Commit 51e35e67 authored by Zhang Wensheng's avatar Zhang Wensheng Committed by Zheng Zengkai
Browse files

block: fix null-deref in percpu_ref_put 

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5N162


CVE: NA

--------------------------------

In the use of q_usage_counter of request_queue, blk_cleanup_queue using
"wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter))"
to wait q_usage_counter becoming zero. however, if the q_usage_counter
becoming zero quickly, and percpu_ref_exit will execute and ref->data
will be freed, maybe another process will cause a null-defef problem
like below:

	CPU0                             CPU1
blk_cleanup_queue
 blk_freeze_queue
  blk_mq_freeze_queue_wait
				scsi_end_request
				 percpu_ref_get
				 ...
				 percpu_ref_put
				  atomic_long_sub_and_test
  percpu_ref_exit
   ref->data -> NULL
   				   ref->data->release(ref) -> null-deref

Fix it by setting flag(QUEUE_FLAG_USAGE_COUNT_SYNC) to add synchronization
mechanism, when ref->data->release is called, the flag will be setted,
and the "wait_event" in blk_mq_freeze_queue_wait must wait flag becoming
true as well, which will limit percpu_ref_exit to execute ahead of time.

Signed-off-by: default avatarZhang Wensheng <zhangwensheng5@huawei.com>
Reviewed-by: default avatarYu Kuai <yukuai3@huawei.com>
Signed-off-by: default avatarZheng Zengkai <zhengzengkai@huawei.com>
parent 3eb8e5e6

block/blk-core.c

+3 −1
Original line number Diff line number Diff line
@@ -385,7 +385,8 @@ void blk_cleanup_queue(struct request_queue *q) 
	 * prevent that blk_mq_run_hw_queues() accesses the hardware queues

	 * after draining finished.

	 */

	blk_freeze_queue(q);

	blk_freeze_queue_start(q);

	blk_mq_freeze_queue_wait_sync(q);



	rq_qos_exit(q);
@@ -502,6 +503,7 @@ static void blk_queue_usage_counter_release(struct percpu_ref *ref) 
	struct request_queue *q =

		container_of(ref, struct request_queue, q_usage_counter);



	blk_queue_flag_set(QUEUE_FLAG_USAGE_COUNT_SYNC, q);

	wake_up_all(&q->mq_freeze_wq);

}

block/blk-mq.c

+7 −0
Original line number Diff line number Diff line
@@ -193,6 +193,7 @@ void blk_freeze_queue_start(struct request_queue *q) 
{

	mutex_lock(&q->mq_freeze_lock);

	if (++q->mq_freeze_depth == 1) {

		blk_queue_flag_clear(QUEUE_FLAG_USAGE_COUNT_SYNC, q);

		percpu_ref_kill(&q->q_usage_counter);

		mutex_unlock(&q->mq_freeze_lock);

		if (queue_is_mq(q))
@@ -203,6 +204,12 @@ void blk_freeze_queue_start(struct request_queue *q) 
}

EXPORT_SYMBOL_GPL(blk_freeze_queue_start);



void blk_mq_freeze_queue_wait_sync(struct request_queue *q)

{

	wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter) &&

			test_bit(QUEUE_FLAG_USAGE_COUNT_SYNC, &q->queue_flags));

}



void blk_mq_freeze_queue_wait(struct request_queue *q)

{

	wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter));

include/linux/blk-mq.h

+1 −0
Original line number Diff line number Diff line
@@ -574,6 +574,7 @@ void blk_mq_freeze_queue(struct request_queue *q); 
void blk_mq_unfreeze_queue(struct request_queue *q);

void blk_freeze_queue_start(struct request_queue *q);

void blk_mq_freeze_queue_wait(struct request_queue *q);

void blk_mq_freeze_queue_wait_sync(struct request_queue *q);

int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,

				     unsigned long timeout);

include/linux/blkdev.h

+2 −0
Original line number Diff line number Diff line
@@ -643,6 +643,8 @@ struct request_queue { 
#define QUEUE_FLAG_NOWAIT       29	/* device supports NOWAIT */

/*at least one blk-mq hctx can't get driver tag */

#define QUEUE_FLAG_HCTX_WAIT	30

/* sync for q_usage_counter */

#define QUEUE_FLAG_USAGE_COUNT_SYNC    31



#define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\

				 (1 << QUEUE_FLAG_SAME_COMP) |		\