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Date: Thu, 16 Feb 2017 05:46:08 +0100
From: Salvatore Bonaccorso <>
To: OSS Security Mailinglist <>
Cc: Ben Hutchings <>
Subject: Linux: CVE-2017-6001: Incomplete fix for CVE-2016-6786: perf/core:
 Fix concurrent sys_perf_event_open() vs. 'move_group' race


The original fix for CVE-2016-6786 ws incomplete. Upstream has

which is in v4.10-rc4 (and also backported to 4.9.x in v4.9.7). This
has been assigned a new CVE identifier: CVE-2017-6001 (assigned via ->

Commit message reads as:

> commit 321027c1fe77f892f4ea07846aeae08cefbbb290
> Author: Peter Zijlstra <>
> Date:   Wed Jan 11 21:09:50 2017 +0100
>     perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race
>     Di Shen reported a race between two concurrent sys_perf_event_open()
>     calls where both try and move the same pre-existing software group
>     into a hardware context.
>     The problem is exactly that described in commit:
>       f63a8daa5812 ("perf: Fix event->ctx locking")
>     ... where, while we wait for a ctx->mutex acquisition, the event->ctx
>     relation can have changed under us.
>     That very same commit failed to recognise sys_perf_event_context() as an
>     external access vector to the events and thereby didn't apply the
>     established locking rules correctly.
>     So while one sys_perf_event_open() call is stuck waiting on
>     mutex_lock_double(), the other (which owns said locks) moves the group
>     about. So by the time the former sys_perf_event_open() acquires the
>     locks, the context we've acquired is stale (and possibly dead).
>     Apply the established locking rules as per perf_event_ctx_lock_nested()
>     to the mutex_lock_double() for the 'move_group' case. This obviously means
>     we need to validate state after we acquire the locks.
>     Reported-by: Di Shen (Keen Lab)
>     Tested-by: John Dias <>
>     Signed-off-by: Peter Zijlstra (Intel) <>
>     Cc: Alexander Shishkin <>
>     Cc: Arnaldo Carvalho de Melo <>
>     Cc: Arnaldo Carvalho de Melo <>
>     Cc: Jiri Olsa <>
>     Cc: Kees Cook <>
>     Cc: Linus Torvalds <>
>     Cc: Min Chong <>
>     Cc: Peter Zijlstra <>
>     Cc: Stephane Eranian <>
>     Cc: Thomas Gleixner <>
>     Cc: Vince Weaver <>
>     Fixes: f63a8daa5812 ("perf: Fix event->ctx locking")
>     Link:
>     Signed-off-by: Ingo Molnar <>


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