From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753977AbZKRCfX (ORCPT ); Tue, 17 Nov 2009 21:35:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752825AbZKRCfX (ORCPT ); Tue, 17 Nov 2009 21:35:23 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:47352 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752730AbZKRCfW (ORCPT ); Tue, 17 Nov 2009 21:35:22 -0500 Date: Tue, 17 Nov 2009 18:35:43 -0800 From: Sukadev Bhattiprolu To: gregkh@suse.de Cc: Alan Cox , hpa@zytor.com, root@localdomain.pl, sukadev@linux.vnet.ibm.com, Containers , linux-kernel@vger.kernel.org Subject: [PATCH] devpts_get_tty() should validate inode Message-ID: <20091118023541.GA14430@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Operating-System: Linux 2.0.32 on an i486 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 #include #include #include #include #include #include #include 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 Signed-off-by: Sukadev Bhattiprolu --- Index: linux-2.6/fs/devpts/inode.c =================================================================== --- linux-2.6.orig/fs/devpts/inode.c 2009-10-20 21:11:03.000000000 -0700 +++ linux-2.6/fs/devpts/inode.c 2009-11-17 16:07:16.000000000 -0800 @@ -517,11 +517,23 @@ 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)