![Eric W. Biederman](/assets/img/avatar_default.png)
The implementation of TIOCGPTPEER has two issues. When /dev/ptmx (as opposed to /dev/pts/ptmx) is opened the wrong vfsmount is passed to dentry_open. Which results in the kernel displaying the wrong pathname for the peer. The second is simply by caching the vfsmount and dentry of the peer it leaves them open, in a way they were not previously Which because of the inreased reference counts can cause unnecessary behaviour differences resulting in regressions. To fix these move the ioctl into tty_io.c at a generic level allowing the ioctl to have access to the struct file on which the ioctl is being called. This allows the path of the slave to be derived when opening the slave through TIOCGPTPEER instead of requiring the path to the slave be cached. Thus removing the need for caching the path. A new function devpts_ptmx_path is factored out of devpts_acquire and used to implement a function devpts_mntget. The new function devpts_mntget takes a filp to perform the lookup on and fsi so that it can confirm that the superblock that is found by devpts_ptmx_path is the proper superblock. v2: Lots of fixes to make the code actually work v3: Suggestions by Linus - Removed the unnecessary initialization of filp in ptm_open_peer - Simplified devpts_ptmx_path as gotos are no longer required [ This is the fix for the issue that was reverted in commit143c97cc65
, but this time without breaking 'pbuilder' due to increased reference counts - Linus ] Fixes:54ebbfb160
("tty: add TIOCGPTPEER ioctl") Reported-by: Christian Brauner <christian.brauner@canonical.com> Reported-and-tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
632 lines
14 KiB
C
632 lines
14 KiB
C
/* -*- 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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* This file is part of the Linux kernel and is made available under
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* the terms of the GNU General Public License, version 2, or at your
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* option, any later version, incorporated herein by reference.
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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 int pty_count;
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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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static DEFINE_MUTEX(allocated_ptys_lock);
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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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/* 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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return 0;
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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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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;
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path = filp->f_path;
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path_get(&path);
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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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mntput(path.mnt);
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path.mnt = ERR_PTR(err);
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}
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if (DEVPTS_SB(path.mnt->mnt_sb) != fsi) {
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mntput(path.mnt);
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path.mnt = ERR_PTR(-ENODEV);
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}
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return path.mnt;
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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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int err;
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path = filp->f_path;
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path_get(&path);
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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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* 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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*/
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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;
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if (fsi->ptmx_dentry) {
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inode = d_inode(fsi->ptmx_dentry);
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inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
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}
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}
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static int devpts_remount(struct super_block *sb, int *flags, char *data)
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{
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int err;
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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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err = parse_mount_options(data, PARSE_REMOUNT, opts);
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/*
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* parse_mount_options() restores options to default values
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* before parsing and may have changed ptmxmode. So, update the
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* mode in the inode too. Bogus options don't fail the remount,
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* so do this even on error return.
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*/
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update_ptmx_mode(fsi);
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return err;
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}
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static int devpts_show_options(struct seq_file *seq, struct dentry *root)
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{
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struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
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struct pts_mount_opts *opts = &fsi->mount_opts;
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if (opts->setuid)
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seq_printf(seq, ",uid=%u",
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from_kuid_munged(&init_user_ns, opts->uid));
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if (opts->setgid)
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seq_printf(seq, ",gid=%u",
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from_kgid_munged(&init_user_ns, opts->gid));
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seq_printf(seq, ",mode=%03o", opts->mode);
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seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
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if (opts->max < NR_UNIX98_PTY_MAX)
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seq_printf(seq, ",max=%d", opts->max);
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return 0;
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}
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static const struct super_operations devpts_sops = {
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.statfs = simple_statfs,
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.remount_fs = devpts_remount,
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.show_options = devpts_show_options,
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};
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static void *new_pts_fs_info(struct super_block *sb)
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{
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struct pts_fs_info *fsi;
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fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
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if (!fsi)
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return NULL;
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ida_init(&fsi->allocated_ptys);
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fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
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fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
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fsi->sb = sb;
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return fsi;
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}
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static int
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devpts_fill_super(struct super_block *s, void *data, int silent)
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{
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struct inode *inode;
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int error;
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s->s_iflags &= ~SB_I_NODEV;
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s->s_blocksize = 1024;
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s->s_blocksize_bits = 10;
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s->s_magic = DEVPTS_SUPER_MAGIC;
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s->s_op = &devpts_sops;
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s->s_time_gran = 1;
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error = -ENOMEM;
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s->s_fs_info = new_pts_fs_info(s);
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if (!s->s_fs_info)
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goto fail;
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error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
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if (error)
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goto fail;
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error = -ENOMEM;
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inode = new_inode(s);
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if (!inode)
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goto fail;
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inode->i_ino = 1;
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inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
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inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
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inode->i_op = &simple_dir_inode_operations;
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inode->i_fop = &simple_dir_operations;
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set_nlink(inode, 2);
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s->s_root = d_make_root(inode);
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if (!s->s_root) {
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pr_err("get root dentry failed\n");
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goto fail;
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}
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error = mknod_ptmx(s);
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if (error)
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goto fail_dput;
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return 0;
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fail_dput:
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dput(s->s_root);
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s->s_root = NULL;
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fail:
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return error;
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}
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/*
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* devpts_mount()
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*
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* Mount a new (private) instance of devpts. PTYs created in this
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* instance are independent of the PTYs in other devpts instances.
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*/
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static struct dentry *devpts_mount(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data)
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{
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return mount_nodev(fs_type, flags, data, devpts_fill_super);
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}
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static void devpts_kill_sb(struct super_block *sb)
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{
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
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if (fsi)
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ida_destroy(&fsi->allocated_ptys);
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kfree(fsi);
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kill_litter_super(sb);
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}
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static struct file_system_type devpts_fs_type = {
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.name = "devpts",
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.mount = devpts_mount,
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.kill_sb = devpts_kill_sb,
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.fs_flags = FS_USERNS_MOUNT,
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};
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/*
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* The normal naming convention is simply /dev/pts/<number>; this conforms
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* to the System V naming convention
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*/
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int devpts_new_index(struct pts_fs_info *fsi)
|
|
{
|
|
int index;
|
|
int ida_ret;
|
|
|
|
retry:
|
|
if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
|
|
return -ENOMEM;
|
|
|
|
mutex_lock(&allocated_ptys_lock);
|
|
if (pty_count >= (pty_limit -
|
|
(fsi->mount_opts.reserve ? 0 : pty_reserve))) {
|
|
mutex_unlock(&allocated_ptys_lock);
|
|
return -ENOSPC;
|
|
}
|
|
|
|
ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
|
|
if (ida_ret < 0) {
|
|
mutex_unlock(&allocated_ptys_lock);
|
|
if (ida_ret == -EAGAIN)
|
|
goto retry;
|
|
return -EIO;
|
|
}
|
|
|
|
if (index >= fsi->mount_opts.max) {
|
|
ida_remove(&fsi->allocated_ptys, index);
|
|
mutex_unlock(&allocated_ptys_lock);
|
|
return -ENOSPC;
|
|
}
|
|
pty_count++;
|
|
mutex_unlock(&allocated_ptys_lock);
|
|
return index;
|
|
}
|
|
|
|
void devpts_kill_index(struct pts_fs_info *fsi, int idx)
|
|
{
|
|
mutex_lock(&allocated_ptys_lock);
|
|
ida_remove(&fsi->allocated_ptys, idx);
|
|
pty_count--;
|
|
mutex_unlock(&allocated_ptys_lock);
|
|
}
|
|
|
|
/**
|
|
* 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_delete(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)
|