forked from Minki/linux
73052b0dae
d_delete only unhashes an entry if it is reached with dentry->d_lockref.count != 1. Prior to commit8ead9dd547
("devpts: more pty driver interface cleanups"), d_delete was called on a dentry from devpts_pty_kill with two references held, which would trigger the unhashing, and the subsequent dputs would release it. Commit8ead9dd547
reworked devpts_pty_kill to stop acquiring the second reference from d_find_alias, and the d_delete call left the dentries still on the hashed list without actually ever being dropped from dcache before explicit cleanup. This causes the number of negative dentries for devpts to pile up, and an `ls /dev/pts` invocation can take seconds to return. Provide always_delete_dentry() from simple_dentry_operations as .d_delete for devpts, to make the dentry be dropped from dcache. Without this cleanup, the number of dentries in /dev/pts/ can be grown arbitrarily as: `python -c 'import pty; pty.spawn(["ls", "/dev/pts"])'` A systemtap probe on dcache_readdir to count d_subdirs shows this count to increase with each pty spawn invocation above: probe kernel.function("dcache_readdir") { subdirs = &@cast($file->f_path->dentry, "dentry")->d_subdirs; p = subdirs; p = @cast(p, "list_head")->next; i = 0 while (p != subdirs) { p = @cast(p, "list_head")->next; i = i+1; } printf("number of dentries: %d\n", i); } Fixes:8ead9dd547
("devpts: more pty driver interface cleanups") Signed-off-by: Varad Gautam <vrd@amazon.de> Reported-by: Zheng Wang <wanz@amazon.de> Reported-by: Brandon Schwartz <bsschwar@amazon.de> Root-caused-by: Maximilian Heyne <mheyne@amazon.de> Root-caused-by: Nicolas Pernas Maradei <npernas@amazon.de> CC: David Woodhouse <dwmw@amazon.co.uk> CC: Maximilian Heyne <mheyne@amazon.de> CC: Stefan Nuernberger <snu@amazon.de> CC: Amit Shah <aams@amazon.de> CC: Linus Torvalds <torvalds@linux-foundation.org> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org> CC: Al Viro <viro@ZenIV.linux.org.uk> CC: Christian Brauner <christian.brauner@ubuntu.com> CC: Eric W. Biederman <ebiederm@xmission.com> CC: Matthew Wilcox <willy@infradead.org> CC: Eric Biggers <ebiggers@google.com> CC: <stable@vger.kernel.org> # 4.9+ Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
640 lines
15 KiB
C
640 lines
15 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 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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*/
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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_d_op = &simple_dentry_operations;
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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;
|
|
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_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)
|