Commit 828b6f0e authored Jan 27, 2016 by Peter Zijlstra Committed by Ingo Molnar Jan 29, 2016

perf: Fix NULL deref



Dan reported:

  1229                  if (ctx->task == TASK_TOMBSTONE ||
  1230                      !atomic_inc_not_zero(&ctx->refcount)) {
  1231                          raw_spin_unlock(&ctx->lock);
  1232                          ctx = NULL;
                                ^^^^^^^^^^
ctx is NULL.

  1233                  }
  1234
  1235                  WARN_ON_ONCE(ctx->task != task);
                                     ^^^^^^^^^^^^^^^^^
The patch adds a NULL dereference.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
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: 63b6da39 ("perf: Fix perf_event_exit_task() race")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 8f04b853

kernel/events/core.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1230,10 +1230,10 @@ retry:
		!atomic_inc_not_zero(&ctx->refcount)) {
		raw_spin_unlock(&ctx->lock);
		ctx = NULL;
		}

		} else {
		WARN_ON_ONCE(ctx->task != task);
		}
		}
		rcu_read_unlock();
		if (!ctx)
		local_irq_restore(*flags);

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