This is a note to let you know that I've just added the patch titled blk-mq: fix null pointer dereference in blk_mq_clear_rq_mapping() to the 6.0-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: blk-mq-fix-null-pointer-dereference-in-blk_mq_clear_.patch and it can be found in the queue-6.0 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 9225e1c36291de514ada76fb6088cfc4cd6b8846 Author: Yu Kuai <yukuai3@xxxxxxxxxx> Date: Tue Oct 11 22:22:53 2022 +0800 blk-mq: fix null pointer dereference in blk_mq_clear_rq_mapping() [ Upstream commit 76dd298094f484c6250ebd076fa53287477b2328 ] 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_rqs // failed due to oom alloc_pages_node // set->tags[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> Reviewed-by: John Garry <john.garry@xxxxxxxxxx> Link: https://lore.kernel.org/r/20221011142253.4015966-1-yukuai1@xxxxxxxxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/block/blk-mq.c b/block/blk-mq.c index 887b8682eb69..fe840536e6ac 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3028,8 +3028,11 @@ 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) {