// SPDX-License-Identifier: GPL-2.0-or-later
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/* -*- linux-c -*- --------------------------------------------------------- *
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*
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* linux/fs/devpts/inode.c
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*
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* Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
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*
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* ------------------------------------------------------------------------- */
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/namei.h>
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#include <linux/slab.h>
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#include <linux/mount.h>
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#include <linux/tty.h>
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#include <linux/mutex.h>
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#include <linux/magic.h>
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#include <linux/idr.h>
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#include <linux/devpts_fs.h>
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#include <linux/parser.h>
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#include <linux/fsnotify.h>
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#include <linux/seq_file.h>
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#define DEVPTS_DEFAULT_MODE 0600
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/*
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* ptmx is a new node in /dev/pts and will be unused in legacy (single-
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* instance) mode. To prevent surprises in user space, set permissions of
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* ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
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* permissions.
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*/
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#define DEVPTS_DEFAULT_PTMX_MODE 0000
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#define PTMX_MINOR 2
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/*
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* sysctl support for setting limits on the number of Unix98 ptys allocated.
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* Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
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*/
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static int pty_limit = NR_UNIX98_PTY_DEFAULT;
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static int pty_reserve = NR_UNIX98_PTY_RESERVE;
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static int pty_limit_min;
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static int pty_limit_max = INT_MAX;
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static atomic_t pty_count = ATOMIC_INIT(0);
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static struct ctl_table pty_table[] = {
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{
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.procname = "max",
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.maxlen = sizeof(int),
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.mode = 0644,
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.data = &pty_limit,
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.proc_handler = proc_dointvec_minmax,
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.extra1 = &pty_limit_min,
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.extra2 = &pty_limit_max,
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}, {
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.procname = "reserve",
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.maxlen = sizeof(int),
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.mode = 0644,
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.data = &pty_reserve,
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.proc_handler = proc_dointvec_minmax,
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.extra1 = &pty_limit_min,
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.extra2 = &pty_limit_max,
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}, {
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.procname = "nr",
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.maxlen = sizeof(int),
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.mode = 0444,
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.data = &pty_count,
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.proc_handler = proc_dointvec,
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},
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{}
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};
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static struct ctl_table pty_kern_table[] = {
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{
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.procname = "pty",
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.mode = 0555,
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.child = pty_table,
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},
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{}
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};
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static struct ctl_table pty_root_table[] = {
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{
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.procname = "kernel",
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.mode = 0555,
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.child = pty_kern_table,
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},
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{}
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};
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struct pts_mount_opts {
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int setuid;
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int setgid;
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kuid_t uid;
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kgid_t gid;
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umode_t mode;
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umode_t ptmxmode;
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int reserve;
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int max;
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};
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enum {
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Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
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Opt_err
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};
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static const match_table_t tokens = {
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{Opt_uid, "uid=%u"},
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{Opt_gid, "gid=%u"},
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{Opt_mode, "mode=%o"},
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{Opt_ptmxmode, "ptmxmode=%o"},
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{Opt_newinstance, "newinstance"},
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{Opt_max, "max=%d"},
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{Opt_err, NULL}
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};
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struct pts_fs_info {
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struct ida allocated_ptys;
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struct pts_mount_opts mount_opts;
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struct super_block *sb;
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struct dentry *ptmx_dentry;
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};
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static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
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{
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return sb->s_fs_info;
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}
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static int devpts_ptmx_path(struct path *path)
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{
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struct super_block *sb;
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int err;
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/* Is a devpts filesystem at "pts" in the same directory? */
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err = path_pts(path);
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if (err)
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return err;
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/* Is the path the root of a devpts filesystem? */
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sb = path->mnt->mnt_sb;
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if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
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(path->mnt->mnt_root != sb->s_root))
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return -ENODEV;
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return 0;
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}
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/*
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* Try to find a suitable devpts filesystem. We support the following
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* scenarios:
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* - The ptmx device node is located in the same directory as the devpts
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* mount where the pts device nodes are located.
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* This is e.g. the case when calling open on the /dev/pts/ptmx device
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* node when the devpts filesystem is mounted at /dev/pts.
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* - The ptmx device node is located outside the devpts filesystem mount
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* where the pts device nodes are located. For example, the ptmx device
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* is a symlink, separate device node, or bind-mount.
