Date: Thu, 16 Feb 2017 05:46:08 +0100 From: Salvatore Bonaccorso <carnil@...ian.org> To: OSS Security Mailinglist <oss-security@...ts.openwall.com> Cc: Ben Hutchings <benh@...ian.org> Subject: Linux: CVE-2017-6001: Incomplete fix for CVE-2016-6786: perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race Hi The original fix for CVE-2016-6786 ws incomplete. Upstream has commited https://git.kernel.org/linus/321027c1fe77f892f4ea07846aeae08cefbbb290 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 -> https://cveform.mitre.org/). Commit message reads as: > commit 321027c1fe77f892f4ea07846aeae08cefbbb290 > Author: Peter Zijlstra <peterz@...radead.org> > 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 <joaodias@...gle.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org> > Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com> > Cc: Arnaldo Carvalho de Melo <acme@...nel.org> > Cc: Arnaldo Carvalho de Melo <acme@...hat.com> > Cc: Jiri Olsa <jolsa@...hat.com> > Cc: Kees Cook <keescook@...omium.org> > Cc: Linus Torvalds <torvalds@...ux-foundation.org> > Cc: Min Chong <mchong@...gle.com> > Cc: Peter Zijlstra <peterz@...radead.org> > Cc: Stephane Eranian <eranian@...gle.com> > Cc: Thomas Gleixner <tglx@...utronix.de> > Cc: Vince Weaver <vincent.weaver@...ne.edu> > Fixes: f63a8daa5812 ("perf: Fix event->ctx locking") > Link: http://lkml.kernel.org/r/20170106131444.GZ3174@twins.programming.kicks-ass.net > Signed-off-by: Ingo Molnar <mingo@...nel.org> Regards, Salvatore
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