• Peter Zijlstra's avatar
    perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race · 321027c1
    Peter Zijlstra authored
    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:
    
      f63a8daa ("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: default avatarJohn Dias <joaodias@google.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Min Chong <mchong@google.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Fixes: f63a8daa ("perf: Fix event->ctx locking")
    Link: http://lkml.kernel.org/r/20170106131444.GZ3174@twins.programming.kicks-ass.netSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    321027c1
core.c 255 KB