On Mon, Feb 17, 2020 at 01:08:37PM -0800, Bart Van Assche wrote:
> 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
>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Johannes Thumshirn <jth@xxxxxxxxxx>
> Cc: Keith Busch <kbusch@xxxxxxxxxx>
> Fixes: ac0d6b926e74 ("block: Reduce the amount of memory required per request queue")
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> block/blk-mq.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 2b9f490f5a64..5408098b58f2 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;
> }
Looks correct, since ->nr_hw_queues needs to be updated after hctxs are
initialized successfully:
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
thanks,
Ming
