RHSA-2015:2636 - Security Advisory

Topic

Updated kernel packages that fix multiple security issues and several bugs
are now available for Red Hat Enterprise Linux 6.

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.

• A flaw was found in the way the Linux kernel's file system implementation

handled rename operations in which the source was inside and the
destination was outside of a bind mount. A privileged user inside a
container could use this flaw to escape the bind mount and, potentially,
escalate their privileges on the system. (CVE-2015-2925, Important)

• 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)

• A race condition flaw was found in the way the Linux kernel's IPC

subsystem initialized certain fields in an IPC object structure that were
later used for permission checking before inserting the object into a
globally visible list. A local, unprivileged user could potentially use
this flaw to elevate their privileges on the system. (CVE-2015-7613,
Important)

• It was found that the Linux kernel's keys subsystem did not correctly

garbage collect uninstantiated keyrings. A local attacker could use this
flaw to crash the system or, potentially, escalate their privileges on
the system. (CVE-2015-7872, 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:

• Previously, Human Interface Device (HID) ran 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#1268203)

• The NFS client was previously failing to detect a directory loop for some

NFS server directory structures. This failure could cause NFS inodes to
remain referenced after attempting to unmount the file system, leading to a
kernel crash. Loop checks have been added to VFS, which effectively
prevents this problem from occurring. (BZ#1272858)

• Due to a race whereby the nfs_wb_pages_cancel() and

nfs_commit_release_pages() calls both removed a request from the nfs_inode
struct type, the kernel panicked with negative nfs_inode.npages count.
The provided upstream patch performs the required serialization by holding
the inode i_lock over the check of PagePrivate and locking the request,
thus preventing the race and kernel panic from occurring. (BZ#1273721)

• Due to incorrect URB_ISO_ASAP semantics, playing an audio file using a

USB sound card could previously fail for some hardware configurations.
This update fixes the bug, and playing audio from a USB sound card now
works as expected. (BZ#1273916)

• 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.
This update fixes the problem by introducing a required spinlock to the
region tracking functions for proper serialization. The problem only
affects software using huge pages through hugetlb interface. (BZ#1274599)

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 Server 6 x86_64
• Red Hat Enterprise Linux Server 6 i386
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.7 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.7 i386
• Red Hat Enterprise Linux Server - Extended Life Cycle Support 6 x86_64
• Red Hat Enterprise Linux Workstation 6 x86_64
• Red Hat Enterprise Linux Workstation 6 i386
• Red Hat Enterprise Linux Desktop 6 x86_64
• Red Hat Enterprise Linux Desktop 6 i386
• Red Hat Enterprise Linux for IBM z Systems 6 s390x
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 6.7 s390x
• Red Hat Enterprise Linux for Power, big endian 6 ppc64
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 6.7 ppc64
• Red Hat Enterprise Linux for Scientific Computing 6 x86_64
• Red Hat Enterprise Linux Server from RHUI 6 x86_64
• Red Hat Enterprise Linux Server from RHUI 6 i386
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.7 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.7 i386
• Red Hat Enterprise Linux Server - Extended Life Cycle Support 6 i386
• Red Hat Enterprise Linux EUS Compute Node 6.7 x86_64
• Red Hat Enterprise Linux for SAP Solutions for x86_64 - Extended Update Support 6.7 x86_64
• Red Hat Enterprise Linux Server - Extended Life Cycle Support (for IBM z Systems) 6 s390x

Fixes

• BZ - 1209367 - CVE-2015-2925 Kernel: vfs: Do not allow escaping from bind mounts
• BZ - 1268270 - CVE-2015-7613 kernel: Unauthorized access to IPC objects with SysV shm
• BZ - 1272371 - CVE-2015-7872 kernel: Keyrings crash triggerable by unprivileged user
• 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-2015-2925
• CVE-2015-7613
• CVE-2015-5307
• CVE-2015-8104
• CVE-2015-7872

References

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