(RHSA-2016:1541) Important: kernel-rt security and bug fix update

The kernel-rt packages provide the Real Time Linux Kernel, which enables fine-tuning for systems with extremely high determinism requirements.

• A flaw was found in the Linux kernel’s keyring handling code, where in key_reject_and_link() an uninitialised variable would eventually lead to arbitrary free address which could allow attacker to use a use-after-free style attack. (CVE-2016-4470, Important)

• The ovl_setattr function in fs/overlayfs/inode.c in the Linux kernel through 4.3.3 attempts to merge distinct setattr operations, which allows local users to bypass intended access restrictions and modify the attributes of arbitrary overlay files via a crafted application. (CVE-2015-8660, Moderate)

Red Hat would like to thank Nathan Williams for reporting CVE-2015-8660. The CVE-2016-4470 issue was discovered by David Howells (Red Hat Inc.).

The kernel-rt packages have been upgraded to the kernel-3.10.0-327.28.2.el7 source tree, which provides a number of bug fixes over the previous version. (BZ#1350307)

This update also fixes the following bugs:

• Previously, use of the get/put_cpu_var() function in function refill_stock() from the memcontrol cgroup code lead to a “scheduling while atomic” warning. With this update, refill_stock() uses the get/put_cpu_light() function instead, and the warnings no longer appear. (BZ#1347171)

• Prior to this update, if a real time task pinned to a given CPU was taking 100% of the CPU time, then calls to the lru_add_drain_all() function on other CPUs blocked for an undetermined amount of time. This caused latencies and undesired side effects. With this update, lru_add_drain_all() has been changed to drain the LRU pagevecs of remote CPUs. (BZ#1348523)