linux-kernel - [PATCH] perf_events: fix NULL point in free

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Date:	Mon, 13 Sep 2010 16:36:01 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com, eranian@...gle.com,
	robert.richter@....com
Subject: [PATCH] perf_events: fix NULL point in free_event()

Without the following patch, perf top as non-root and
paranoid cpu set causes a NULL pointer dereference in
free_event() because event->ctx is NULL.

free_event() may be called, on the error path, before
event->ctx is set.

Signed-off-by: Stephane Eranian <eranian@...gle.com>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index f29b525..a7d5e7a 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2150,7 +2150,8 @@ static void free_event(struct perf_event *event)
 	if (event->destroy)
 		event->destroy(event);
 
-	put_ctx(event->ctx);
+	if (event->ctx)
+		put_ctx(event->ctx);
 	call_rcu(&event->rcu_head, free_event_rcu);
 }
 
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