dm ioctl: forbid multiple device specifiers

Exactly one of name, uuid or device must be specified when referencing
an existing device.  This removes the ambiguity (risking the wrong
device being updated) if two conflicting parameters were specified.
Previously one parameter got used and any others were ignored silently.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-ioctl.c

@@ -739,10 +739,16 @@ static struct hash_cell *__find_device_hash_cell(struct dm_ioctl *param)
 	struct hash_cell *hc = NULL;
 
 	if (*param->uuid) {
+		if (*param->name || param->dev)
+			return NULL;
+
 		hc = __get_uuid_cell(param->uuid);
 		if (!hc)
 			return NULL;
 	} else if (*param->name) {
+		if (param->dev)
+			return NULL;
+
 		hc = __get_name_cell(param->name);
 		if (!hc)
 			return NULL;