blk-mq: fix tags UAF when shrinking q->nr_hw_queues

[ Upstream commit 6be6d112 ]

When nr_hw_queues shrink, we free the excess tags before realloc'ing
hw_ctxs for each queue. During that resize, we may need to access those
tags, like blk_mq_tag_idle(hctx) will access queue shared tags.

This can cause a slab use-after-free, as reported by KASAN. Fix it by
moving the releasing of excess tags to the end.

Fixes: e1dd7bc9 ("blk-mq: fix tags leak when shrink nr_hw_queues")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/all/CAHj4cs_CK63uoDpGBGZ6DN4OCTpzkR3UaVgK=LX8Owr8ej2ieQ@mail.gmail.com/


Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20230908005702.2183908-1-chengming.zhou@linux.dev


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>