RHSA-2016:0024: Important: kernel security and bug fix update

The kernel packages contain the Linux kernel, the core of any Linuxoperating 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 ofan infinite loop in the microcode due to the way (sequential) delivering ofbenign exceptions such as #AC (alignment check exception) and #DB (debugexception) is handled. A privileged user inside a guest could use theseflaws 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 theCVE-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 2guests on the same host communicated over a guest configured VLAN,performance dropped to about 1 Mbps. A set of patches has been provided tofix this bug, and network performance with VLAN tags now works with optimalperformance. (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 virtiodevice was much lower than that of a virtio device itself. This updatere-enables TSO acceleration features, and performance of VLAN devices ontop 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 addressas source address. The underlying source code has been patched, and, afterthe failover in bonding, UNA is sent using both the corresponding link IPv6address 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 whenthe end of the report was read. This update fixes this bug by padding theend of the report with extra bytes, so the reading of the report nevercrosses a page boundary. As a result, a page fault and subsequent oops nolonger 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, apage-fault scalability improvement backported to the kernel on previousreleases removed the single hugetlb instance mutex and introduced a newmutex table, making the locking combination insufficient, leading topossible race windows that could cause corruption and undefined behavior.The problem could be seen for example with software mapping or re-mappinghugetlb areas with concurrent threads reading/writing to same areas causingpage faults. This update fixes the problem by introducing now a requiredspinlock to the region tracking functions for proper serialization. Theproblem 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, macvtappassthrough mode failed to transfer VLAN packets over the be2net driver.This update implements VLAN ndo calls to the macvlan driver to passappropriate VLAN tag IDs to lower devices. As a result, macvtap transfersVLAN packets over be2net successfully. (BZ#1280205)All kernel users are advised to upgrade to these updated packages, whichcontain backported patches to correct these issues. The system must berebooted for this update to take effect.