From: Ming Lei <ming.lei@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, Bart Van Assche <bvanassche@acm.org>,
Christoph Hellwig <hch@lst.de>,
John Garry <john.garry@huawei.com>,
Ming Lei <ming.lei@redhat.com>,
"Blank-Burian, Markus, Dr." <blankburian@uni-muenster.de>
Subject: [PATCH] blk-mq: fix kernel panic during iterating over flush request
Date: Wed, 11 Aug 2021 22:26:24 +0800 [thread overview]
Message-ID: <20210811142624.618598-1-ming.lei@redhat.com> (raw)
For fixing use-after-free during iterating over requests, we grabbed
request's refcount before calling ->fn in commit 2e315dc07df0 ("blk-mq:
grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter").
Turns out this way may cause kernel panic when iterating over one flush
request:
1) old flush request's tag is just released, and this tag is reused by
one new request, but ->rqs[] isn't updated yet
2) the flush request can be re-used for submitting one new flush command,
so blk_rq_init() is called at the same time
3) meantime blk_mq_queue_tag_busy_iter() is called, and old flush request
is retrieved from ->rqs[tag]; when blk_mq_put_rq_ref() is called,
flush_rq->end_io may not be updated yet, so NULL pointer dereference
is triggered in blk_mq_put_rq_ref().
Fix the issue by calling refcount_set(&flush_rq->ref, 1) after
flush_rq->end_io is set. So far the only other caller of blk_rq_init() is
scsi_ioctl_reset() in which the request doesn't enter block IO stack and
the request reference count isn't used, so the change is safe.
Fixes: 2e315dc07df0 ("blk-mq: grab rq->refcount before calling ->fn in
blk_mq_tagset_busy_iter")
Reported-by: "Blank-Burian, Markus, Dr." <blankburian@uni-muenster.de>
Tested-by: "Blank-Burian, Markus, Dr." <blankburian@uni-muenster.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-core.c | 1 -
block/blk-flush.c | 8 ++++++++
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 0874bc2fcdb4..b5098739f72a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -121,7 +121,6 @@ void blk_rq_init(struct request_queue *q, struct request *rq)
rq->internal_tag = BLK_MQ_NO_TAG;
rq->start_time_ns = ktime_get_ns();
rq->part = NULL;
- refcount_set(&rq->ref, 1);
blk_crypto_rq_set_defaults(rq);
}
EXPORT_SYMBOL(blk_rq_init);
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 1002f6c58181..4912c8dbb1d8 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -329,6 +329,14 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
flush_rq->rq_flags |= RQF_FLUSH_SEQ;
flush_rq->rq_disk = first_rq->rq_disk;
flush_rq->end_io = flush_end_io;
+ /*
+ * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
+ * implied in refcount_inc_not_zero() called from
+ * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
+ * and READ flush_rq->end_io
+ */
+ smp_wmb();
+ refcount_set(&flush_rq->ref, 1);
blk_flush_queue_rq(flush_rq, false);
}
--
2.31.1
next reply other threads:[~2021-08-11 14:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-11 14:26 Ming Lei [this message]
2021-08-12 8:57 ` [PATCH] blk-mq: fix kernel panic during iterating over flush request Christoph Hellwig
2021-08-12 10:20 ` John Garry
2021-08-12 11:47 ` Xiaoguang Wang
2021-08-12 13:04 ` Ming Lei
2021-08-12 13:19 ` Xiaoguang Wang
2021-08-17 0:58 ` Ming Lei
2021-08-17 14:33 ` Jens Axboe
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