(RHSA-2009:1239) Important: kernel-rt security and bug fix update

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

These updated packages fix the following security issues:

• Tavis Ormandy and Julien Tinnes of the Google Security Team reported a
  flaw in the SOCKOPS_WRAP macro in the Linux kernel. This macro did not
  initialize the sendpage operation in the proto_ops structure correctly. A
  local, unprivileged user could use this flaw to cause a local denial of
  service or escalate their privileges. (CVE-2009-2692, Important)

• 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:

• 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#511187)

• a bug in the locking strategy for the free_pages_bulk() kernel function
  was found, where a lock in a code branch was not held. This could have
  created a “double free” problem that resulted in a kernel panic.
  (BZ#513715)

• udevd and multipathd were unable to service events fast enough when a
  Fibre Channel cable was unplugged. This caused the cable state to be out of
  sync if the cable was plugged back in quickly, possibly resulting in
  devices being removed, or path issues when using Device-Mapper Multipath.
  This has been changed so that users can specify devices that should not be
  removed if a cable is unplugged. (BZ#514541)

• a race condition in exit_thread() could have eventually caused a kernel
  oops. (BZ#514587)

• a race condition was fixed between kthread_stop() and kthread_create().
  Kernel subsystems creating and stopping threads at a fast pace could hit
  this issue. Several inexplicable backtraces observed during tests
  caused this race condition. (BZ#518967)

• HPET_EMULATE_RTC was being disabled during kernel compile. This was
  caused by an incorrect requirement in the related Kconfig entry. This issue
  led to failures when accessing the RTC (real time clock) in machines that
  had the RTC emulated by HPET (High Precision Event Timer). (BZ#519433)

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.