linux-kernel - [v3.0 stable version][PATCH 1/2] ring-buffer: Fix NULL pointer if rb_set_head

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Date:	Fri, 30 Nov 2012 11:16:43 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org, stable <stable@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [v3.0 stable version][PATCH 1/2] ring-buffer: Fix NULL pointer if
 rb_set_head_page() fails

The function rb_set_head_page() searches the list of ring buffer
pages for a the page that has the HEAD page flag set. If it does
not find it, it will do a WARN_ON(), disable the ring buffer and
return NULL, as this should never happen.

But if this bug happens to happen, not all callers of this function
can handle a NULL pointer being returned from it. That needs to be
fixed.

Cc: stable@...r.kernel.org # 3.0+
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/trace/ring_buffer.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

Index: linux-test.git/kernel/trace/ring_buffer.c
===================================================================
--- linux-test.git.orig/kernel/trace/ring_buffer.c
+++ linux-test.git/kernel/trace/ring_buffer.c
@@ -2926,6 +2926,8 @@ rb_get_reader_page(struct ring_buffer_pe
 	 * Splice the empty reader page into the list around the head.
 	 */
 	reader = rb_set_head_page(cpu_buffer);
+	if (!reader)
+		goto out;
 	cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
 	cpu_buffer->reader_page->list.prev = reader->list.prev;
 


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