Messages in this thread | | | Subject | Re: [PATCH RFC] blk-mq: fix potential uaf for 'queue_hw_ctx' | From | "yukuai (C)" <> | Date | Thu, 24 Feb 2022 09:29:09 +0800 |
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在 2022/02/23 22:30, Ming Lei 写道: > 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) Hi, Ming
If blk_mq_quiesce_queue() is called from __blk_mq_update_nr_hw_queues() first, and then swithing elevator to none won't trigger the problem. However, what if blk_mq_unquiesce_queue() from switching elevator decrease quiesce_depth to 0 first, and then blk_mq_quiesce_queue() is called from __blk_mq_update_nr_hw_queues(), it seems to me such concurrent scenarios still exist.
Thanks, Kuai > > > > Thanks, > Ming > > . >
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