Important: kernel security and bug fix update

Updated kernel packages that fix two security issues and several bugs are
now available for Red Hat Enterprise Linux 5.3 Extended Update Support.

This update has been rated as having important security impact by the Red
Hat Security Response Team.

The kernel packages contain the Linux kernel, the core of any Linux
operating system.

This update includes backported fixes for two security issues. These issues
only affected users of Red Hat Enterprise Linux 5.3 Extended Update Support
as they have already been addressed for users of Red Hat Enterprise Linux 5
in the 5.4 update, RHSA-2009:1243.

In accordance with the support policy, future security updates to Red Hat
Enterprise Linux 5.3 Extended Update Support will only include issues of
critical security impact.

This update fixes the following security issues:

* it was discovered that, when executing a new process, the clear_child_tid
pointer in the Linux kernel is not cleared. If this pointer points to a
writable portion of the memory of the new program, the kernel could corrupt
four bytes of memory, possibly leading to a local denial of service or
privilege escalation. (CVE-2009-2848, Important)

* a flaw was found in the way the do_sigaltstack() function in the Linux
kernel copies the stack_t structure to user-space. On 64-bit machines, this
flaw could lead to a four-byte information leak. (CVE-2009-2847, Moderate)

This update also fixes the following bugs:

* a regression was found in the SCSI retry logic: SCSI mode select was not
retried when retryable errors were encountered. In Device-Mapper Multipath
environments, this could cause paths to fail, or possibly prevent
successful failover. (BZ#506905)

* the gcc flag "-fno-delete-null-pointer-checks" was added to the kernel
build options. This prevents gcc from optimizing out NULL pointer checks
after the first use of a pointer. NULL pointer bugs are often exploited by
attackers, and keeping these checks is considered a safety measure.
(BZ#515468)

* due to incorrect APIC timer calibration, a system hang could have
occurred while booting certain systems. This incorrect timer calibration
could have also caused the system time to become faster or slower. With
this update, it is still possible for APIC timer calibration issues to
occur; however, a clear warning is now provided if they do. (BZ#521237)

* gettimeofday() experienced poor performance (which caused performance
problems for applications using gettimeofday()) when running on hypervisors
that use hardware assisted virtualization. With this update, MFENCE/LFENCE
is used instead of CPUID for gettimeofday() serialization, which resolves
this issue. (BZ#523280)

Users should upgrade to these updated packages, which contain backported
patches to correct these issues. The system must be rebooted for this
update to take effect.

Before applying this update, make sure that all previously-released
errata relevant to your system have been applied.

This update is available via Red Hat Network. Details on how to use
the Red Hat Network to apply this update are available at
http://kbase.redhat.com/faq/docs/DOC-11259

506905 - LTC 49790: Sync up SCSI DH code with mainline changes [rhel-5.3.z]
515392 - CVE-2009-2847 kernel: information leak in sigaltstack
515423 - CVE-2009-2848 kernel: execve: must clear current->clear_child_tid
515468 - kernel: build with -fno-delete-null-pointer-checks [rhel-5.3.z]
521237 - [RHEL 5] Hang on boot due to wrong APIC timer calibration [rhel-5.3.z]
523280 - RFE: improve gettimeofday performance on hypervisors [rhel-5.3.z]

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-2847
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-2848
http://www.redhat.com/security/updates/classification/#important