perf: Fix double-free of the AUX buffer

If rb->aux_refcount is decremented to zero before rb->refcount,
__rb_free_aux() may be called twice resulting in a double free of
rb->aux_pages.  Fix this by adding a check to __rb_free_aux().

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Fixes: 57ffc5ca679f ("perf: Fix AUX buffer refcounting")
Link: http://lkml.kernel.org/r/1437953468.12842.17.camel@decadent.org.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index b2be01b..c8aa3f7 100644 (file)
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -559,11 +559,13 @@ static void __rb_free_aux(struct ring_buffer *rb)
                rb->aux_priv = NULL;
        }
 
-       for (pg = 0; pg < rb->aux_nr_pages; pg++)
-               rb_free_aux_page(rb, pg);
+       if (rb->aux_nr_pages) {
+               for (pg = 0; pg < rb->aux_nr_pages; pg++)
+                       rb_free_aux_page(rb, pg);
 
-       kfree(rb->aux_pages);
-       rb->aux_nr_pages = 0;
+               kfree(rb->aux_pages);
+               rb->aux_nr_pages = 0;
+       }
 }
 
 void rb_free_aux(struct ring_buffer *rb)