On Wed, Feb 23, 2022 at 07:26:01PM +0800, Yu Kuai wrote: > blk_mq_realloc_hw_ctxs() will free the 'queue_hw_ctx'(e.g. undate > submit_queues through configfs for null_blk), while it might still be > used from other context(e.g. switch elevator to none): > > t1 t2 > elevator_switch > blk_mq_unquiesce_queue > blk_mq_run_hw_queues > queue_for_each_hw_ctx > // assembly code for hctx = (q)->queue_hw_ctx[i] > mov 0x48(%rbp),%rdx -> read old queue_hw_ctx > > __blk_mq_update_nr_hw_queues > blk_mq_realloc_hw_ctxs > hctxs = q->queue_hw_ctx > q->queue_hw_ctx = new_hctxs > kfree(hctxs) > movslq %ebx,%rax > mov (%rdx,%rax,8),%rdi ->uaf > Not only uaf on queue_hw_ctx, but also other similar issue on other structures, and I think the correct and easy fix is to quiesce request queue during updating nr_hw_queues, something like the following patch: diff --git a/block/blk-mq.c b/block/blk-mq.c index a05ce7725031..d8e7c3cce0dd 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -4467,8 +4467,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, if (set->nr_maps == 1 && nr_hw_queues == set->nr_hw_queues) return; - list_for_each_entry(q, &set->tag_list, tag_set_list) + list_for_each_entry(q, &set->tag_list, tag_set_list) { blk_mq_freeze_queue(q); + blk_mq_quiesce_queue(q); + } /* * Switch IO scheduler to 'none', cleaning up the data associated * with the previous scheduler. We will switch back once we are done @@ -4518,8 +4520,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, list_for_each_entry(q, &set->tag_list, tag_set_list) blk_mq_elv_switch_back(&head, q); - list_for_each_entry(q, &set->tag_list, tag_set_list) + list_for_each_entry(q, &set->tag_list, tag_set_list) { + blk_mq_unquiesce_queue(q); blk_mq_unfreeze_queue(q); + } } void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues) Thanks, Ming