Shaun Reitan
2010-Nov-22 16:27 UTC
[Xen-devel] [PATCH] fs: pipe.c null pointer dereference - CVE-2009-3547
We''ve been applying this patch since the fix was discovered but i just
realized yesterday when building a new kernel that the Xen kernel does
not have this fix applied yet.
I also have verified that this exploit works to gain root access on the
current http://xenbits.xensource.com/linux-2.6.18-xen.hg branch
--
Shaun Retian
Chief Technical Officer
Network Data Center Host, Inc.
http://www.ndchost.com
-- PATCH --
From ad3960243e55320d74195fb85c975e0a8cc4466c Mon Sep 17 00:00:00 2001
From: Earl Chew <earl_chew@agilent.com>
Date: Mon, 19 Oct 2009 15:55:41 -0700
Subject: [PATCH] fs: pipe.c null pointer dereference
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:
> [<ffffffff802899a5>] pipe_rdwr_open+0x35/0x70
> [<ffffffff8028125c>] __dentry_open+0x13c/0x230
> [<ffffffff8028143d>] do_filp_open+0x2d/0x40
> [<ffffffff802814aa>] do_sys_open+0x5a/0x100
> [<ffffffff8021faf3>] 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 <earl_chew@agilent.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/pipe.c | 41 ++++++++++++++++++++++++++++++-----------
1 files changed, 30 insertions(+), 11 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c
index 52c4151..ae17d02 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -777,36 +777,55 @@ pipe_rdwr_release(struct inode *inode, struct file
*filp)
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;
}
/*
--
1.7.3.2
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Keir Fraser
2010-Nov-22 19:24 UTC
Re: [Xen-devel] [PATCH] fs: pipe.c null pointer dereference - CVE-2009-3547
On 22/11/2010 16:27, "Shaun Reitan" <mailinglists@unix-scripts.com> wrote:> We''ve been applying this patch since the fix was discovered but i just > realized yesterday when building a new kernel that the Xen kernel does > not have this fix applied yet. > > I also have verified that this exploit works to gain root access on the > current http://xenbits.xensource.com/linux-2.6.18-xen.hg branchIt has to be said, very clearly, that our 2.6.18 tree is only really of use now as a repository of Xen patches for vendors to pull into their own, *properly maintained and secured* kernels. We are very interested in fixing Xen-related security issues in our 2.6.18 tree (precisely because others use it as a repository of good Xen patches). We are less interested in general kernel fixes, although of course as a matter of good form we will consider a security fix such as you propose. However, the patch you supplied does not apply to the 2.6.18 tree. Thanks, Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Shaun Reitan
2010-Nov-22 20:30 UTC
[Xen-devel] Re: [PATCH] fs: pipe.c null pointer dereference - CVE-2009-3547
On 11/22/2010 11:24 AM, Keir Fraser wrote:> On 22/11/2010 16:27, "Shaun Reitan"<mailinglists@unix-scripts.com> wrote: > >> We''ve been applying this patch since the fix was discovered but i just >> realized yesterday when building a new kernel that the Xen kernel does >> not have this fix applied yet. >> >> I also have verified that this exploit works to gain root access on the >> current http://xenbits.xensource.com/linux-2.6.18-xen.hg branch > > It has to be said, very clearly, that our 2.6.18 tree is only really of use > now as a repository of Xen patches for vendors to pull into their own, > *properly maintained and secured* kernels. We are very interested in fixing > Xen-related security issues in our 2.6.18 tree (precisely because others use > it as a repository of good Xen patches). We are less interested in general > kernel fixes, although of course as a matter of good form we will consider a > security fix such as you propose. However, the patch you supplied does not > apply to the 2.6.18 tree. > > Thanks, > KeirI see, good to know, thanks! -- Shaun Retian Chief Technical Officer Network Data Center Host, Inc. http://www.ndchost.com _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel