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Subject[PATCH] blk_init_allocated_queue() set q->fq as NULL in the fail case
We find the memory use-after-free issue in __blk_drain_queue()
on the kernel 4.14. After read the latest kernel 4.18-rc6 we
think it has the same problem.

Memory is allocated for q->fq in the blk_init_allocated_queue().
If the elevator init function called with error return, it will
run into the fail case to free the q->fq.

Then the __blk_drain_queue() uses the same memory after the free
of the q->fq, it will lead to the unpredictable event.

The patch is to set q->fq as NULL in the fail case of

Signed-off-by: xiao jin <>
block/blk-core.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index b888175..52635e2 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1072,6 +1072,7 @@ int blk_init_allocated_queue(struct request_queue *q)
q->exit_rq_fn(q, q->fq->flush_rq);
+ q->fq = NULL;
return -ENOMEM;
 \ /
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