
241 #define PARSE_MOUNT 0
242 #define PARSE_REMOUNT 1
245 * parse_mount_options():
246 * Set @opts to mount options specified in @data. If an option is not
247 * specified in @data, set it to its default value.
249 * Note: @data may be NULL (in which case all options are set to default).
251 static int parse_mount_options(char *data
, int op
, struct pts_mount_opts
*opts
)
259 opts
->uid
= GLOBAL_ROOT_UID
;
260 opts
->gid
= GLOBAL_ROOT_GID
;
261 opts
->mode
= DEVPTS_DEFAULT_MODE
;
262 opts
->ptmxmode
= DEVPTS_DEFAULT_PTMX_MODE
;
263 opts
->max
= NR_UNIX98_PTY_MAX
;
265 /* Only allow instances mounted from the initial mount
266 * namespace to tap the reserve pool of ptys.
268 if (op
== PARSE_MOUNT
)
270 (current
->nsproxy
->mnt_ns
== init_task
.nsproxy
->mnt_ns
);
272 while ((p
= strsep(&data
, ",")) != NULL
) {
273 substring_t args
[MAX_OPT_ARGS
];
280 token
= match_token(p
, tokens
, args
);
283 if (match_int(&args
[0], &option
))
285 uid
= make_kuid(current_user_ns(), option
);
292 if (match_int(&args
[0], &option
))
294 gid
= make_kgid(current_user_ns(), option
);
301 if (match_octal(&args
[0], &option
))
303 opts
->mode
= option
& S_IALLUGO
;
306 if (match_octal(&args
[0], &option
))
308 opts
->ptmxmode
= option
& S_IALLUGO
;
310 case Opt_newinstance
:
313 if (match_int(&args
[0], &option
) ||
314 option
< 0 || option
> NR_UNIX98_PTY_MAX
)
319 pr_err("called with bogus options\n");
327 static int mknod_ptmx(struct super_block
*sb
)
331 struct dentry
*dentry
;
333 struct dentry
*root
= sb
->s_root
;
334 struct pts_fs_info
*fsi
= DEVPTS_SB(sb
);
335 struct pts_mount_opts
*opts
= &fsi
->mount_opts
;
336 kuid_t ptmx_uid
= current_fsuid();
337 kgid_t ptmx_gid
= current_fsgid();
339 inode_lock(d_inode(root
));
341 /* If we have already created ptmx node, return */
342 if (fsi
->ptmx_dentry
) {
347 dentry
= d_alloc_name(root
, "ptmx");
349 pr_err("Unable to alloc dentry for ptmx node\n");
354 * Create a new 'ptmx' node in this mount of devpts.
356 inode
= new_inode(sb
);
358 pr_err("Unable to alloc inode for ptmx node\n");
364 inode
->i_mtime
= inode
->i_atime
= inode
->i_ctime
= current_time(inode
);
366 mode
= S_IFCHR
|opts
->ptmxmode
;
367 init_special_inode(inode
, mode
, MKDEV(TTYAUX_MAJOR
, 2));
368 inode
->i_uid
= ptmx_uid
;
369 inode
->i_gid
= ptmx_gid
;
371 d_add(dentry
, inode
);
373 fsi
->ptmx_dentry
= dentry
;
376 inode_unlock(d_inode(root
));
380 static void update_ptmx_mode(struct pts_fs_info
*fsi
)
383 if (fsi
->ptmx_dentry
) {
384 inode
= d_inode(fsi
->ptmx_dentry
);
385 inode
->i_mode
= S_IFCHR
|fsi
->mount_opts
.ptmxmode
;
389 static int devpts_remount(struct super_block
*sb
, int *flags
, char *data
)
392 struct pts_fs_info
*fsi
= DEVPTS_SB(sb
);
393 struct pts_mount_opts
*opts
= &fsi
->mount_opts
;
395 err
= parse_mount_options(data
, PARSE_REMOUNT
, opts
);
398 * parse_mount_options() restores options to default values
399 * before parsing and may have changed ptmxmode. So, update the
400 * mode in the inode too. Bogus options don't fail the remount,
401 * so do this even on error return.
403 update_ptmx_mode(fsi
);
408 static int devpts_show_options(struct seq_file
*seq
, struct dentry
*root
)
410 struct pts_fs_info
*fsi
= DEVPTS_SB(root
->d_sb
);
411 struct pts_mount_opts
*opts
= &fsi
->mount_opts
;
414 seq_printf(seq
, ",uid=%u",
415 from_kuid_munged(&init_user_ns
, opts
->uid
));
417 seq_printf(seq
, ",gid=%u",
418 from_kgid_munged(&init_user_ns
, opts
->gid
));
419 seq_printf(seq
, ",mode=%03o", opts
->mode
);
420 seq_printf(seq
, ",ptmxmode=%03o", opts
->ptmxmode
);
421 if (opts
->max
< NR_UNIX98_PTY_MAX
)
422 seq_printf(seq
, ",max=%d", opts
->max
);
427 static const struct super_operations devpts_sops
= {
428 .statfs
= simple_statfs
,
429 .remount_fs
= devpts_remount
,
430 .show_options
= devpts_show_options
,
433 static void *new_pts_fs_info(struct super_block
*sb
)
435 struct pts_fs_info
*fsi
;
437 fsi
= kzalloc(sizeof(struct pts_fs_info
), GFP_KERNEL
);
441 ida_init(&fsi
->allocated_ptys
);
442 fsi
->mount_opts
.mode
= DEVPTS_DEFAULT_MODE
;
443 fsi
->mount_opts
.ptmxmode
= DEVPTS_DEFAULT_PTMX_MODE
;
450 devpts_fill_super(struct super_block
*s
, void *data
, int silent
)
455 s
->s_iflags
&= ~SB_I_NODEV
;
456 s
->s_blocksize
= 1024;
457 s
->s_blocksize_bits
= 10;
458 s
->s_magic
= DEVPTS_SUPER_MAGIC
;
459 s
->s_op
= &devpts_sops
;
460 s
->s_d_op
= &simple_dentry_operations
;
464 s
->s_fs_info
= new_pts_fs_info(s
);
468 error
= parse_mount_options(data
, PARSE_MOUNT
, &DEVPTS_SB(s
)->mount_opts
);
473 inode
= new_inode(s
);
477 inode
->i_mtime
= inode
->i_atime
= inode
->i_ctime
= current_time(inode
);
478 inode
->i_mode
= S_IFDIR
| S_IRUGO
| S_IXUGO
| S_IWUSR
;
479 inode
->i_op
= &simple_dir_inode_operations
;
480 inode
->i_fop
= &simple_dir_operations
;
483 s
->s_root
= d_make_root(inode
);
485 pr_err("get root dentry failed\n");
489 error
= mknod_ptmx(s
);
504 * Mount a new (private) instance of devpts. PTYs created in this
505 * instance are independent of the PTYs in other devpts instances.
