VSR Advisories: Linux RDS Protocol Local Privilege Escalation

2010-10-2400:00:00

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                     VSR Security Advisory
                   http://www.vsecurity.com/

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Advisory Name: Linux RDS Protocol Local Privilege Escalation
Release Date: 2010-10-19
Application: Linux Kernel
Versions: 2.6.30 - 2.6.36-rc8
Severity: High
Author: Dan Rosenberg < drosenberg (at) vsecurity (dot) com >
Vendor Status: Patch Released [3]
CVE Candidate: CVE-2010-3904
Reference: http://www.vsecurity.com/resources/advisory/20101019-1/

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Product Description

From [1]:

"Linux is a free Unix-type operating system originally created by Linus
Torvalds with the assistance of developers around the world. Developed under
the GNU General Public License, the source code for Linux is freely available
to everyone."

From [2]:

"Reliable Datagram Sockets (RDS) provide in order, non-duplicating,
highly available, low overhead, reliable delivery of datagrams between
hundreds of thousands of non-connected endpoints."

Vulnerability Overview

On October 13th, VSR identified a vulnerability in the RDS protocol, as
implemented in the Linux kernel. Because kernel functions responsible for
copying data between kernel and user space failed to verify that a
user-provided address actually resided in the user segment, a local attacker
could issue specially crafted socket function calls to write abritrary values
into kernel memory. By leveraging this capability, it is possible for
unprivileged users to escalate privileges to root.

Vulnerability Details

On Linux, recvmsg() style socket calls are performed using iovec structs, which
allow a user to specify a base address and size for a buffer used to receive
socket data. Each packet family is responsible for defining functions that
copy socket data, which is received by the kernel, back to user space to allow
user programs to process and handle received network data.

When performing this copying of data to user space, the RDS protocol failed to
verify that the base address of a user-provided iovec struct pointed to a valid
userspace address before using the __copy_to_user_inatomic() function to copy
the data. As a result, by providing a kernel address as an iovec base and
issuing a recvmsg() style socket call, a local user could write arbitrary data
into kernel memory. This can be leveraged to escalate privileges to root.

Proof-of-Concept Exploit

VSR has developed a proof-of-concept exploit [4] to both demonstrate the
severity of this issue as well as allow users and administrators to verify the
existence of the vulnerability. The exploit leverages the ability to write
into kernel memory to reset the kernel's security operations structure and gain
root privileges. The exploit requires that kernel symbol resolution is
available to unprivileged users, via /proc/kallsyms or similar, as is the case
on most stock distributions. It has been tested on both 32-bit and 64-bit x86
platforms. While this exploit has been reliable during testing, it is not
advised to run kernel exploits on production systems, as there is a risk of
causing system instability and crashing the affected machine.

Versions Affected

This vulnerability affects unpatched versions of the Linux kernel, starting
from 2.6.30, where the RDS protocol was first included. Installations are only
vulnerable if the CONFIG_RDS kernel configuration option is set, and if there
are no restrictions on unprivileged users loading packet family modules, as is
the case on most stock distributions.

Vendor Response

The following timeline details Linux's response to the reported issue.

2010-10-13 Vulnerability reported to Linux security team
2010-10-13 Response, agreement on disclosure date
2010-10-19 Fix publicly committed [3]
2010-10-19 Coordinated disclosure

Recommendation

Users should either install updates provided by downstream distributions, or
apply the committed patch [3] and recompile their kernel.

Common Vulnerabilities and Exposures (CVE) Information

The Common Vulnerabilities and Exposures (CVE) project has assigned
the number CVE-2010-3904 to this issue. This is a candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.

Acknowledgements

Thanks to Andrew Morton, Linus Torvalds, Andy Grover, and Eugene Teo for their
prompt responses and patch.

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References:

Linux kernel
http://www.linux.org
Reliable Datagram Sockets
http://oss.oracle.com/pipermail/rds-devel/2007-November/000228.html
GIT patch

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=799c10559d60f159ab2232203f222f18fa3c4a5f

RDS protocol privilege escalation exploit
http://www.vsecurity.com/download/tools/linux-rds-exploit.c

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This advisory is distributed for educational purposes only with the sincere
hope that it will help promote public safety. This advisory comes with
absolutely NO WARRANTY; not even the implied warranty of merchantability or
fitness for a particular purpose. Virtual Security Research, LLC nor the author
accepts any liability for any direct, indirect, or consequential loss or damage
arising from use of, or reliance on, this information.

See the VSR disclosure policy for more information on our responsible
disclosure practices: http://www.vsecurity.com/company/disclosure

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