Bug 527865 - (CVE-2009-2848) VUL-1: CVE-2009-2848: kernel: execve: must clear current->clear_child_tid
VUL-1: CVE-2009-2848: kernel: execve: must clear current->clear_child_tid
Classification: Novell Products
Product: SUSE Security Incidents
Classification: Novell Products
Component: Incidents
Other Other
: P2 - High : Major
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Assigned To: Security Team bot
Security Team bot
wasL3:29692 CVE-2009-2848: CVSS v2 Ba...
Depends on:
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Reported: 2009-08-04 08:30 UTC by Thomas Biege
Modified: 2020-04-20 12:29 UTC (History)
7 users (show)

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Found By: Development
Services Priority: 800
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Description Thomas Biege 2009-08-04 08:30:04 UTC
There is a security bug in 'kernel'.

This information is from 'oss-security'.

This bug is public.

There is no coordinated release date (CRD) set.

More information can be found here:

Original posting:

----- Forwarded message from Eugene Teo <eugene@redhat.com> -----

Reply-To: oss-security@lists.openwall.com
Date: Tue, 04 Aug 2009 16:09:09 +0800
From: Eugene Teo <eugene@redhat.com>
User-Agent: Thunderbird (X11/20090320)
To: oss-security@lists.openwall.com
Cc: "Steven M. Christey" <coley@linus.mitre.org>
Subject: [oss-security] CVE request - kernel: execve: must clear current->clear_child_tid

clone() syscall has special support for TID of created threads.  This
support includes two features.

One (CLONE_CHILD_SETTID) is to set an integer into user memory with the
TID value.

One (CLONE_CHILD_CLEARTID) is to clear this same integer once the
created thread dies.

The integer location is a user provided pointer, provided at clone() time.

kernel keeps this pointer value into current->clear_child_tid.

At execve() time, we should make sure kernel doesnt keep this user
provided pointer, as full user memory is replaced by a new one.

As glibc fork() actually uses clone() syscall with CLONE_CHILD_SETTID
and CLONE_CHILD_CLEARTID set, chances are high that we might corrupt
user memory in forked processes.

Following sequence could happen:

1) bash (or any program) starts a new process, by a fork() call that
glibc maps to a clone( ...  CLONE_CHILD_SETTID |

2) When new process starts, its current->clear_child_tid is set to a
location that has a meaning only in bash (or initial program) context

3) This new process does the execve() syscall to start a new program.
current->clear_child_tid is left unchanged (a non NULL value)

4) If this new program creates some threads, and initial thread exits,
kernel will attempt to clear the integer pointed by
current->clear_child_tid from mm_release() :

        if (tsk->clear_child_tid
            && !(tsk->flags & PF_SIGNALED)
            && atomic_read(&mm->mm_users) > 1) {
                u32 __user * tidptr = tsk->clear_child_tid;
                tsk->clear_child_tid = NULL;

                 * We don't check the error code - if userspace has
                 * not set up a proper pointer then tough luck.
<< here >>      put_user(0, tidptr);
                sys_futex(tidptr, FUTEX_WAKE, 1, NULL, NULL, 0);

5) OR : if new program is not multi-threaded, but spied by /proc/pid
users (ps command for example), mm_users > 1, and the exiting program
could corrupt 4 bytes in a persistent memory area (shm or memory mapped

If current->clear_child_tid points to a writeable portion of memory of
the new program, kernel happily and silently corrupts 4 bytes of memory,
with unexpected effects.


Patch is not in upstream kernel yet.

Thanks, Eugene

----- End forwarded message -----
Comment 2 Ludwig Nussel 2009-08-20 08:03:39 UTC
Name: CVE-2009-2848
Status: Candidate
URL: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-2848
Reference: MLIST:[linux-kernel] 20090801 [PATCH v2] execve: must clear current->clear_child_tid
Reference: URL:http://article.gmane.org/gmane.linux.kernel/871942
Reference: MLIST:[oss-security] 20090804 CVE request - kernel: execve: must clear current->clear_child_tid
Reference: URL:http://www.openwall.com/lists/oss-security/2009/08/04/2
Reference: MLIST:[oss-security] 20090805 Re: CVE request - kernel: execve: must clear current->clear_child_tid
Reference: URL:http://www.openwall.com/lists/oss-security/2009/08/05/10

The execve function in the Linux kernel, possibly 2.6.30-rc6 and
earlier, does not properly clear the current->clear_child_tid pointer,
which allows local users to cause a denial of service (memory
corruption) via a clone system call with CLONE_CHILD_SETTID or
CLONE_CHILD_CLEARTID enabled, which is not properly handled during
thread creation and exit.
Comment 3 Jeff Mahoney 2009-09-02 18:23:17 UTC
This fix will be part of the next SLE11 update via the sync.

