[PATCH AUTOSEL 5.10 11/41] blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter

[PATCH AUTOSEL 5.10 11/41] blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter

[Sasha Levin]

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit 2e315dc07df009c3e29d6926871f62a30cfae394 ]

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: John Garry <john.garry@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210511152236.763464-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-mq-tag.c | 44 +++++++++++++++++++++++++++++++++-----------
 block/blk-mq.c     | 14 +++++++++-----
 block/blk-mq.h     |  1 +
 3 files changed, 43 insertions(+), 16 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 9c92053e704d..6772c3728865 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -199,6 +199,16 @@ 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;
@@ -206,18 +216,22 @@ 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 && rq->mq_hctx == hctx)
-		return iter_data->fn(hctx, rq, iter_data->data, reserved);
-	return true;
+	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;
 }
 
 /**
@@ -264,6 +278,8 @@ 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->flags & BT_TAG_ITER_RESERVED;
 	struct request *rq;
+	bool ret = true;
+	bool iter_static_rqs = !!(iter_data->flags & BT_TAG_ITER_STATIC_RQS);
 
 	if (!reserved)
 		bitnr += tags->nr_reserved_tags;
@@ -272,16 +288,19 @@ 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 assigning ->rqs[].
 	 */
-	if (iter_data->flags & BT_TAG_ITER_STATIC_RQS)
+	if (iter_static_rqs)
 		rq = tags->static_rqs[bitnr];
 	else
-		rq = tags->rqs[bitnr];
+		rq = blk_mq_find_and_get_req(tags, bitnr);
 	if (!rq)
 		return true;
-	if ((iter_data->flags & BT_TAG_ITER_STARTED) &&
-	    !blk_mq_request_started(rq))
-		return true;
-	return iter_data->fn(rq, iter_data->data, reserved);
+
+	if (!(iter_data->flags & BT_TAG_ITER_STARTED) ||
+	    blk_mq_request_started(rq))
+		ret = iter_data->fn(rq, iter_data->data, reserved);
+	if (!iter_static_rqs)
+		blk_mq_put_rq_ref(rq);
+	return ret;
 }
 
 /**
@@ -348,6 +367,9 @@ void blk_mq_all_tag_iter(struct blk_mq_tags *tags, busy_tag_iter_fn *fn,
  *		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)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4bf9449b4586..50d3527a5d97 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -927,6 +927,14 @@ 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)
 {
@@ -960,11 +968,7 @@ 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;
 }
 
diff --git a/block/blk-mq.h b/block/blk-mq.h
index d2359f7cfd5f..f792a0920ebb 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -47,6 +47,7 @@ void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
 void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list);
 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
-- 
2.30.2

[PATCH AUTOSEL 5.10 12/41] blk-mq: clear stale request in tags->rq[] before freeing one request pool

[Sasha Levin]

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit bd63141d585bef14f4caf111f6d0e27fe2300ec6 ]

refcount_inc_not_zero() in bt_tags_iter() still may read one freed
request.

Fix the issue by the following approach:

1) hold a per-tags spinlock when reading ->rqs[tag] and calling
refcount_inc_not_zero in bt_tags_iter()

2) clearing stale request referred via ->rqs[tag] before freeing
request pool, the per-tags spinlock is held for clearing stale
->rq[tag]

So after we cleared stale requests, bt_tags_iter() won't observe
freed request any more, also the clearing will wait for pending
request reference.

The idea of clearing ->rqs[] is borrowed from John Garry's previous
patch and one recent David's patch.

Tested-by: John Garry <john.garry@huawei.com>
Reviewed-by: David Jeffery <djeffery@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210511152236.763464-4-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-mq-tag.c |  9 +++++++--
 block/blk-mq-tag.h |  6 ++++++
 block/blk-mq.c     | 46 +++++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 54 insertions(+), 7 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 6772c3728865..c4f2f6c123ae 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -202,10 +202,14 @@ struct bt_iter_data {
 static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,
 		unsigned int bitnr)
 {
-	struct request *rq = tags->rqs[bitnr];
+	struct request *rq;
+	unsigned long flags;
 
+	spin_lock_irqsave(&tags->lock, flags);
+	rq = tags->rqs[bitnr];
 	if (!rq || !refcount_inc_not_zero(&rq->ref))
-		return NULL;
+		rq = NULL;
+	spin_unlock_irqrestore(&tags->lock, flags);
 	return rq;
 }
 
@@ -538,6 +542,7 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
 
 	tags->nr_tags = total_tags;
 	tags->nr_reserved_tags = reserved_tags;
+	spin_lock_init(&tags->lock);
 
 	if (flags & BLK_MQ_F_TAG_HCTX_SHARED)
 		return tags;
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index 7d3e6b333a4a..f887988e5ef6 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -20,6 +20,12 @@ struct blk_mq_tags {
 	struct request **rqs;
 	struct request **static_rqs;
 	struct list_head page_list;
+
+	/*
+	 * used to clear request reference in rqs[] before freeing one
+	 * request pool
+	 */
+	spinlock_t lock;
 };
 
 extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags,
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 50d3527a5d97..00d6ed2fe812 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2276,6 +2276,45 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 	return BLK_QC_T_NONE;
 }
 
