RHSA-2016:0024 - Security Advisory

Topic

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.

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.

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

Affected Products

• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.6 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.6 i386
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 6.6 s390x
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 6.6 ppc64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.6 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.6 i386
• Red Hat Enterprise Linux EUS Compute Node 6.6 x86_64
• Red Hat Enterprise Linux Server - AUS 6.6 x86_64
• Red Hat Enterprise Linux Server - TUS 6.6 x86_64

Fixes

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

CVEs

• CVE-2015-5307
• CVE-2015-8104

References

• https://access.redhat.com/security/updates/classification/#important