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authorMing Lei <ming.lei@redhat.com>2021-08-11 22:26:24 +0800
committerJens Axboe <axboe@kernel.dk>2021-08-17 08:33:32 -0600
commitc2da19ed50554ce52ecbad3655c98371fe58599f (patch)
tree38a1fc5da3c8c9127dd717682043dc6ac4bbfeac /block/blk.h
parentc797b40ccc340b8a66f7a7842aecc90bf749f087 (diff)
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>
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