[tip:core/urgent] lockdep: Avoid out of bounds array reference in save_trace()

["tip-bot for Luck, Tony" <tony.luck@intel.com>]

Commit-ID:  ea5b41f9d595be354f7a50e56b28c2d72e6e88a5
Gitweb:     http://git.kernel.org/tip/ea5b41f9d595be354f7a50e56b28c2d72e6e88a5
Author:     Luck, Tony <tony.luck@intel.com>
AuthorDate: Wed, 9 Dec 2009 14:29:36 -0800
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 10 Dec 2009 08:29:33 +0100

lockdep: Avoid out of bounds array reference in save_trace()

ia64 found this the hard way (because we currently have a stub
for save_stack_trace() that does nothing). But it would be a
good idea to  be cautious in case a real save_stack_trace()
bailed out with an error before it set trace->nr_entries.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: luming.yu@intel.com
LKML-Reference: <4b2024d085302c2a2@agluck-desktop.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/lockdep.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 7a3ae56..4f8df01 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -386,7 +386,8 @@ static int save_trace(struct stack_trace *trace)
 	 * complete trace that maxes out the entries provided will be reported
 	 * as incomplete, friggin useless </rant>
 	 */
-	if (trace->entries[trace->nr_entries-1] == ULONG_MAX)
+	if (trace->nr_entries != 0 &&
+	    trace->entries[trace->nr_entries-1] == ULONG_MAX)
 		trace->nr_entries--;
 
 	trace->max_entries = trace->nr_entries;