CVE-2016-9644

Published: 27 November 2016

The __get_user_asm_ex macro in arch/x86/include/asm/uaccess.h in the Linux kernel 4.4.22 through 4.4.28 contains extended asm statements that are incompatible with the exception table, which allows local users to obtain root access on non-SMEP platforms via a crafted application. NOTE: this vulnerability exists because of incorrect backporting of the CVE-2016-9178 patch to older kernels.

From the Ubuntu Security Team

It was discovered that the __get_user_asm_ex implementation in the Linux kernel for x86/x86_64 contained extended asm statements that were incompatible with the exception table. A local attacker could use this to gain administrative privileges.

Notes

1c109fabbd51863475cd12ac206bdd249aee35af
was applied to the 4.4 stable series (in xenial
as 1c109fabbd51863475cd12ac206bdd249aee35af) to fix
CVE-2016-9178, and then got reverted from stable in 4.4.30
(in xenial as 2da13e7f631bb13658e00e61fdea050da25e69e7).
548acf19234dbda5a52d5a8e7e205af46e9da840 was
also very briefly applied to stable in 4.4.29, but
reverted at the same time due to problems (in xenial as
102d19689b2dd4f639a14dfd3f52ce19b5d7bb17). For xenial/4.4
derived kernels, this CVE is fixed with the reversion in
2da13e7f631bb13658e00e61fdea050da25e69e7. However, this leaves
CVE-2016-9178 unfixed.

Status

Severity score breakdown

References

• http://www.openwall.com/lists/oss-security/2016/11/03/2
• http://www.openwall.com/lists/oss-security/2016/11/07/4
• https://lwn.net/Articles/705220/
• https://ubuntu.com/security/notices/USN-3146-1
• https://ubuntu.com/security/notices/USN-3146-2
• https://ubuntu.com/security/notices/USN-3161-4
• https://www.cve.org/CVERecord?id=CVE-2016-9644
• NVD
• Launchpad
• Debian