From: Yu Kuai <yukuai3@xxxxxxxxxx>
Our syzkaller report a null pointer dereference, root cause is
following:
__blk_mq_alloc_map_and_rqs
set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs
blk_mq_alloc_map_and_rqs
blk_mq_alloc_rqso
// failed due to oom
alloc_pages_node
// set->stags[hctx_idx] is still NULL
blk_mq_free_rqs
drv_tags = set->tags[hctx_idx];
// null pointer dereference is triggered
blk_mq_clear_rq_mapping(drv_tags, ...)
This is because commit 63064be150e4 ("blk-mq:
Add blk_mq_alloc_map_and_rqs()") merged the two steps:
1) set->tags[hctx_idx] = blk_mq_alloc_rq_map()
2) blk_mq_alloc_rqs(..., set->tags[hctx_idx])
into one step:
set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs()
Since tags is not initialized yet in this case, fix the problem by
checking if tags is NULL pointer in blk_mq_clear_rq_mapping().
Fixes: 63064be150e4 ("blk-mq: Add blk_mq_alloc_map_and_rqs()")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
block/blk-mq.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8070b6c10e8d..33292c01875d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3112,8 +3112,11 @@ static void blk_mq_clear_rq_mapping(struct blk_mq_tags *drv_tags,
struct page *page;
unsigned long flags;
- /* There is no need to clear a driver tags own mapping */
- if (drv_tags == tags)
+ /*
+ * There is no need to clear mapping if driver tags is not initialized
+ * or the mapping belongs to the driver tags.
+ */
+ if (!drv_tags || drv_tags == tags)
return;
list_for_each_entry(page, &tags->page_list, lru) {
--
2.31.1
