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From: Ben Hutchings <ben@decadent.org.uk>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] perf: Avoid double-free of AUX buffer
Date: Mon, 27 Jul 2015 00:31:08 +0100
Message-ID: <1437953468.12842.17.camel@decadent.org.uk> (raw)


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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().

Fixes: 57ffc5ca679f ("perf: Fix AUX buffer refcounting")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
Found by inspection, and the fix is compile-tested only.

I think both commit 57ffc5ca679f and this should go to stable, but
that's up to you.

Ben.

 kernel/events/ring_buffer.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index b2be01b..c8aa3f7 100644
--- 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)
-- 
Ben Hutchings
Any sufficiently advanced bug is indistinguishable from a feature.


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Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-26 23:31 Ben Hutchings [this message]
2015-08-12 12:31 ` [tip:perf/core] perf: Fix double-free of the " tip-bot for Ben Hutchings

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