RHSA-2018:2790: 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 tcpcollapseofoqueue() and tcppruneofoqueue() 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, 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#1618386)