Synopsis

Important: kernel security and bug fix update

Type/Severity

Security Advisory: Important

Topic

An update for kernel is now available for Red Hat Enterprise Linux 6.6 Advanced Update Support and Red Hat Enterprise Linux 6.6 Telco Extended Update Support.

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

Security Fix(es):

• A flaw was found in the way memory was being allocated on the stack for user space binaries. If heap (or different memory region) and stack memory regions were adjacent to each other, an attacker could use this flaw to jump over the stack guard gap, cause controlled memory corruption on process stack or the adjacent memory region, and thus increase their privileges on the system. This is a kernel-side mitigation which increases the stack guard gap size from one page to 1 MiB to make successful exploitation of this issue more difficult. (CVE-2017-1000364, Important)
• A race condition flaw was found in the N_HLDC Linux kernel driver when accessing n_hdlc.tbuf list that can lead to double free. A local, unprivileged user able to set the HDLC line discipline on the tty device could use this flaw to increase their privileges on the system. (CVE-2017-2636, Important)

Red Hat would like to thank Qualys Research Labs for reporting CVE-2017-1000364 and Alexander Popov for reporting CVE-2017-2636.

Bug Fix(es):

• Previously, the kdump mechanism was trying to get the lock by the vmalloc_sync_all() function during a kernel panic. Consequently, a deadlock occurred, and the crashkernel did not boot. This update fixes the vmalloc_sync_all() function to avoid synchronizing the vmalloc area on the crashing CPU. As a result, the crashkernel parameter now boots as expected, and the kernel dump is collected successfully under the described circumstances. (BZ#1443497)
• Previously, a kernel panic occurred when the mcelog daemon executed a huge page memory offline. This update fixes the HugeTLB feature of the Linux kernel to check for the Page Table Entry (PTE) NULL pointer in the page_check_address() function. As a result, the kernel panic no longer occurs under the described circumstances. (BZ#1444349)
• Previously, the vmw_pvscsi driver reported most successful aborts as FAILED due to a bug in vmw_pvscsi abort handler. This update fixes the handler, and successful aborts are no longer reported as FAILED. (BZ#1442966)

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 Server - AUS 6.6 x86_64
• Red Hat Enterprise Linux Server - TUS 6.6 x86_64

Fixes

• BZ - 1428319 - CVE-2017-2636 kernel: Race condition access to n_hdlc.tbuf causes double free in n_hdlc_release()
• BZ - 1461333 - CVE-2017-1000364 kernel: heap/stack gap jumping via unbounded stack allocations

CVEs

• CVE-2017-1000364
• CVE-2017-1000379
• CVE-2017-2636

References