FreeBSD Security Advisory FreeBSD-SA-10:09.pseudofs

Type securityvulns
Reporter Securityvulns
Modified 2010-11-15T00:00:00



============================================================================= FreeBSD-SA-10:09.pseudofs Security Advisory The FreeBSD Project

Topic: Spurious mutex unlock

Category: core Module: pseudofs Announced: 2010-11-10 Credits: Przemyslaw Frasunek Affects: FreeBSD 7.x prior to 7.3-RELEASE, 8.x prior to 8.0-RC1 Corrected: 2009-09-05 13:10:54 UTC (RELENG_8, 8.0-RC1) 2009-09-05 13:31:16 UTC (RELENG_7, 7.2-STABLE) 2010-11-10 23:36:13 UTC (RELENG_7_1, 7.1-RELEASE-p15) CVE Name: CVE-2010-4210

For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:>.

I. Background

pseudofs offers an abstract API for pseudo file systems which is utilized by procfs(5) and linprocfs(5). It provides generic file system services such as ACLs, extended attributes which interface with VFS and which are otherwise onerous to implement. This enables pseudo file system authors to add this functionality to their file systems with minimal effort.

II. Problem Description

The pfs_getextattr(9) function, used by pseudofs for handling extended attributes, attempts to unlock a mutex which was not previously locked.

III. Impact

On systems where a pseudofs-using filesystem is mounted and NULL page mapping is allowed, an attacker can overwrite arbitrary memory locations in the kernel with zero, and in certain cases execute arbitrary code in the context of the kernel.

On systems which do not allow NULL page mapping, an attacker can cause the FreeBSD kernel to panic.

IV. Workaround

Exploiting this vulnerability requires that the adversary can open a file on a file system which uses pseudofs. This includes procfs(5) or linprocfs(5). Un-mounting these file systems will mitigate the risk associated with this vulnerability.

Providing that the patch associated with the FreeBSD-EN-09:05.null errata notice has been applied, setting the security.bsd.map_at_zero sysctl to 0 will prevent arbitrary code execution (but a kernel panic will still be possible).

V. Solution

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE, or to the RELENG_7_1 security branch dated after the correction date.

2) To update your vulnerable system via a source code patch:

The following patch has been verified to apply to FreeBSD 7.1 systems.

a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility.



b) Apply the patch.

cd /usr/src

patch < /path/to/patch

c) Recompile your kernel as described in <URL:> and reboot the system.

3) To update your vulnerable system via a binary patch:

Systems running 7.1-RELEASE on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility:

freebsd-update fetch

freebsd-update install

VI. Correction details

The following list contains the revision numbers of each file that was corrected in FreeBSD.


Branch Revision Path

RELENG_7 src/sys/fs/pseudofs/pseudofs_vnops.c RELENG_7_1 src/UPDATING 1.507. src/sys/conf/ src/sys/fs/pseudofs/pseudofs_vnops.c RELENG_8 src/sys/fs/pseudofs/pseudofs_vnops.c


Branch/path Revision

stable/7/ r196860 releng/7.1/ r205103 stable/8/ r196859

VII. References

The latest revision of this advisory is available at -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (FreeBSD)

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