This is a note to let you know that I've just added the patch titled
Subject: devpts_get_tty() should validate inode
to my gregkh-2.6 tree. Its filename is
devpts_get_tty-should-validate-inode.patch
This tree can be found at
http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/
>From sukadev@xxxxxxxxxxxxxxxxxx Thu Nov 19 15:40:33 2009
From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Date: Tue, 17 Nov 2009 18:35:43 -0800
Subject: devpts_get_tty() should validate inode
To: gregkh@xxxxxxx
Cc: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>, hpa@xxxxxxxxx, root@xxxxxxxxxxxxxx, sukadev@xxxxxxxxxxxxxxxxxx, Containers <containers@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Message-ID: <20091118023541.GA14430@xxxxxxxxxx>
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@xxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Tested-by: Serge Hallyn <serue@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
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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