Red Hat EUS 5.6 RHSA-2012:1087-01 Critical: Kernel Flaw

The kernel packages contain the Linux kernel, the core of any Linux operating system.
This update fixes the following security issue:
* It was found that the data_len parameter of the sock_alloc_send_pskb() function in the Linux kernel's networking implementation was not validated before use. A local user with access to a TUN/TAP virtual interface could use this flaw to crash the system or, potentially, escalate their privileges. Note that unprivileged users cannot access TUN/TAP devices until the root user grants them access. (CVE-2012-2136, Important)
This update also fixes the following bugs:
* An insufficiently designed calculation in the CPU accelerator in the previous kernel caused an arithmetic overflow in the sched_clock() function when system uptime exceeded 208.5 days. This overflow led to a kernel panic on the systems using the Time Stamp Counter (TSC) or Virtual Machine Interface (VMI) clock source. This update corrects the described calculation so that this arithmetic overflow and kernel panic can no longer occur under these circumstances. (BZ#825981, BZ#835449)
* Previously, a race condition between the journal_write_metadata_buffer() and jbd_unlock_bh_state() functions could occur. Consequently, another thread could call the get_write_access() function on the buffer head and cause the wrong data to be written into the journal. If the system terminated unexpectedly or was shut down incorrectly, subsequent file system journal replay could result in file system corruption. This update fixes the race condition and the file system corruption no longer occurs in the described scenario. (BZ#833764)
* When the kvmclock initialization was used in a guest, it could write to the Time Stamp Counter (TSC) and, under certain circumstances, could cause the kernel to become unresponsive on boot. With this update, TSC synchronization, which is unnecessary due to kvmclock, has been disabled, thus fixing this bug. (BZ#834557)
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.