(RHSA-2012:0720) Important: kernel security and bug fix update

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

This update fixes the following security issues:

• It was found that the Xen hypervisor implementation as shipped with Red
  Hat Enterprise Linux 5 did not properly restrict the syscall return
  addresses in the sysret return path to canonical addresses. An
  unprivileged user in a 64-bit para-virtualized guest, that is running on a
  64-bit host that has an Intel CPU, could use this flaw to crash the host
  or, potentially, escalate their privileges, allowing them to execute
  arbitrary code at the hypervisor level. (CVE-2012-0217, Important)

Note: For Red Hat Enterprise Linux guests, only privileged guest users can
exploit CVE-2012-0217.

• A flaw in the xfrm6_tunnel_rcv() function in the Linux kernel’s IPv6
  implementation could lead to a use-after-free or double free flaw in
  tunnel6_rcv(). A remote attacker could use this flaw to send
  specially-crafted packets to a target system that is using IPv6 and also
  has the xfrm6_tunnel kernel module loaded, causing it to crash.
  (CVE-2012-1583, Important)

If you do not run applications that use xfrm6_tunnel, you can prevent the
xfrm6_tunnel module from being loaded by creating (as the root user) a
“/etc/modprobe.d/xfrm6_tunnel.conf” file, and adding the following line to
it:

blacklist xfrm6_tunnel

This way, the xfrm6_tunnel module cannot be loaded accidentally. A reboot
is not necessary for this change to take effect.

Red Hat would like to thank the Xen project for reporting CVE-2012-0217.
Upstream acknowledges Rafal Wojtczuk as the original reporter of
CVE-2012-0217.

This update also fixes the following bugs:

• A bug in the vsyscall interface caused 32-bit multi-threaded programs,
  which received the SIGCANCEL signal right after they returned from a system
  call, to terminate unexpectedly with a segmentation fault when run on the
  AMD64 or Intel 64 architecture. A patch has been provided to address this
  issue and the crashes no longer occur in the described scenario.
  (BZ#807929)

• Incorrect duplicate MAC addresses were being used on a rack network
  daughter card that contained a quad-port Intel I350 Gigabit Ethernet
  Controller. With this update, the underlying source code has been modified
  to address this issue, and correct MAC addresses are now used under all
  circumstances. (BZ#813195)

• When the Fibre Channel (FC) layer sets a device to “running”, the layer
  also scans for other new devices. Previously, there was a race condition
  between these two operations. Consequently, for certain targets, thousands
  of invalid devices were created by the SCSI layer and the udev service.
  This update ensures that the FC layer always sets a device to “online”
  before scanning for others, thus fixing this bug.

Additionally, when attempting to transition priority groups on a busy FC
device, the multipath layer retried immediately. If this was the only
available path, a large number of retry operations were performed in a
short period of time. Consequently, the logging of retry messages slowed
down the system. This bug has been fixed by ensuring that the DM Multipath
feature delays retry operations in the described scenario. (BZ#816683)

• Due to incorrect use of the list_for_each_entry_safe() macro, the
  enumeration of remote procedure calls (RPCs) priority wait queue tasks
  stored in the tk_wait.links list failed. As a consequence, the
  rpc_wake_up() and rpc_wake_up_status() functions failed to wake up all
  tasks. This caused the system to become unresponsive and could
  significantly decrease system performance. Now, the
  list_for_each_entry_safe() macro is no longer used in rpc_wake_up(),
  ensuring reasonable system performance. (BZ#817570)

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.