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SubjectRe: [PATCH] block: fix uint overflow when merging io requests
On 06/27/2014 03:24 PM, Junxiao Bi wrote:
> 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.
Any body help review this patch?
blk_rq_sectors(), bio_sectors(), blk_rq_get_max_sectors() are all uint.

blk_rq_sectors(req) + bio_sectors(bio) > blk_rq_get_max_sectors(req)

This checking is bypassed when overflow happen. It will cause an io
request's
length less than its child bio's size.

Thanks,
Junxiao.
>
> Signed-off-by: Junxiao Bi <junxiao.bi@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;



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