[PATCH AUTOSEL 5.6 18/68] blk-mq: Fix a recently introduced regression in blk_mq_realloc_hw_ctxs()

Sasha Levin
2020-04-10T04:02:50Z

From: Bart Van Assche <bvanassche@acm.org>

[ Upstream commit d0930bb8f46b8fb4a7d429c0bf1c91b3ed00a7cf ]

q->nr_hw_queues must only be updated once it is known that
blk_mq_realloc_hw_ctxs() has succeeded. Otherwise it can happen that
reallocation fails and that q->nr_hw_queues is larger than the number of
allocated hardware queues. This patch fixes the following crash if
increasing the number of hardware queues fails:

BUG: KASAN: null-ptr-deref in blk_mq_map_swqueue+0x775/0x810
Write of size 8 at addr 0000000000000118 by task check/977

CPU: 3 PID: 977 Comm: check Not tainted 5.6.0-rc1-dbg+ #8
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Call Trace:
dump_stack+0xa5/0xe6
__kasan_report.cold+0x65/0x99
kasan_report+0x16/0x20
check_memory_region+0x140/0x1b0
memset+0x28/0x40
blk_mq_map_swqueue+0x775/0x810
blk_mq_update_nr_hw_queues+0x468/0x710
nullb_device_submit_queues_store+0xf7/0x1a0 [null_blk]
configfs_write_file+0x1c4/0x250 [configfs]
__vfs_write+0x4c/0x90
vfs_write+0x145/0x2c0
ksys_write+0xd7/0x180
__x64_sys_write+0x47/0x50
do_syscall_64+0x6f/0x2f0
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fixes: ac0d6b926e74 ("block: Reduce the amount of memory required per request queue")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Johannes Thumshirn <jth@kernel.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-mq.c | 1 -
1 file changed, 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index d92088dec6c35..062bbf6c55958 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2824,7 +2824,6 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
memcpy(new_hctxs, hctxs, q->nr_hw_queues *
sizeof(*hctxs));
q->queue_hw_ctx = new_hctxs;
- q->nr_hw_queues = set->nr_hw_queues;
kfree(hctxs);
hctxs = new_hctxs;
}
--
2.20.1