block: fix use-after-free in block flush handling

A recent commit reused the original request flags for the flush
queue handling. However, for some of the kick flush cases, the
original request was already completed. This caused a use after
free, if blk-mq wasn't used.

Fixes: 84fca1b0c461 ("block: pass failfast and driver-specific flags to flush requests")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-flush.c b/block/blk-flush.c
index 058abdb50f315f7040b76508ae7f7d9486413a9a..ce41f666de3e1d068e78698349c1629d7e118bc8 100644 (file)
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -169,9 +169,11 @@ static bool blk_flush_complete_seq(struct request *rq,
        struct request_queue *q = rq->q;
        struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
        bool queued = false, kicked;
+       unsigned int cmd_flags;
 
        BUG_ON(rq->flush.seq & seq);
        rq->flush.seq |= seq;
+       cmd_flags = rq->cmd_flags;
 
        if (likely(!error))
                seq = blk_flush_cur_seq(rq);
@@ -212,7 +214,7 @@ static bool blk_flush_complete_seq(struct request *rq,
                BUG();
        }
 
-       kicked = blk_kick_flush(q, fq, rq->cmd_flags);
+       kicked = blk_kick_flush(q, fq, cmd_flags);
        return kicked | queued;
 }