scsi: scsi_debug: Fix possible UAF in sdebug_add_host_helper()

If device_register() fails in sdebug_add_host_helper(), it will goto clean
and sdbg_host will be freed, but sdbg_host->host_list will not be removed
from sdebug_host_list, then list traversal may cause UAF. Fix it.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Link: https://lore.kernel.org/r/20221117084421.58918-1-yuancan@huawei.com
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Yuan Can

drivers/scsi/scsi_debug.c

@@ -7323,8 +7323,12 @@ static int sdebug_add_host_helper(int per_host_idx)
 	dev_set_name(&sdbg_host->dev, "adapter%d", sdebug_num_hosts);
 
 	error = device_register(&sdbg_host->dev);
-	if (error)
+	if (error) {
+		spin_lock(&sdebug_host_list_lock);
+		list_del(&sdbg_host->host_list);
+		spin_unlock(&sdebug_host_list_lock);
 		goto clean;
+	}
 
 	++sdebug_num_hosts;
 	return 0;