oss-security - CVE REQUEST: linux kernel: process with pgid zero able to crash kernel

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Message-ID: <1484880112.11949.24.camel@redhat.com>
Date: Fri, 20 Jan 2017 13:41:52 +1100
From: Harshula <harshula@...hat.com>
To: oss-security@...ts.openwall.com
Cc: Jesse Hertz <Jesse.Hertz@...group.trust>,
        Wade Mealing
 <wmealing@...hat.com>
Subject: CVE REQUEST: linux kernel: process with pgid zero able to crash
 kernel

Hi Folks,

Red Hat Product Security has been notified of a kernel vulnerability
that a local attacker can exploit to crash/panic the kernel and cause a
denial of service.

This was reported to Red Hat by Jesse Hertz (CC'd) (reproducer:
rt411016):

"A process that is in the same process group as the ``init'' process
(group id zero) can crash the Linux 2 kernel with several system calls
by passing in a process ID or process group ID of zero. The value zero
is a special value that indicates the current process ID or process
group. However, in this case it is also the process group ID of the
process."

I've been testing whether RHEL is vulnerable and found the following:

* Upstream/mainline is not vulnerable
* RHEL 7 is not vulnerable
* RHEL 6 is vulnerable
* RHEL 5 is partially vulnerable

A very specific set of circumstances are required in order for the
vulnerability to be exploited. The default configuration of RHEL 5 and
RHEL 6 are not exploitable.

The risk is that a non-root user can trigger a kernel crash on a
modified RHEL 6 system where the kernel runs a process that can be
exploited. Perhaps on an embedded device.

Thanks,
Harshula

Red Hat Bugzilla:
https://bugzilla.redhat.com/show_bug.cgi?id=1358840

Patches:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/
?id=f106eee10038c2ee5b6056aaf3f6d5229be6dcdd
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/
?id=f20011457f41c11edb5ea5038ad0c8ea9f392023
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/
?id=fa2755e20ab0c7215d99c2dc7c262e98a09b01df

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