(RHSA-2018:1374) Important: kernel-alt security and bug fix update

The kernel-alt packages provide the Linux kernel version 4.x.

Security Fix(es):

• kernel: ptrace() incorrect error handling leads to corruption and DoS (CVE-2018-1000199)

For more details about the security issue(s), including the impact, a CVSS score, and other related information, refer to the CVE page(s) listed in the References section.

Red Hat would like to thank Andy Lutomirski for reporting this issue.

Bug Fix(es):

• Previously, the nfs_commit_inode() function did not respect the FLUSH_SYNC argument and exited even if there were already the in-flight COMMIT requests. As a consequence, the mmap() system call occasionally returned the EBUSY error on NFS, and CPU soft lockups occurred during a writeback on NFS. This update fixes nfs_commit_inode() to respect FLUSH_SYNC. As a result, mmap() does not return EBUSY, and the CPU soft lockups no longer occur during NFS writebacks. (BZ#1559869)

• Recent IBM z Systems hardware contains an extension to the time-of-day clock that ensures it will be operational after the year 2042 by avoiding an overflow that would happen without it. However, the KVM hypervisor was previously unable to handle the extension correctly, which lead to guests freezing if their kernel supported the time-of-day clock extension. This update adds support for the extension to the KVM hypervisor, and KVM guests which support it no longer freeze. (BZ#1559871)

• This update provides the ability to disable the “RFI Flush” mitigation mechanism for the Meltdown vulnerability (CVE-2017-5754) in the kernel. The patches that mitigate the effect of Meltdown may have negative impact on performance when the mechanism they provide is enabled, and at the same time your systems may not need this mitigation if they are secured by other means. The vulnerability mitigation remains enabled by default and must be disabled manually; this restores system performance to original levels, but the system then also remains vulnerable to Meltdown. Instructions describing how to disable RFI Flush, as well as additional information, is provided in the following Red Hat Knowledgebase article: https://access.redhat.com/articles/3311301 (BZ#1561463)