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SubjectRe: [PATCH RFC] blk-mq: fix potential uaf for 'queue_hw_ctx'
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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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