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* A supported scenario is bind-mounting /dev/pts/ptmx to /dev/ptmx and
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* then calling open on /dev/ptmx. In this case a suitable pts
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* subdirectory can be found in the common parent directory /dev of the
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* devpts mount and the ptmx bind-mount, after resolving the /dev/ptmx
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* bind-mount.
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* If no suitable pts subdirectory can be found this function will fail.
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* This is e.g. the case when bind-mounting /dev/pts/ptmx to /ptmx.
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*/
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struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
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{
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struct path path;
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int err = 0;
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path = filp->f_path;
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path_get(&path);
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/* Walk upward while the start point is a bind mount of
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* a single file.
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*/
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while (path.mnt->mnt_root == path.dentry)
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if (follow_up(&path) == 0)
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break;
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/* devpts_ptmx_path() finds a devpts fs or returns an error. */
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if ((path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) ||
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(DEVPTS_SB(path.mnt->mnt_sb) != fsi))
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err = devpts_ptmx_path(&path);
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dput(path.dentry);
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if (!err) {
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if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
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return path.mnt;
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err = -ENODEV;
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}
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mntput(path.mnt);
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return ERR_PTR(err);
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}
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struct pts_fs_info *devpts_acquire(struct file *filp)
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{
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struct pts_fs_info *result;
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struct path path;
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struct super_block *sb;
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path = filp->f_path;
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path_get(&path);
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/* Has the devpts filesystem already been found? */
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if (path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) {
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int err;
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err = devpts_ptmx_path(&path);
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if (err) {
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result = ERR_PTR(err);
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goto out;
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}
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}
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/*
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* pty code needs to hold extra references in case of last /dev/tty close
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*/
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sb = path.mnt->mnt_sb;
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atomic_inc(&sb->s_active);
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result = DEVPTS_SB(sb);
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out:
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path_put(&path);
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return result;
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}
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void devpts_release(struct pts_fs_info *fsi)
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{
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deactivate_super(fsi->sb);
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}
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#define PARSE_MOUNT 0
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#define PARSE_REMOUNT 1
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/*
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* parse_mount_options():
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* Set @opts to mount options specified in @data. If an option is not
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* specified in @data, set it to its default value.
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*
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* Note: @data may be NULL (in which case all options are set to default).
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*/
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static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
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{
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char *p;
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kuid_t uid;
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kgid_t gid;
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opts->setuid = 0;
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opts->setgid = 0;
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opts->uid = GLOBAL_ROOT_UID;
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opts->gid = GLOBAL_ROOT_GID;
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opts->mode = DEVPTS_DEFAULT_MODE;
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opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
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opts->max = NR_UNIX98_PTY_MAX;
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/* Only allow instances mounted from the initial mount
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* namespace to tap the reserve pool of ptys.
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*/
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if (op == PARSE_MOUNT)
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opts->reserve =
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(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);
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while ((p = strsep(&data, ",")) != NULL) {
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substring_t args[MAX_OPT_ARGS];
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int token;
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int option;
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if (!*p)
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continue;
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token = match_token(p, tokens, args);
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switch (token) {
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case Opt_uid:
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if (match_int(&args[0], &option))
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return -EINVAL;
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uid = make_kuid(current_user_ns(), option);
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if (!uid_valid(uid))
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return -EINVAL;
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opts->uid = uid;
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opts->setuid = 1;
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break;
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case Opt_gid:
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if (match_int(&args[0], &option))
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return -EINVAL;
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gid = make_kgid(current_user_ns(), option);
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if (!gid_valid(gid))
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return -EINVAL;
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opts->gid = gid;
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opts->setgid = 1;
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break;
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case Opt_mode:
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if (match_octal(&args[0], &option))
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return -EINVAL;
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opts->mode = option & S_IALLUGO;
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break;
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case Opt_ptmxmode:
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if (match_octal(&args[0], &option))
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return -EINVAL;
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opts->ptmxmode = option & S_IALLUGO;
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break;
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case Opt_newinstance:
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break;
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case Opt_max:
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if (match_int(&args[0], &option) ||
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option < 0 || option > NR_UNIX98_PTY_MAX)
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return -EINVAL;
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opts->max = option;
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break;
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default:
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pr_err("called with bogus options\n");
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return -EINVAL;
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}
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}
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return 0;
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}
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static int mknod_ptmx(struct super_block *sb)
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{
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int mode;
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int rc = -ENOMEM;
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struct dentry *dentry;
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struct inode *inode;
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struct dentry *root = sb->s_root;
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
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struct pts_mount_opts *opts = &fsi->mount_opts;
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kuid_t ptmx_uid = current_fsuid();
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kgid_t ptmx_gid = current_fsgid();
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inode_lock(d_inode(root));
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/* If we have already created ptmx node, return */
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if (fsi->ptmx_dentry) {
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rc = 0;
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goto out;
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}
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dentry = d_alloc_name(root, "ptmx");
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if (!dentry) {
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pr_err("Unable to alloc dentry for ptmx node\n");
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goto out;
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}
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/*
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* Create a new 'ptmx' node in this mount of devpts.
