(Gentoo Issues Fix) Linux Kernel do_mremap() Fails to Check do_munmap() Return Values, Allowing a Local User to Gain Root Privileges


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Gentoo Linux Security Advisory                           GLSA 200403-02
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~                                            http://security.gentoo.org
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~  Severity: High
~     Title: Linux kernel do_mremap local privilege escalation
~            vulnerability
~      Date: March 06, 2004
~      Bugs: #42024
~        ID: 200403-02

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Synopsis
========

A critical security vulnerability has been found in recent Linux
kernels by Paul Starzetz of iSEC Security Research which allows for
local privilege escalations.

Background
==========

The Linux kernel is responsible for memory management in a working
system - to allow this, processes are allowed to allocate and
unallocate memory.

Affected packages
=================

~   -------------------------------------------------------------------
~          Kernel      /   Unaffected Version   /    Manual Update?
~   -------------------------------------------------------------------

~   aa-sources................2.4.23-r1...................YES..........
~   alpha-sources.............2.4.21-r4................................
~   ck-sources................2.4.24-r1...................YES..........
~   ck-sources................2.6.2-r1....................YES..........
~   compaq-sources............2.4.9.32.7-r2............................
~   development-sources.......2.6.3_rc1................................
~   gaming-sources............2.4.20-r8................................
~   gentoo-dev-sources........2.6.3_rc1................................
~   gentoo-sources............2.4.19-r11...............................
~   gentoo-sources............2.4.20-r12...............................
~   gentoo-sources............2.4.22-r7................................
~   grsec-sources.............2.4.24.1.9.13-r1.........................
~   gs-sources................2.4.25_pre7-r2...........................
~   hardened-sources..........2.4.24-r1................................
~   hppa-dev-sources..........2.6.2_p3-r1..............................
~   hppa-sources..............2.4.24_p0-r1.............................
~   ia64-sources..............2.4.24-r1................................
~   mips-prepatch-sources.....2.4.25_pre6-r1...........................
~   mips-sources..............2.4.25_rc4...............................
~   mm-sources................2.6.3_rc1-r1.............................
~   openmosix-sources.........2.4.22-r4................................
~   pac-sources...............2.4.23-r3................................
~   planet-ccrma-sources......2.4.21-r5................................
~   ppc-development-sources...2.6.3_rc1-r1.............................
~   ppc-sources...............2.4.24-r1................................
~   ppc-sources-benh..........2.4.22-r5................................
~   ppc-sources-crypto........2.4.20-r3................................
~   ppc-sources-dev...........2.4.24-r2................................
~   selinux-sources...........2.4.24-r2................................
~   sparc-dev-sources.........2.6.3_rc1................................
~   sparc-sources.............2.4.24-r2................................
~   usermode-sources..........2.4.24-r1................................
~   usermode-sources..........2.6.3-r1.................................
~   vanilla-prepatch-sources..2.4.25_rc4...............................
~   vanilla-sources...........2.4.25...................................
~   win4lin-sources...........2.4.23-r2................................
~   win4lin-sources...........2.6.2-r1.................................
~   wolk-sources..............4.9-r4...................................
~   wolk-sources..............4.10_pre7-r3.............................
~   xfs-sources...............2.4.24-r2................................

~   IMPORTANT: IF YOUR KERNEL IS MARKED AS "YES" ABOVE, THEN YOU SHOULD
~              UPDATE YOUR KERNEL EVEN IF PORTAGE REPORTS THAT THE SAME
~              VERSION IS INSTALLED.

Description
===========

The memory subsystem allows for shrinking, growing, and moving of
chunks of memory along any of the allocated memory areas which the
kernel posesses.

To accomplish this, the do_mremap code calls the do_munmap() kernel
function to remove any old memory mappings in the new location - but,
the code doesn't check the return value of the do_munmap() function
which may fail if the maximum number of available virtual memory area
descriptors has been exceeded.

Due to the missing return value check after trying to unmap the middle
of the first memory area, the corresponding page table entries from
the second new area are inserted into the page table locations
described by the first old one, thus they are subject to page
protection flags of the first area. As a result, arbitrary code can be
executed.

Impact
======

Arbitrary code with normal non-superuser privelerges may be able to
exploit this vulnerability and may disrupt the operation of other
parts of the kernel memory management subroutines finally leading to
unexpected behavior.

Since no special privileges are required to use the mremap() and
mummap() system calls any process may misuse this unexpected behavior
to disrupt the kernel memory management subsystem. Proper exploitation
of this vulnerability may lead to local privilege escalation allowing
for the execution of arbitrary code with kernel level root access.

Proof-of-concept exploit code has been created and successfully
tested, permitting root escalation on vulnerable systems. As a result,
all users should upgrade their kernels to new or patched versions.

Workaround
==========

Users who are unable to upgrade their kernels may attempt to use "sysctl
- -w vm.max_map_count=1000000", however, this is a temporary fix which
only solves the problem by increasing the number of memory areas that
can be created by each process. Because of the static nature of this
workaround, it is not recommended and users are urged to upgrade their
systems to the latest avaiable patched sources.

Resolution
==========

Users are encouraged to upgrade to the latest available sources for
their system:

~    # emerge sync
~    # emerge -pv your-favourite-sources
~    # emerge your-favourite-sources
~    # # Follow usual procedure for compiling and installing a kernel.
~    # # If you use genkernel, run genkernel as you would do normally.

~    # # IF YOUR KERNEL IS MARKED as "remerge required!" THEN
~    # # YOU SHOULD UPDATE YOUR KERNEL EVEN IF PORTAGE
~    # # REPORTS THAT THE SAME VERSION IS INSTALLED.

References
==========

~  [ 1 ] http://isec.pl/vulnerabilities/isec-0014-mremap-unmap.txt

Concerns?
=========

Security is a primary focus of Gentoo Linux and ensuring the
confidentiality and security of our users machines is of utmost
importance to us. Any security concerns should be addressed to
security@gentoo.org or alternatively, you may file a bug at
http://bugs.gentoo.org.

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