(RHSA-2017:3295) Moderate: 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.

Security Fix(es):

• It was found that the timer functionality in the Linux kernel ALSA subsystem is prone to a race condition between read and ioctl system call handlers, resulting in an uninitialized memory disclosure to user space. A local user could use this flaw to read information belonging to other users. (CVE-2017-1000380, Moderate)

Red Hat would like to thank Alexander Potapenko (Google) for reporting this issue.

Bug Fix(es):

• The current realtime throttling mechanism prevents the starvation of non-realtime tasks by CPU-intensive realtime tasks. When a realtime run queue is throttled, it allows non-realtime tasks to run. If there are not non-realtime tasks, the CPU goes idle. To safely maximize CPU usage by decreasing the CPU idle time, the RT_RUNTIME_GREED scheduler feature has been implemented. When enabled, this feature checks if non-realtime tasks are starving before throttling the realtime task. The RT_RUNTIME_GREED scheduler option guarantees some run time on all CPUs for the non-realtime tasks, while keeping the realtime tasks running as much as possible. (BZ#1459275)

• The kernel-rt packages have been upgraded to version 3.10.0-693.11.1.rt56.595, which provides a number of security and bug fixes over the previous version. (BZ#1500036)

• In the realtime kernel, if the rt_mutex locking mechanism was taken in the interrupt context, the normal priority inheritance protocol incorrectly identified a deadlock, and a kernel panic occurred. This update reverts the patch that added rt_mutex in the interrupt context, and the kernel no longer panics due to this behavior. (BZ#1509021)