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Subject[PATCH v2] locking/lockdep: Fix buffer overrun problem in stack_trace[]
Date
If the lockdep code is really running out of the stack_trace entries,
it is likely that buffer overrun can happen and the data immediately
after stack_trace[] will be corrupted.

If there is less than LOCK_TRACE_SIZE_IN_LONGS entries left before
the call to save_trace(), the max_entries computation will leave it
with a very large positive number because of its unsigned nature. The
subsequent call to stack_trace_save() will then corrupt the data after
stack_trace[]. Fix that by changing max_entries to a signed integer
and check for negative value before calling stack_trace_save().

Fixes: 12593b7467f9 ("locking/lockdep: Reduce space occupied by stack traces")
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/lockdep.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 32282e7112d3..32406ef0d6a2 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -482,7 +482,7 @@ static struct lock_trace *save_trace(void)
struct lock_trace *trace, *t2;
struct hlist_head *hash_head;
u32 hash;
- unsigned int max_entries;
+ int max_entries;

BUILD_BUG_ON_NOT_POWER_OF_2(STACK_TRACE_HASH_SIZE);
BUILD_BUG_ON(LOCK_TRACE_SIZE_IN_LONGS >= MAX_STACK_TRACE_ENTRIES);
@@ -490,10 +490,8 @@ static struct lock_trace *save_trace(void)
trace = (struct lock_trace *)(stack_trace + nr_stack_trace_entries);
max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries -
LOCK_TRACE_SIZE_IN_LONGS;
- trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3);

- if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES -
- LOCK_TRACE_SIZE_IN_LONGS - 1) {
+ if (max_entries <= 0) {
if (!debug_locks_off_graph_unlock())
return NULL;

@@ -502,6 +500,7 @@ static struct lock_trace *save_trace(void)

return NULL;
}
+ trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3);

hash = jhash(trace->entries, trace->nr_entries *
sizeof(trace->entries[0]), 0);
--
2.18.1
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