(RHSA-2018:2776) Important: kernel security and bug fix update

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

Security Fix(es):

• A flaw named SegmentSmack was found in the way the Linux kernel handled specially crafted TCP packets. A remote attacker could use this flaw to trigger time and calculation expensive calls to tcp_collapse_ofo_queue() and tcp_prune_ofo_queue() functions by sending specially modified packets within ongoing TCP sessions which could lead to a CPU saturation and hence a denial of service on the system. Maintaining the denial of service condition requires continuous two-way TCP sessions to a reachable open port, thus the attacks cannot be performed using spoofed IP addresses. (CVE-2018-5390)

Red Hat would like to thank Juha-Matti Tilli (Aalto University - Department of Communications and Networking and Nokia Bell Labs) for reporting this issue.

Bug Fix(es):

• Previously, making the total buffer size bigger than the memory size for early allocation through the trace_buf_size boot option, made the system become unresponsive at the boot stage. This update introduces a change in the early memory allocation. As a result, the system no longer hangs in the above described scenario. (BZ#1588365)

• When inserting objects with the same keys, made the rhlist implementation corrupt the chain pointers. As a consequence, elements were missing on removal and traversal. This patch updates the chain pointers correctly. As a result, there are no missing elements on removal and traversal in the above-described scenario. (BZ#1601008)

• Previously, the kernel source code was missing support to report the Speculative Store Bypass Disable (SSBD) vulnerability status on IBM Power Systems and the little-endian variants of IBM Power Systems. As a consequence, the /sys/devices/system/cpu/vulnerabilities/spec_store_bypass file incorrectly reported “Not affected” on both CPU architectures. This fix updates the kernel source code to properly report the SSBD status either as “Vulnerable” or “Mitigation: Kernel entry/exit barrier (TYPE)” where TYPE is one of “eieio”, “hwsync”, “fallback”, or “unknown”. (BZ#1612352)

• Previously, the early microcode updater in the kernel was trying to perform a microcode update on virtualized guests. As a consequence, the virtualized guests sometimes mishandled the request to perform the microcode update and became unresponsive in the early boot stage. This update applies an upstream patch to avoid the early microcode update when running under a hypervisor. As a result, no kernel freezes appear in the described scenario. (BZ#1618389)