+static size_t order_to_size(unsigned int order)
+{
+	return (size_t)PAGE_SIZE << order;
+}
+
+/* called before freeing request pool in @tags */
+static void blk_mq_clear_rq_mapping(struct blk_mq_tag_set *set,
+		struct blk_mq_tags *tags, unsigned int hctx_idx)
+{
+	struct blk_mq_tags *drv_tags = set->tags[hctx_idx];
+	struct page *page;
+	unsigned long flags;
+
+	list_for_each_entry(page, &tags->page_list, lru) {
+		unsigned long start = (unsigned long)page_address(page);
+		unsigned long end = start + order_to_size(page->private);
+		int i;
+
+		for (i = 0; i < set->queue_depth; i++) {
+			struct request *rq = drv_tags->rqs[i];
+			unsigned long rq_addr = (unsigned long)rq;
+
+			if (rq_addr >= start && rq_addr < end) {
+				WARN_ON_ONCE(refcount_read(&rq->ref) != 0);
+				cmpxchg(&drv_tags->rqs[i], rq, NULL);
+			}
+		}
+	}
+
+	/*
+	 * Wait until all pending iteration is done.
+	 *
+	 * Request reference is cleared and it is guaranteed to be observed
+	 * after the ->lock is released.
+	 */
+	spin_lock_irqsave(&drv_tags->lock, flags);
+	spin_unlock_irqrestore(&drv_tags->lock, flags);
+}
+
 void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
 		     unsigned int hctx_idx)
 {
@@ -2294,6 +2333,8 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
 		}
 	}
 
+	blk_mq_clear_rq_mapping(set, tags, hctx_idx);
+
 	while (!list_empty(&tags->page_list)) {
 		page = list_first_entry(&tags->page_list, struct page, lru);
 		list_del_init(&page->lru);
@@ -2353,11 +2394,6 @@ struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
 	return tags;
 }
 
-static size_t order_to_size(unsigned int order)
-{
-	return (size_t)PAGE_SIZE << order;
-}
-
 static int blk_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
 			       unsigned int hctx_idx, int node)
 {
-- 
2.30.2

[PATCH AUTOSEL 5.10 21/41] block: fix race between adding/removing rq qos and normal IO

[Sasha Levin]

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit 2cafe29a8d03f02a3d16193bdaae2f3e82a423f9 ]

Yi reported several kernel panics on:

[16687.001777] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
...
[16687.163549] pc : __rq_qos_track+0x38/0x60

or

[  997.690455] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
...
[  997.850347] pc : __rq_qos_done+0x2c/0x50

Turns out it is caused by race between adding rq qos(wbt) and normal IO
because rq_qos_add can be run when IO is being submitted, fix this issue
by freezing queue before adding/deleting rq qos to queue.

rq_qos_exit() needn't to freeze queue because it is called after queue
has been frozen.

iolatency calls rq_qos_add() during allocating queue, so freezing won't
add delay because queue usage refcount works at atomic mode at that
time.

iocost calls rq_qos_add() when writing cgroup attribute file, that is
fine to freeze queue at that time since we usually freeze queue when
storing to queue sysfs attribute, meantime iocost only exists on the
root cgroup.

wbt_init calls it in blk_register_queue() and queue sysfs attribute
store(queue_wb_lat_store() when write it 1st time in case of !BLK_WBT_MQ),
the following patch will speedup the queue freezing in wbt_init.

Reported-by: Yi Zhang <yi.zhang@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Link: https://lore.kernel.org/r/20210609015822.103433-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-rq-qos.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/block/blk-rq-qos.h b/block/blk-rq-qos.h
index 2bc43e94f4c4..2bcb3495e376 100644
--- a/block/blk-rq-qos.h
+++ b/block/blk-rq-qos.h
@@ -7,6 +7,7 @@
 #include <linux/blk_types.h>
 #include <linux/atomic.h>
 #include <linux/wait.h>
+#include <linux/blk-mq.h>
 
 #include "blk-mq-debugfs.h"
 
@@ -99,8 +100,21 @@ static inline void rq_wait_init(struct rq_wait *rq_wait)
 
 static inline void rq_qos_add(struct request_queue *q, struct rq_qos *rqos)
 {
+	/*
+	 * No IO can be in-flight when adding rqos, so freeze queue, which
+	 * is fine since we only support rq_qos for blk-mq queue.
+	 *
+	 * Reuse ->queue_lock for protecting against other concurrent
+	 * rq_qos adding/deleting
+	 */
+	blk_mq_freeze_queue(q);
+
+	spin_lock_irq(&q->queue_lock);
 	rqos->next = q->rq_qos;
 	q->rq_qos = rqos;
+	spin_unlock_irq(&q->queue_lock);
+
+	blk_mq_unfreeze_queue(q);
 
 	if (rqos->ops->debugfs_attrs)
 		blk_mq_debugfs_register_rqos(rqos);
@@ -110,12 +124,22 @@ static inline void rq_qos_del(struct request_queue *q, struct rq_qos *rqos)
 {
 	struct rq_qos **cur;
 
+	/*
+	 * See comment in rq_qos_add() about freezing queue & using
+	 * ->queue_lock.
+	 */
+	blk_mq_freeze_queue(q);
+
+	spin_lock_irq(&q->queue_lock);
 	for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
 		if (*cur == rqos) {
 			*cur = rqos->next;
 			break;
 		}
 	}
+	spin_unlock_irq(&q->queue_lock);
+
+	blk_mq_unfreeze_queue(q);
 
 	blk_mq_debugfs_unregister_rqos(rqos);
 }
-- 
2.30.2