4.9 - RHSA-2016:0024

Problem Description:

Updated kernel packages that fix two security issues and several bugs are now available for Red Hat Enterprise Linux 6.6 Extended Update Support.

Red Hat Product Security has rated this update as having Important security impact. Common Vulnerability Scoring System (CVSS) base scores, which give detailed severity ratings, are available for each vulnerability from the CVE links in the References section.

2. Relevant releases/architectures:

Red Hat Enterprise Linux Compute Node Optional EUS (v. 6.6) - x86_64 Red Hat Enterprise Linux HPC Node EUS (v. 6.6) - noarch, x86_64 Red Hat Enterprise Linux Server EUS (v. 6.6) - i386, noarch, ppc64, s390x, x86_64 Red Hat Enterprise Linux Server Optional EUS (v. 6.6) - i386, ppc64, s390x, x86_64

3. Description:

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

* It was found that the x86 ISA (Instruction Set Architecture) is prone to a denial of service attack inside a virtualized environment in the form of an infinite loop in the microcode due to the way (sequential) delivering of benign exceptions such as #AC (alignment check exception) and #DB (debug exception) is handled. A privileged user inside a guest could use these flaws to create denial of service conditions on the host kernel. (CVE-2015-5307, CVE-2015-8104, Important)

Red Hat would like to thank Ben Serebrin of Google Inc. for reporting the CVE-2015-5307 issue.

This update also fixes the following bugs:

* When doing TSO/GSO in the presence of VLAN headers on a macvtap device, the header offsets were incorrectly calculated. As a consequence, when 2 guests on the same host communicated over a guest configured VLAN, performance dropped to about 1 Mbps. A set of patches has been provided to fix this bug, and network performance with VLAN tags now works with optimal performance. (BZ#1215914)

* Prior to this update, TSO acceleration features have been removed from the VLAN device which caused that VLAN performance on top of a virtio device was much lower than that of a virtio device itself. This update re-enables TSO acceleration features, and performance of VLAN devices on top of a virtio device has thus been restored. (BZ#1240988)

* With an IPv6 address on a bond and a slave failover, Unsolicited Neighbor Advertisement (UNA) was previously sent using the link global IPv6 address as source address. The underlying source code has been patched, and, after the failover in bonding, UNA is sent using both the corresponding link IPv6 address and global IPv6 address of bond0 and bond0.vlan. (BZ#1258480)

* Previously, Human Interface Device (HID) would run a report on an unaligned buffer, which could cause a page fault interrupt and an oops when the end of the report was read. This update fixes this bug by padding the end of the report with extra bytes, so the reading of the report never crosses a page boundary. As a result, a page fault and subsequent oops no longer occur. (BZ#1268202)

* Inside hugetlb, region data structures were protected by a combination of a memory map semaphore and a single hugetlb instance mutex. However, a page-fault scalability improvement backported to the kernel on previous releases removed the single hugetlb instance mutex and introduced a new mutex table, making the locking combination insufficient, leading to possible race windows that could cause corruption and undefined behavior. The problem could be seen for example with software mapping or re-mapping hugetlb areas with concurrent threads reading/writing to same areas causing page faults. This update fixes the problem by introducing now a required spinlock to the region tracking functions for proper serialization. The problem only affects software using huge pages through hugetlb interface. (BZ#1274597)

* Previously, VLAN stacked on the macvlan or macvtap device did not work for devices that implement and use VLAN filters. As a consequence, macvtap passthrough mode failed to transfer VLAN packets over the be2net driver. This update implements VLAN ndo calls to the macvlan driver to pass appropriate VLAN tag IDs to lower devices. As a result, macvtap transfers VLAN packets over be2net successfully. (BZ#1280205)

All kernel users are advised to upgrade to these updated packages, which contain backported patches to correct these issues. The system must be rebooted for this update to take effect.

4. Solution:

Before applying this update, make sure all previously released errata relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258

5. Bugs fixed (https://bugzilla.redhat.com/):

1277172 - CVE-2015-5307 virt: guest to host DoS by triggering an infinite loop in microcode via #AC exception 1278496 - CVE-2015-8104 virt: guest to host DoS by triggering an infinite loop in microcode via #DB exception