[Full-Disclosure] [ GLSA 200401-01 ] Linux kernel do_mremap() privelege escalation vulnerability

From: Tim Yamin (plasmaroo_at_gentoo.org)
Date: 01/09/04

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    To: bugtraq@securityfocus.com, full-disclosure@lists.netsys.com, security-alerts@linuxsecurity.com, gentoo-core@gentoo.org, gentoo-announce@gentoo.org
Date: Thu, 08 Jan 2004 23:50:58 +0000

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    Gentoo Linux Security Advisory GLSA 200401-01
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    ~ http://security.gentoo.org
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    ~ Severity: High
    ~ Title: Linux kernel do_mremap() privilege escalation vulnerability
    ~ Date: January 08, 2004
    ~ Bugs: #37292, #37317
    ~ ID: 200401-01

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    Synopsis
    ========

    A critical security vulnerability has been found in recent Linux kernels
    which allows for local privilege escalation.

    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-r2...................YES..........
    ~ arm-sources...............2.4.19-r2................................
    ~ ck-sources................2.4.23-r1...................YES..........
    ~ compaq-sources............2.4.9.32.7-r1............................
    ~ development-sources.......2.6.1_rc3................................
    ~ gaming-sources............2.4.20-r7................................
    ~ gentoo-dev-sources........2.6.1_rc3................................
    ~ gentoo-sources............2.4.20-r10...............................
    ~ gentoo-sources............2.4.22-r3................................
    ~ grsec-sources.............2.4.23.1.9.13-r1.........................
    ~ grsec-sources.............2.4.23.2.0_rc4-r1........................
    ~ gs-sources................2.4.23_pre8-r2...........................
    ~ hardened-sources..........2.4.22-r2................................
    ~ hppa-sources..............2.4.23_p4-r2...........................
    ~ ia64-sources..............2.4.22-r2................................
    ~ mips-prepatch-sources.....2.4.24_pre2-r1...........................
    ~ mips-sources..............2.4.23-r2................................
    ~ mm-sources................2.6.1_rc1-r2................YES..........
    ~ openmosix-sources.........2.4.22-r3................................
    ~ pac-sources...............2.4.23-r1................................
    ~ pfeifer-sources...........2.4.21.1_pre4-r1.........................
    ~ planet-ccrma-sources......2.4.21-r4................................
    ~ ppc-development-sources...2.6.1_rc1-r1................YES..........
    ~ ppc-sources...............2.4.23-r1................................
    ~ ppc-sources-benh..........2.4.22-r4................................
    ~ ppc-sources-crypto........2.4.20-r2................................
    ~ ppc-sources-dev...........2.4.22-r1................................
    ~ selinux-sources...........2.4.24...................................
    ~ sparc-dev-sources.........2.6.1_rc2................................
    ~ sparc-sources.............2.4.24...................................
    ~ usermode-sources..........2.4.23-r1................................
    ~ vanilla-prepatch-sources..2.4.25_pre4..............................
    ~ vanilla-sources...........2.4.24...................................
    ~ win4lin-sources...........2.6.0-r1.................................
    ~ wolk-sources..............4.9-r3...................................
    ~ wolk-sources..............4.10_pre7-r2.............................
    ~ xfs-sources...............2.4.23-r1................................

    ~ 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
    possesses.

    A typical virtual memory area covers at least one memory page. An
    incorrect bound check discovered inside the do_mremap() kernel code
    performing remapping of a virtual memory area may lead to creation of a
    virtual memory area of 0 bytes length.

    The problem is based on the general mremap flaw that remapping 2 pages
    from inside a VMA creates a memory hole of only one page in length but
    an additional VMA of two pages. In the case of a zero sized remapping
    request no VMA hole is created but an additional VMA descriptor of 0
    bytes in length is created.

    This advisory also addresses an information leak in the Linux RTC system.

    Impact
    ======

    Arbitrary code 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() system call
    any process may misuse its unexpected behavior to disrupt the kernel
    memory management subsystem. Proper exploitation of this vulnerability
    may lead to local privilege escalation including execution of arbitrary
    code with kernel level access.

    Proof-of-concept exploit code [ 1 ] 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
    ==========

    There is no temporary workaround - a kernel upgrade is required. A list
    of unaffected kernels is provided along with this announcement.

    Resolution
    ==========

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

    ~ $> emerge sync
    ~ $> emerge -pv your-favorite-sources

    ~ $> # IMPORTANT: IF YOUR KERNEL IS MARKED AS "Manual Update" THEN
    ~ $> # THE PORTAGE MAY REPORT THAT YOU HAVE THE SAME KERNEL ON
    ~ $> # YOUR SYSTEM. YOU SHOULD STILL UPDATE YOUR KERNEL!

    ~ $> emerge your-favorite-sources

    ~ $> # Follow usual procedures for compiling and installing a kernel.
    ~ $> # If you use genkernel, run genkernel as you would do normally.

    ~ $> # See http://www.gentoo.org/doc/en/handbook/handbook.xml for help.

    References
    ==========

    ~ [ 1 ] : http://isec.pl/vulnerabilities/isec-0012-mremap.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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