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

Ming Lei
2021-05-05T14:29:19Z

On Wed, May 05, 2021 at 12:19:21PM +0100, John Garry wrote:
> 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.

OK, thanks for your test, and will add your tested-by in V4.

Thanks,
Ming