CVE-2017-1000405

A flaw was found in the patches used to fix the 'dirtycow' vulnerability (CVE-2016-5195). An attacker, able to run local code, can exploit a race condition in transparent huge pages to modify usually read-only huge pages.

From the initial flaw description released, this issue does not affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 5, 6, 7 and Red Hat Enterprise MRG 2. They do not contain the upstream commit (8310d48b125d19fcd9521d83b8293e63eb1646aa) which allows the race condition.

This issue affects the Linux kernel packages as shipped with Red Hat Enterprise Linux 7 for ARM and Red Hat Enterprise Linux for Power LE.

Future Linux kernel updates for the respective releases may address this issue.

For further information please refer to the vulnerability article in the Customer Portal: https://access.redhat.com/security/vulnerabilities/3253921

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Disabling the use of zero page:

It is possible to prevent the zero page from being mapped as a huge page, by modifying a configuration tunable in the /sys directory as shown below. This prevents the flaw from being exercised in this method.

echo 0 > /sys/kernel/mm/transparent_hugepage/use_zero_page

Disabling huge pages:

It is possible to mitigate this flaw by disabling hugepages on a system. Some user applications may require hugepages to be performant, and may suffer a performance penalty when running without hugepages.

Red Hat has existing solutions created instructing how to disable transparent

How to disable transparent hugepages (THP) on Red Hat Enterprise Linux 7 https://access.redhat.com/solutions/1320153

If your application may require transparent huge pages, please consult your software vendor to confirm.