Re: [PATCH V4 0/4] blk-mq: fix request UAF related with iterating over tagset requests

John Garry
2021-05-05T11:19:49Z

On 04/05/2021 12:43, Ming Lei wrote:
>> */
>> - if (rq && rq->q == hctx->queue && rq->mq_hctx == hctx)
>> - return iter_data->fn(hctx, rq, iter_data->data, reserved);
>> + if (rq) {
>> + mdelay(50);
>> + if (rq->q == hctx->queue && rq->mq_hctx == hctx)
>> + return iter_data->fn(hctx, rq, iter_data->data, reserved);
>> + }
>> return true;
>> }
> hammmm, forget to cover bt_iter(), please test the following delta
> patch:
>
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index a3be267212b9..27815114ee3f 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -206,18 +206,28 @@ static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
> struct blk_mq_tags *tags = hctx->tags;
> bool reserved = iter_data->reserved;
> struct request *rq;
> + unsigned long flags;
> + bool ret = true;
>
> if (!reserved)
> bitnr += tags->nr_reserved_tags;
> - rq = tags->rqs[bitnr];
>
> + spin_lock_irqsave(&tags->lock, flags);
> + rq = tags->rqs[bitnr];
> /*
> * We can hit rq == NULL here, because the tagging functions
> * test and set the bit before assigning ->rqs[].
> */
> - if (rq && rq->q == hctx->queue && rq->mq_hctx == hctx)
> - return iter_data->fn(hctx, rq, iter_data->data, reserved);
> - return true;
> + if (!rq || !refcount_inc_not_zero(&rq->ref)) {
> + spin_unlock_irqrestore(&tags->lock, flags);
> + return true;
> + }
> + spin_unlock_irqrestore(&tags->lock, flags);
> +
> + if (rq->q == hctx->queue && rq->mq_hctx == hctx)
> + ret = iter_data->fn(hctx, rq, iter_data->data, reserved);
> + blk_mq_put_rq_ref(rq);
> + return ret;
> }

This looks to work ok from my testing.

Thanks,
John