Red Hat 6.4 RHSA-2015:1643-01 Moderate: Kernel Escalation Risk Fix

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 To fix this bug, the BUG_ON() function has been replaced by WARN_ON(), which prevents the kernel from panicking in the aforementioned situation.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.