[PATCH 3.18.y 4.4.y 4.9.y] block: blk_init_allocated_queue() set q->fq as NULL in the fail case

[Alessio Balsini]

From: xiao jin <jin.xiao@xxxxxxxxx>

commit 54648cf1ec2d7f4b6a71767799c45676a138ca24 upstream.

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
blk_init_allocated_queue().

Fixes: commit 7c94e1c157a2 ("block: introduce blk_flush_queue to drive flush machinery")
Cc: <stable@xxxxxxxxxxxxxxx>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Reviewed-by: Bart Van Assche <bart.vanassche@xxxxxxx>
Signed-off-by: xiao jin <jin.xiao@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Alessio Balsini <balsini@xxxxxxxxxxx>
---
 block/blk-core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 50d77c90070d..7662f97dded6 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -870,6 +870,7 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
 
 fail:
 	blk_free_flush_queue(q->fq);
+	q->fq = NULL;
 	return NULL;
 }
 EXPORT_SYMBOL(blk_init_allocated_queue);
-- 
2.22.0.770.g0f2c4a37fd-goog