Synopsis

Important: kernel-rt security and bug fix update

Type/Severity

Security Advisory: Important

Topic

An update for kernel-rt is now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

Description

The kernel-rt packages provide the Real Time Linux Kernel, which enables fine-tuning for systems with extremely high determinism requirements.

Security Fix(es):

• A use-after-free vulnerability was found in the kernel's socket recvmmsg subsystem. This may allow remote attackers to corrupt memory and may allow execution of arbitrary code. This corruption takes place during the error handling routines within __sys_recvmmsg() function. (CVE-2016-7117, Important)
• A use-after-free vulnerability was found in tcp_xmit_retransmit_queue and other tcp_* functions. This condition could allow an attacker to send an incorrect selective acknowledgment to existing connections, possibly resetting a connection. (CVE-2016-6828, Moderate)
• A flaw was found in the Linux kernel's implementation of sctp protocol in which a remote attacker can trigger an out of bounds read with an offset of up to 64kB. This may panic the machine with a page-fault. (CVE-2016-9555, Moderate)

Bug Fix(es):

• The kernel-rt packages have been upgraded to the 3.10.0-514.6.1 source tree, which provides a number of bug fixes over the previous version. (BZ#1401863)
• Previously, the device mapper (DM) subsystem was not notified that the real-time kernel changes the way preemption works with spinlocks. This caused a kernel panic when the dm-multipath kernel module was loaded because the interrupt request (IRQ) check was invalid on the real-time kernel. This check has been corrected enabling the system to boot correctly with the dm-multipath module enabled. (BZ#1400930)
• Unlike the standard Linux kernel, the real-time kernel does not disable interrupts inside the Interrupt Service Routines driver. Because of this difference, a New API (NAPI) function for turning interrupt requests (IRQ) off was actually being called with IRQs enabled. Consequently, the NAPI poll list was being corrupted, causing improper networking card operation and potential kernel hangs. With this update, the NAPI function has been corrected to force modifications of the poll list to be protected allowing proper operation of the networking card drivers. (BZ#1402837)

Solution

For details on how to apply this update, which includes the changes described in this advisory, refer to:

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

The system must be rebooted for this update to take effect.

Affected Products

• Red Hat Enterprise Linux for Real Time 7 x86_64
• Red Hat Enterprise Linux for Real Time for NFV 7 x86_64

Fixes

• BZ - 1367091 - CVE-2016-6828 kernel: Use after free in tcp_xmit_retransmit_queue
• BZ - 1382268 - CVE-2016-7117 kernel: Use-after-free in the recvmmsg exit path
• BZ - 1397930 - CVE-2016-9555 kernel: Slab out-of-bounds access in sctp_sf_ootb()
• BZ - 1400930 - RT kernel panics with dm-multipath enabled
• BZ - 1401863 - kernel-rt: update to the RHEL7.3.z batch#2 source tree

CVEs

• CVE-2016-6828
• CVE-2016-7117
• CVE-2016-9555

References