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Date: Tue, 8 Dec 2015 20:32:03 -0500 (EST)
From: Wade Mealing <>
Subject: CVE request - Linux kernel - Fix handling of stored error in a
 negatively instantiated user key


A bug was found by Dmitry Vyukov (of Google engineering) in the Linux
kernel key management code.

A malicious user with a local account may be able to escalate privileges
and take control of local system by abusing the user key subsystem.

>From the patch: 

If a user key gets negatively instantiated, an error code is cached in the
payload area.  A negatively instantiated key may be then be positively
instantiated by updating it with valid data.  However, the ->update key
type method must be aware that the error code may be there.

The paging address is predictable and mappable as userspace memory and can
be used by abused by an attacker to escalate privileges.

This is not the same issue as CVE-2015-7872, this issue persists
after the fix is applied.  I have only seen this affected on the 4.4 
release candidates.


Wade Mealing

Upstream fix

Red Hat Bugzilla:

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