|
*/
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inode = new_inode(sb);
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if (!inode) {
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pr_err("Unable to alloc inode for ptmx node\n");
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dput(dentry);
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goto out;
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}
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inode->i_ino = 2;
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inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
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mode = S_IFCHR|opts->ptmxmode;
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init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
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inode->i_uid = ptmx_uid;
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inode->i_gid = ptmx_gid;
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d_add(dentry, inode);
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fsi->ptmx_dentry = dentry;
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rc = 0;
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out:
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inode_unlock(d_inode(root));
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return rc;
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}
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static void update_ptmx_mode(struct pts_fs_info *fsi)
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{
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struct inode *inode;
|
if (fsi->ptmx_dentry) {
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inode = d_inode(fsi->ptmx_dentry);
|
inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
|
}
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}
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static int devpts_remount(struct super_block *sb, int *flags, char *data)
|
{
|
int err;
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
|
struct pts_mount_opts *opts = &fsi->mount_opts;
|
|
err = parse_mount_options(data, PARSE_REMOUNT, opts);
|
|
/*
|
* parse_mount_options() restores options to default values
|
* before parsing and may have changed ptmxmode. So, update the
|
* mode in the inode too. Bogus options don't fail the remount,
|
* so do this even on error return.
|
*/
|
update_ptmx_mode(fsi);
|
|
return err;
|
}
|
|
static int devpts_show_options(struct seq_file *seq, struct dentry *root)
|
{
|
struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
|
struct pts_mount_opts *opts = &fsi->mount_opts;
|
|
if (opts->setuid)
|
seq_printf(seq, ",uid=%u",
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from_kuid_munged(&init_user_ns, opts->uid));
|
if (opts->setgid)
|
seq_printf(seq, ",gid=%u",
|
from_kgid_munged(&init_user_ns, opts->gid));
|
seq_printf(seq, ",mode=%03o", opts->mode);
|
seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
|
if (opts->max < NR_UNIX98_PTY_MAX)
|
seq_printf(seq, ",max=%d", opts->max);
|
|
return 0;
|
}
|
|
static const struct super_operations devpts_sops = {
|
.statfs = simple_statfs,
|
.remount_fs = devpts_remount,
|
.show_options = devpts_show_options,
|
};
|
|
static void *new_pts_fs_info(struct super_block *sb)
|
{
|
struct pts_fs_info *fsi;
|
|
fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
|
if (!fsi)
|
return NULL;
|
|
ida_init(&fsi->allocated_ptys);
|
fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
|
fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
|
fsi->sb = sb;
|
|
return fsi;
|
}
|
|
static int
|
devpts_fill_super(struct super_block *s, void *data, int silent)
|
{
|
struct inode *inode;
|
int error;
|
|
s->s_iflags &= ~SB_I_NODEV;
|
s->s_blocksize = 1024;
|
s->s_blocksize_bits = 10;
|
s->s_magic = DEVPTS_SUPER_MAGIC;
|
s->s_op = &devpts_sops;
|
s->s_d_op = &simple_dentry_operations;
|
s->s_time_gran = 1;
|
|
error = -ENOMEM;
|
s->s_fs_info = new_pts_fs_info(s);
|
if (!s->s_fs_info)
|
goto fail;
|
|
error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
|
if (error)
|
goto fail;
|
|
error = -ENOMEM;
|
inode = new_inode(s);
|
if (!inode)
|
goto fail;
|
inode->i_ino = 1;
|
inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
|
inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
|
inode->i_op = &simple_dir_inode_operations;
|
inode->i_fop = &simple_dir_operations;
|
set_nlink(inode, 2);
|
|
s->s_root = d_make_root(inode);
|
if (!s->s_root) {
|
pr_err("get root dentry failed\n");
|
goto fail;
|
}
|
|
error = mknod_ptmx(s);
|
if (error)
|
goto fail_dput;
|
|
return 0;
|
fail_dput:
|
dput(s->s_root);
|
s->s_root = NULL;
|
fail:
|
return error;
|
}
|
|
/*
|
* devpts_mount()
|
*
|
* Mount a new (private) instance of devpts. PTYs created in this
|
* instance are independent of the PTYs in other devpts instances.