Comment 4 Thomas Biege 2009-10-14 02:49:17 UTC
CVE-2009-2848: CVSS v2 Base Score: 4.7 (AV:L/AC:M/Au:N/C:N/I:N/A:C)
Comment 5 Swamp Workflow Management 2009-11-10 23:09:46 UTC
Update released for: kernel-debug, kernel-debug-debuginfo, kernel-default, kernel-default-debuginfo, kernel-source, kernel-source-debuginfo, kernel-syms
SLE-SDK 10-SP2 (ia64)
SLE-SERVER 10-SP2 (ia64)
Comment 6 Swamp Workflow Management 2009-11-11 23:10:05 UTC
Update released for: kernel-default, kernel-default-debuginfo, kernel-source, kernel-syms
SLE-DEBUGINFO 10-SP2 (s390x)
SLE-SERVER 10-SP2 (s390x)
Comment 7 Marcus Meissner 2009-11-12 17:08:43 UTC
A kernel update fixing / mentioning this bug was released on Tuesday, kernel version
Comment 8 Swamp Workflow Management 2009-11-13 23:08:52 UTC
Update released for: kernel-s390, kernel-s390-debug, kernel-source, kernel-syms, um-host-kernel, kernel-update.ycp, install-kernel-non-interactive.sh
SUSE-CORE 9 (s390)
Comment 9 Marcus Meissner 2009-11-16 16:40:46 UTC
A Linux kernel update for SUSE Linux Enterprise Server 9 was released Friday that fixes/mentions this bug. Its version is 2.6.5-7.321.
Comment 10 Swamp Workflow Management 2009-11-18 23:08:53 UTC
Update released for: kernel-bigsmp, kernel-bigsmp-debug, kernel-debug, kernel-debug-debug, kernel-default, kernel-default-debug, kernel-smp, kernel-smp-debug, kernel-source, kernel-syms, kernel-um, kernel-um-debug, kernel-xen, kernel-xen-debug, kernel-xenpae, kernel-xenpae-debug, um-host-install-initrd, um-host-kernel, xen-kmp
Novell-Linux-Desktop 9 (i386)
Open-Enterprise-Server 9 (i386)
Comment 13 Michal Hocko 2009-12-17 12:07:36 UTC
Starting L3 here
Comment 14 Michal Hocko 2009-12-17 12:34:55 UTC
Both patches have been scheduled for the next TD rollup release:
- sles9sp3 - bug 426350 comment 158 and bug 426350 comment 159
- sles10sp1 - bug 434477 comment 121 and bug 434477 comment 122
Comment 15 Michal Hocko 2009-12-17 12:36:10 UTC
L3 done here
Comment 17 Marcus Meissner 2009-12-22 12:55:21 UTC
We released it already in the update

it was fixed in stable patch from upstream, and we missed listing the bug in the changes entry:

Mon Aug 17 17:56:23 CEST 2009 - gregkh@suse.de

- Update to and
  - security fixes
  - lots of bugfixes
  - obsoletes:
    - patches.fixes/net-make-sock_sendpage-use-kernel_sendpage
    - patches.fixes/page-allocator-preserve-pfn-ordering-when-__gfp_cold-is-set.patch

I think its all done.
Comment 18 Swamp Workflow Management 2010-02-15 12:14:15 UTC
Update released for: acerhk-kmp-debug, acx-kmp-debug, appleir-kmp-debug, at76_usb-kmp-debug, atl2-kmp-debug, aufs-kmp-debug, dazuko-kmp-debug, drbd-kmp-debug, gspcav-kmp-debug, iscsitarget-kmp-debug, ivtv-kmp-debug, kernel-debug, kernel-default, kernel-docs, kernel-kdump, kernel-pae, kernel-ppc64, kernel-ps3, kernel-source, kernel-syms, kernel-vanilla, kernel-xen, kqemu-kmp-debug, nouveau-kmp-debug, omnibook-kmp-debug, pcc-acpi-kmp-debug, pcfclock-kmp-debug, tpctl-kmp-debug, uvcvideo-kmp-debug, virtualbox-ose-kmp-debug, vmware-kmp-debug, wlan-ng-kmp-debug
openSUSE 11.0 (debug, i386, ppc, x86_64)