From: Ming Lei <ming.lei@xxxxxxxxxx> blk-mq: fix kernel panic during iterating over flush request Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1994424 Upstream Status: merged to for-5.14/block 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@xxxxxxxxxxxxxxx> Tested-by: "Blank-Burian, Markus, Dr." <blankburian@xxxxxxxxxxxxxxx> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: John Garry <john.garry@xxxxxxxxxx> Link: https://lore.kernel.org/r/20210811142624.618598-1-ming.lei@xxxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> diff --git a/block/blk-core.c b/block/blk-core.c index blahblah..blahblah 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 blahblah..blahblah 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); } -- https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1315 _______________________________________________ kernel mailing list -- kernel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to kernel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/kernel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam on the list, report it: https://pagure.io/fedora-infrastructure
