dm: make sure dm_table is binded before queue request

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4U3RI
CVE: NA

--------------------------------

We found a NULL pointer dereference problem when using dm-mpath target.
The problem is if we submit IO between loading and binding the table,
we could neither get a valid dm_target nor a valid dm table when
submitting request in dm_mq_queue_rq(). BIO based dm target could
handle this case in dm_submit_bio(). This patch fix this by checking
the mapping table before submitting request.
Signed-off-by: NZhang Yi <yi.zhang@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/md/dm-rq.c

@@ -492,8 +492,15 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
 
 	if (unlikely(!ti)) {
 		int srcu_idx;
-		struct dm_table *map = dm_get_live_table(md, &srcu_idx);
+		struct dm_table *map;
 
+		map = dm_get_live_table(md, &srcu_idx);
+		if (!map) {
+			DMERR_LIMIT("%s: mapping table unavailable, erroring io",
+				    dm_device_name(md));
+			dm_put_live_table(md, srcu_idx);
+			return BLK_STS_IOERR;
+		}
 		ti = dm_table_find_target(map, 0);
 		dm_put_live_table(md, srcu_idx);
 	}