(RHSA-2015:1643) Moderate: kernel security and bug fix update

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

• It was found that the Linux kernel’s ping socket implementation did not
  properly handle socket unhashing during spurious disconnects, which could
  lead to a use-after-free flaw. On x86-64 architecture systems, a local user
  able to create ping sockets could use this flaw to crash the system.
  On non-x86-64 architecture systems, a local user able to create ping
  sockets could use this flaw to escalate their privileges on the system.
  (CVE-2015-3636, Moderate)

This update also fixes the following bugs:

• Due to bad memory or memory corruption, an isolated BUG_ON(mm->nr_ptes)
  was sometimes reported, indicating that not all the page tables allocated
  could be found and freed when the exit_mmap() function cleared the user
  address space. As a consequence, a kernel panic occurred. To fix this bug,
  the BUG_ON() function has been replaced by WARN_ON(), which prevents the
  kernel from panicking in the aforementioned situation. (BZ#1235929)

• Previously, it was for the ext4 driver to read a metadata block and use
  it without a verification. If the metadata block was corrupted, a kernel
  panic could occur. With this update, verification is forced on every buffer
  before it is used, which uncovers possible corruption and prevents further
  use of the corrupted metadata buffer. (BZ#1242930)

All kernel users are advised to upgrade to these updated packages, which
contain backported patches to correct these issues. The system must be
rebooted for this update to take effect.