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>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 7a3ae56b3a7..4f8df01dbe5 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;