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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Fixes: 57ffc5ca679f ("perf: Fix AUX buffer refcounting")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index b2be01b1aa9dcb7a70792fa381c264b229a106d0..c8aa3f75bc4db8ad7a2242aae6406bfd6f86f8c5 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)