(RHSA-2009:1466) Important: kernel security and bug fix update

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.