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    Subject[060/151] devpts_get_tty() should validate inode
    2.6.32-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>

    commit edfacdd6f81119b9005615593f2cbd94b8c7e2d8 upstream.

    devpts_get_tty() assumes that the inode passed in is associated with a valid
    pty. But if the only reference to the pty is via a bind-mount, the inode
    passed to devpts_get_tty() while valid, would refer to a pty that no longer
    exists.

    With a lot of debug effort, Grzegorz Nosek developed a small program (see
    below) to reproduce a crash on recent kernels. This crash is a regression
    introduced by the commit:

    commit 527b3e4773628b30d03323a2cb5fb0d84441990f
    Author: Sukadev Bhattiprolu <sukadev@us.ibm.com>
    Date: Mon Oct 13 10:43:08 2008 +0100

    To fix, ensure that the dentry associated with the inode has not yet been
    deleted/unhashed by devpts_pty_kill().

    See also:
    https://lists.linux-foundation.org/pipermail/containers/2009-July/019273.html

    tty-bug.c:

    #define _GNU_SOURCE
    #include <fcntl.h>
    #include <sched.h>
    #include <stdlib.h>
    #include <sys/mount.h>
    #include <sys/signal.h>
    #include <unistd.h>
    #include <stdio.h>

    #include <linux/fs.h>

    void dummy(int sig)
    {
    }

    static int child(void *unused)
    {
    int fd;

    signal(SIGINT, dummy); signal(SIGHUP, dummy);
    pause(); /* cheesy synchronisation to wait for /dev/pts/0 to appear */

    mount("/dev/pts/0", "/dev/console", NULL, MS_BIND, NULL);
    sleep(2);

    fd = open("/dev/console", O_RDWR);
    dup(0); dup(0);
    write(1, "Hello world!\n", sizeof("Hello world!\n")-1);
    return 0;
    }

    int main(void)
    {
    pid_t pid;
    char *stack;

    stack = malloc(16384);
    pid = clone(child, stack+16384, CLONE_NEWNS|SIGCHLD, NULL);

    open("/dev/ptmx", O_RDWR|O_NOCTTY|O_NONBLOCK);

    unlockpt(fd); grantpt(fd);

    sleep(2);
    kill(pid, SIGHUP);
    sleep(1);
    return 0; /* exit before child opens /dev/console */
    }

    Reported-by: Grzegorz Nosek <root@localdomain.pl>
    Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
    Tested-by: Serge Hallyn <serue@us.ibm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/devpts/inode.c | 16 ++++++++++++++--
    1 file changed, 14 insertions(+), 2 deletions(-)

    --- a/fs/devpts/inode.c
    +++ b/fs/devpts/inode.c
    @@ -517,11 +517,23 @@ int devpts_pty_new(struct inode *ptmx_in

    struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
    {
    + struct dentry *dentry;
    + struct tty_struct *tty;
    +
    BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));

    + /* Ensure dentry has not been deleted by devpts_pty_kill() */
    + dentry = d_find_alias(pts_inode);
    + if (!dentry)
    + return NULL;
    +
    + tty = NULL;
    if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
    - return (struct tty_struct *)pts_inode->i_private;
    - return NULL;
    + tty = (struct tty_struct *)pts_inode->i_private;
    +
    + dput(dentry);
    +
    + return tty;
    }

    void devpts_pty_kill(struct tty_struct *tty)



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