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Commit a5d38e7c authored by Ming Lei's avatar Ming Lei Committed by Todd Kjos
Browse files

BACKPORT: blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter 



Grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter(), and
this way will prevent the request from being re-used when ->fn is
running. The approach is same as what we do during handling timeout.

Fix request use-after-free(UAF) related with completion race or queue
releasing:

- If one rq is referred before rq->q is frozen, then queue won't be
frozen before the request is released during iteration.

- If one rq is referred after rq->q is frozen, refcount_inc_not_zero()
will return false, and we won't iterate over this request.

However, still one request UAF not covered: refcount_inc_not_zero() may
read one freed request, and it will be handled in next patch.

Tested-by: default avatarJohn Garry <john.garry@huawei.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>

Bug: 197804811
Change-Id: Ib80fe8b9f1d76d2489e41f3365fbd12d68a3b097
(cherry picked from commit 2e315dc07df009c3e29d6926871f62a30cfae394)
[Pradeep: Resolved conflicts in block/blk-mq-tag.c]
Signed-off-by: default avatarPradeep P V K <pragalla@codeaurora.org>
parent 734c36bc

block/blk-mq-tag.c

+30 −9
Original line number Diff line number Diff line
@@ -212,6 +212,16 @@ struct bt_iter_data { 
	bool reserved;

};



static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,

		unsigned int bitnr)

{

	struct request *rq = tags->rqs[bitnr];



	if (!rq || !refcount_inc_not_zero(&rq->ref))

		return NULL;

	return rq;

}



static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)

{

	struct bt_iter_data *iter_data = data;
@@ -219,18 +229,23 @@ 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;

	bool ret = true;



	if (!reserved)

		bitnr += tags->nr_reserved_tags;

	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)

		return iter_data->fn(hctx, rq, iter_data->data, reserved);

	rq = blk_mq_find_and_get_req(tags, bitnr);

	if (!rq)

		return true;



	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;

}



/**
@@ -273,6 +288,7 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data) 
	struct blk_mq_tags *tags = iter_data->tags;

	bool reserved = iter_data->reserved;

	struct request *rq;

	bool ret = true;



	if (!reserved)

		bitnr += tags->nr_reserved_tags;
@@ -281,11 +297,13 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data) 
	 * We can hit rq == NULL here, because the tagging functions

	 * test and set the bit before assining ->rqs[].

	 */

	rq = tags->rqs[bitnr];

	if (rq && blk_mq_request_started(rq))

		return iter_data->fn(rq, iter_data->data, reserved);



	rq = blk_mq_find_and_get_req(tags, bitnr);

	if (!rq)

		return true;

	if (blk_mq_request_started(rq))

		ret = iter_data->fn(rq, iter_data->data, reserved);

	blk_mq_put_rq_ref(rq);

	return ret;

}



/**
@@ -342,6 +360,9 @@ static void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags, 
 *		indicates whether or not @rq is a reserved request. Return

 *		true to continue iterating tags, false to stop.

 * @priv:	Will be passed as second argument to @fn.

 *

 * We grab one request reference before calling @fn and release it after

 * @fn returns.

 */

void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,

		busy_tag_iter_fn *fn, void *priv)

block/blk-mq.c

+9 −5
Original line number Diff line number Diff line
@@ -886,6 +886,14 @@ static bool blk_mq_req_expired(struct request *rq, unsigned long *next) 
	return false;

}



void blk_mq_put_rq_ref(struct request *rq)

{

	if (is_flush_rq(rq, rq->mq_hctx))

		rq->end_io(rq, 0);

	else if (refcount_dec_and_test(&rq->ref))

		__blk_mq_free_request(rq);

}



static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,

		struct request *rq, void *priv, bool reserved)

{
@@ -919,11 +927,7 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx, 
	if (blk_mq_req_expired(rq, next))

		blk_mq_rq_timed_out(rq, reserved);



	if (is_flush_rq(rq, hctx))

		rq->end_io(rq, 0);

	else if (refcount_dec_and_test(&rq->ref))

		__blk_mq_free_request(rq);



	blk_mq_put_rq_ref(rq);

	return true;

}

block/blk-mq.h

+1 −0
Original line number Diff line number Diff line
@@ -47,6 +47,7 @@ void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list); 
bool blk_mq_get_driver_tag(struct request *rq);

struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,

					struct blk_mq_ctx *start);

void blk_mq_put_rq_ref(struct request *rq);



/*

 * Internal helpers for allocating/freeing the request map