diff options
author | Ming Lei <ming.lei@redhat.com> | 2021-08-11 17:26:24 +0300 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2021-08-17 17:33:32 +0300 |
commit | c2da19ed50554ce52ecbad3655c98371fe58599f (patch) | |
tree | 38a1fc5da3c8c9127dd717682043dc6ac4bbfeac /block | |
parent | c797b40ccc340b8a66f7a7842aecc90bf749f087 (diff) | |
download | linux-c2da19ed50554ce52ecbad3655c98371fe58599f.tar.xz |
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>
Diffstat (limited to 'block')
-rw-r--r-- | block/blk-core.c | 1 | ||||
-rw-r--r-- | block/blk-flush.c | 8 |
2 files changed, 8 insertions, 1 deletions
diff --git a/block/blk-core.c b/block/blk-core.c index 04477697ee4b..4f8449b29b21 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -122,7 +122,6 @@ 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); } |