diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 0956b86593603470ab6c27e0ae69af430e01708c..ddda8107aa7e3dfaf3d662b570f9baeb57bb183f 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1840,7 +1840,7 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
 	if (r)
 		goto out;
 
-	param->data_size = sizeof(*param);
+	param->data_size = offsetof(struct dm_ioctl, data);
 	r = fn(param, input_param_size);
 
 	if (unlikely(param->flags & DM_BUFFER_FULL_FLAG) &&