V4L/DVB (13953): firedtv: add missing NULL pointer check

If there is ever going to be a FireDTV or FloppyDTV firmware which does
not provide a minimal ASCII textual descriptor for Model_Id --- or if
the descriptor is provided indirectly in a descriptor directory ---
the ieee1394 variant of the device probe of firedtv would dereference a
NULL pointer.  The firewire variant of firedtv's device probe is not
affected.

The fix makes sure that such an unexpected firmware is safely recognized
by fdtv_alloc as an unknown firmware.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/dvb/firewire/firedtv-1394.c

@@ -192,9 +192,13 @@ static int node_probe(struct device *dev)
 	int kv_len, err;
 	void *kv_str;
 
-	kv_len = (ud->model_name_kv->value.leaf.len - 2) * sizeof(quadlet_t);
+	if (ud->model_name_kv) {
+		kv_len = (ud->model_name_kv->value.leaf.len - 2) * 4;
 		kv_str = CSR1212_TEXTUAL_DESCRIPTOR_LEAF_DATA(ud->model_name_kv);
-
+	} else {
+		kv_len = 0;
+		kv_str = NULL;
+	}
 	fdtv = fdtv_alloc(dev, &fdtv_1394_backend, kv_str, kv_len);
 	if (!fdtv)
 		return -ENOMEM;