|
*/
|
static struct dentry *devpts_mount(struct file_system_type *fs_type,
|
int flags, const char *dev_name, void *data)
|
{
|
return mount_nodev(fs_type, flags, data, devpts_fill_super);
|
}
|
|
static void devpts_kill_sb(struct super_block *sb)
|
{
|
struct pts_fs_info *fsi = DEVPTS_SB(sb);
|
|
if (fsi)
|
ida_destroy(&fsi->allocated_ptys);
|
kfree(fsi);
|
kill_litter_super(sb);
|
}
|
|
static struct file_system_type devpts_fs_type = {
|
.name = "devpts",
|
.mount = devpts_mount,
|
.kill_sb = devpts_kill_sb,
|
.fs_flags = FS_USERNS_MOUNT,
|
};
|
|
/*
|
* The normal naming convention is simply /dev/pts/<number>; this conforms
|
* to the System V naming convention
|
*/
|
|
int devpts_new_index(struct pts_fs_info *fsi)
|
{
|
int index = -ENOSPC;
|
|
if (atomic_inc_return(&pty_count) >= (pty_limit -
|
(fsi->mount_opts.reserve ? 0 : pty_reserve)))
|
goto out;
|
|
index = ida_alloc_max(&fsi->allocated_ptys, fsi->mount_opts.max - 1,
|
GFP_KERNEL);
|
|
out:
|
if (index < 0)
|
atomic_dec(&pty_count);
|
return index;
|
}
|
|
void devpts_kill_index(struct pts_fs_info *fsi, int idx)
|
{
|
ida_free(&fsi->allocated_ptys, idx);
|
atomic_dec(&pty_count);
|
}
|
|
/**
|
* devpts_pty_new -- create a new inode in /dev/pts/
|
* @ptmx_inode: inode of the master
|
* @device: major+minor of the node to be created
|
* @index: used as a name of the node
|
* @priv: what's given back by devpts_get_priv
|
*
|
* The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
|
*/
|
struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
|
{
|
struct dentry *dentry;
|
struct super_block *sb = fsi->sb;
|
struct inode *inode;
|
struct dentry *root;
|
struct pts_mount_opts *opts;
|
char s[12];
|
|
root = sb->s_root;
|
opts = &fsi->mount_opts;
|
|
inode = new_inode(sb);
|
if (!inode)
|
return ERR_PTR(-ENOMEM);
|
|
inode->i_ino = index + 3;
|
inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
|
inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
|
inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
|
init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
|
|
sprintf(s, "%d", index);
|
|
dentry = d_alloc_name(root, s);
|
if (dentry) {
|
dentry->d_fsdata = priv;
|
d_add(dentry, inode);
|
fsnotify_create(d_inode(root), dentry);
|
} else {
|
iput(inode);
|
dentry = ERR_PTR(-ENOMEM);
|
}
|
|
return dentry;
|
}
|
|
/**
|
* devpts_get_priv -- get private data for a slave
|
* @pts_inode: inode of the slave
|
*
|
* Returns whatever was passed as priv in devpts_pty_new for a given inode.
|
*/
|
void *devpts_get_priv(struct dentry *dentry)
|
{
|
if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
|
return NULL;
|
return dentry->d_fsdata;
|
}
|
|
/**
|
* devpts_pty_kill -- remove inode form /dev/pts/
|
* @inode: inode of the slave to be removed
|
*
|
* This is an inverse operation of devpts_pty_new.
|
*/
|
void devpts_pty_kill(struct dentry *dentry)
|
{
|
WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
|
|
dentry->d_fsdata = NULL;
|
drop_nlink(dentry->d_inode);
|
d_drop(dentry);
|
fsnotify_unlink(d_inode(dentry->d_parent), dentry);
|
dput(dentry); /* d_alloc_name() in devpts_pty_new() */
|
}
|
|
static int __init init_devpts_fs(void)
|
{
|
int err = register_filesystem(&devpts_fs_type);
|
if (!err) {
|
register_sysctl_table(pty_root_table);
|
}
|
return err;
|
}
|
module_init(init_devpts_fs)
|