507 static struct dentry
*devpts_mount(struct file_system_type
*fs_type
,
508 int flags
, const char *dev_name
, void *data
)
510 return mount_nodev(fs_type
, flags
, data
, devpts_fill_super
);
513 static void devpts_kill_sb(struct super_block
*sb
)
515 struct pts_fs_info
*fsi
= DEVPTS_SB(sb
);
518 ida_destroy(&fsi
->allocated_ptys
);
520 kill_litter_super(sb
);
523 static struct file_system_type devpts_fs_type
= {
525 .mount
= devpts_mount
,
526 .kill_sb
= devpts_kill_sb
,
527 .fs_flags
= FS_USERNS_MOUNT
,
531 * The normal naming convention is simply /dev/pts/<number>; this conforms
532 * to the System V naming convention
535 int devpts_new_index(struct pts_fs_info
*fsi
)
541 if (!ida_pre_get(&fsi
->allocated_ptys
, GFP_KERNEL
))
544 mutex_lock(&allocated_ptys_lock
);
545 if (pty_count
>= (pty_limit
-
546 (fsi
->mount_opts
.reserve
? 0 : pty_reserve
))) {
547 mutex_unlock(&allocated_ptys_lock
);
551 ida_ret
= ida_get_new(&fsi
->allocated_ptys
, &index
);
553 mutex_unlock(&allocated_ptys_lock
);
554 if (ida_ret
== -EAGAIN
)
559 if (index
>= fsi
->mount_opts
.max
) {
560 ida_remove(&fsi
->allocated_ptys
, index
);
561 mutex_unlock(&allocated_ptys_lock
);
565 mutex_unlock(&allocated_ptys_lock
);
569 void devpts_kill_index(struct pts_fs_info
*fsi
, int idx
)
571 mutex_lock(&allocated_ptys_lock
);
572 ida_remove(&fsi
->allocated_ptys
, idx
);
574 mutex_unlock(&allocated_ptys_lock
);
578 * devpts_pty_new -- create a new inode in /dev/pts/
579 * @ptmx_inode: inode of the master
580 * @device: major+minor of the node to be created
581 * @index: used as a name of the node
582 * @priv: what's given back by devpts_get_priv
584 * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
586 struct dentry
*devpts_pty_new(struct pts_fs_info
*fsi
, int index
, void *priv
)
588 struct dentry
*dentry
;
589 struct super_block
*sb
= fsi
->sb
;
592 struct pts_mount_opts
*opts
;
596 opts
= &fsi
->mount_opts
;
598 inode
= new_inode(sb
);
600 return ERR_PTR(-ENOMEM
);
602 inode
->i_ino
= index
+ 3;
603 inode
->i_uid
= opts
->setuid
? opts
->uid
: current_fsuid();
604 inode
->i_gid
= opts
->setgid
? opts
->gid
: current_fsgid();
605 inode
->i_mtime
= inode
->i_atime
= inode
->i_ctime
= current_time(inode
);
606 init_special_inode(inode
, S_IFCHR
|opts
->mode
, MKDEV(UNIX98_PTY_SLAVE_MAJOR
, index
));
608 sprintf(s
, "%d", index
);
610 dentry
= d_alloc_name(root
, s
);
612 dentry
->d_fsdata
= priv
;
613 d_add(dentry
, inode
);
614 fsnotify_create(d_inode(root
), dentry
);
617 dentry
= ERR_PTR(-ENOMEM
);
624 * devpts_get_priv -- get private data for a slave
625 * @pts_inode: inode of the slave
627 * Returns whatever was passed as priv in devpts_pty_new for a given inode.
629 void *devpts_get_priv(struct dentry
*dentry
)
631 if (dentry
->d_sb
->s_magic
!= DEVPTS_SUPER_MAGIC
)
633 return dentry
->d_fsdata
;
637 * devpts_pty_kill -- remove inode form /dev/pts/
638 * @inode: inode of the slave to be removed
640 * This is an inverse operation of devpts_pty_new.
642 void devpts_pty_kill(struct dentry
*dentry
)
644 WARN_ON_ONCE(dentry
->d_sb
->s_magic
!= DEVPTS_SUPER_MAGIC
);
646 dentry
->d_fsdata
= NULL
;
647 drop_nlink(dentry
->d_inode
);
649 dput(dentry
); /* d_alloc_name() in devpts_pty_new() */
652 static int __init
init_devpts_fs(void)
654 int err
= register_filesystem(&devpts_fs_type
);
656 register_sysctl_table(pty_root_table
);
660 module_init(init_devpts_fs
)