From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932186AbZKFWFt (ORCPT ); Fri, 6 Nov 2009 17:05:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932145AbZKFWFr (ORCPT ); Fri, 6 Nov 2009 17:05:47 -0500 Received: from kroah.org ([198.145.64.141]:39721 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759906AbZKFWFo (ORCPT ); Fri, 6 Nov 2009 17:05:44 -0500 X-Mailbox-Line: From gregkh@mini.kroah.org Fri Nov 6 13:59:50 2009 Message-Id: <20091106215950.827974192@mini.kroah.org> User-Agent: quilt/0.48-1 Date: Fri, 06 Nov 2009 13:56:09 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Earl Chew Subject: [06/30] fs: pipe.c null pointer dereference References: <20091106215603.413650799@mini.kroah.org> Content-Disposition: inline; filename=fs-pipe.c-null-pointer-dereference.patch In-Reply-To: <20091106220156.GA13813@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.29-stable review patch. If anyone has any objections, please let us know. ------------------ From: Earl Chew commit ad3960243e55320d74195fb85c975e0a8cc4466c upstream. This patch fixes a null pointer exception in pipe_rdwr_open() which generates the stack trace: > Unable to handle kernel NULL pointer dereference at 0000000000000028 RIP: > [] pipe_rdwr_open+0x35/0x70 > [] __dentry_open+0x13c/0x230 > [] do_filp_open+0x2d/0x40 > [] do_sys_open+0x5a/0x100 > [] sysenter_do_call+0x1b/0x67 The failure mode is triggered by an attempt to open an anonymous pipe via /proc/pid/fd/* as exemplified by this script: ============================================================= while : ; do { echo y ; sleep 1 ; } | { while read ; do echo z$REPLY; done ; } & PID=$! OUT=$(ps -efl | grep 'sleep 1' | grep -v grep | { read PID REST ; echo $PID; } ) OUT="${OUT%% *}" DELAY=$((RANDOM * 1000 / 32768)) usleep $((DELAY * 1000 + RANDOM % 1000 )) echo n > /proc/$OUT/fd/1 # Trigger defect done ============================================================= Note that the failure window is quite small and I could only reliably reproduce the defect by inserting a small delay in pipe_rdwr_open(). For example: static int pipe_rdwr_open(struct inode *inode, struct file *filp) { msleep(100); mutex_lock(&inode->i_mutex); Although the defect was observed in pipe_rdwr_open(), I think it makes sense to replicate the change through all the pipe_*_open() functions. The core of the change is to verify that inode->i_pipe has not been released before attempting to manipulate it. If inode->i_pipe is no longer present, return ENOENT to indicate so. The comment about potentially using atomic_t for i_pipe->readers and i_pipe->writers has also been removed because it is no longer relevant in this context. The inode->i_mutex lock must be used so that inode->i_pipe can be dealt with correctly. Signed-off-by: Earl Chew Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/pipe.c | 41 ++++++++++++++++++++++++++++++----------- 1 file changed, 30 insertions(+), 11 deletions(-) --- a/fs/pipe.c +++ b/fs/pipe.c @@ -742,36 +742,55 @@ pipe_rdwr_release(struct inode *inode, s static int pipe_read_open(struct inode *inode, struct file *filp) { - /* We could have perhaps used atomic_t, but this and friends - below are the only places. So it doesn't seem worthwhile. */ + int ret = -ENOENT; + mutex_lock(&inode->i_mutex); - inode->i_pipe->readers++; + + if (inode->i_pipe) { + ret = 0; + inode->i_pipe->readers++; + } + mutex_unlock(&inode->i_mutex); - return 0; + return ret; } static int pipe_write_open(struct inode *inode, struct file *filp) { + int ret = -ENOENT; + mutex_lock(&inode->i_mutex); - inode->i_pipe->writers++; + + if (inode->i_pipe) { + ret = 0; + inode->i_pipe->writers++; + } + mutex_unlock(&inode->i_mutex); - return 0; + return ret; } static int pipe_rdwr_open(struct inode *inode, struct file *filp) { + int ret = -ENOENT; + mutex_lock(&inode->i_mutex); - if (filp->f_mode & FMODE_READ) - inode->i_pipe->readers++; - if (filp->f_mode & FMODE_WRITE) - inode->i_pipe->writers++; + + if (inode->i_pipe) { + ret = 0; + if (filp->f_mode & FMODE_READ) + inode->i_pipe->readers++; + if (filp->f_mode & FMODE_WRITE) + inode->i_pipe->writers++; + } + mutex_unlock(&inode->i_mutex); - return 0; + return ret; } /*