Commit 3aeff147 authored Aug 11, 2021 by Ming Lei Committed by Connor O'Brien Jan 24, 2022

UPSTREAM: blk-mq: fix kernel panic during iterating over flush request



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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/20210811142624.618598-1-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit c2da19ed50554ce52ecbad3655c98371fe58599f)
Bug: 187129171
Signed-off-by: Connor O'Brien <connoro@google.com>
Change-Id: Id7fb5f38b0fe35331df98ec2f96e4914f15d981c

parent 54e1868c

block/blk-core.c

+0 −1

Original line number	Diff line number	Diff line
		@@ -120,7 +120,6 @@ void blk_rq_init(struct request_queue q, struct request rq)
		rq->internal_tag = -1;
		rq->start_time_ns = ktime_get_ns();
		rq->part = NULL;
		refcount_set(&rq->ref, 1);
		}
		EXPORT_SYMBOL(blk_rq_init);

block/blk-flush.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -325,6 +325,14 @@ 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);
		}