This uint overflow will cause req->__data_len < req->bio->bi_size,
this will confuse block layer and device driver.
I watched a panic caused by this when mkfs.ext4 a volume of a large
virtual disk on vm guest, blkdev_issue_discard() issue two bio with
a total size over UINT_MAX, but the check in ll_back_merge_fn() didn't
take affect due to the overflow and they were merged into one request.
After the request is done, in blk_end_request_all(), BUG_ON(pending)
was triggered and kernel panic. "pending" is true is because
blk_update_request() return ture when req->__data_len is less
than req->bio->bi_size.
Signed-off-by: Junxiao Bi <junxiao...@oracle.com>
---
block/blk-merge.c | 40 ++++++++++++++++++++++++++++++++++------
1 file changed, 34 insertions(+), 6 deletions(-)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index b3bf0df..340c0a7 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -325,11 +325,41 @@ no_merge:
return 0;
}
-int ll_back_merge_fn(struct request_queue *q, struct request *req,
+static inline bool ll_allow_merge_bio(struct request *req,
struct bio *bio)
{
if (blk_rq_sectors(req) + bio_sectors(bio) >
- blk_rq_get_max_sectors(req)) {
+ blk_rq_get_max_sectors(req))
+ return false;
+
+ /* check uint overflow */
+ if (blk_rq_sectors(req) + bio_sectors(bio) < blk_rq_sectors(req)
+ || blk_rq_sectors(req) + bio_sectors(bio) < bio_sectors(bio))
+ return false;
+
+ return true;
+}
+
+static inline bool ll_allow_merge_req(struct request *req,
+ struct request *next)
+{
+ if (blk_rq_sectors(req) + blk_rq_sectors(next) >
+ blk_rq_get_max_sectors(req))
+ return false;
+
+ /* check uint overflow */
+ if (blk_rq_sectors(req) + blk_rq_sectors(next) < blk_rq_sectors(req)
+ || blk_rq_sectors(req) + blk_rq_sectors(next) <
+ blk_rq_sectors(next))
+ return false;
+
+ return true;
+}
+
+int ll_back_merge_fn(struct request_queue *q, struct request *req,
+ struct bio *bio)
+{
+ if (!ll_allow_merge_bio(req, bio)) {
req->cmd_flags |= REQ_NOMERGE;
if (req == q->last_merge)
q->last_merge = NULL;
@@ -346,8 +376,7 @@ int ll_back_merge_fn(struct request_queue *q, struct
request *req,
int ll_front_merge_fn(struct request_queue *q, struct request *req,
struct bio *bio)
{
- if (blk_rq_sectors(req) + bio_sectors(bio) >
- blk_rq_get_max_sectors(req)) {
+ if (!ll_allow_merge_bio(req, bio)) {
req->cmd_flags |= REQ_NOMERGE;
if (req == q->last_merge)
q->last_merge = NULL;
@@ -389,8 +418,7 @@ static int ll_merge_requests_fn(struct request_queue *q,
struct request *req,
/*
* Will it become too large?
*/
- if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
- blk_rq_get_max_sectors(req))
+ if (!ll_allow_merge_req(req, next))
return 0;
total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
--
1.7.9.5
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