bridge br_multicast: Don't refer to BR_INPUT_SKB_CB(skb)->mrouters_only without IGMP snooping.

Without CONFIG_BRIDGE_IGMP_SNOOPING,
BR_INPUT_SKB_CB(skb)->mrouters_only is not appropriately
initialized, so we can see garbage.

A clear option to fix this is to set it even without that
config, but we cannot optimize out the branch.

Let's introduce a macro that returns value of mrouters_only
and let it return 0 without CONFIG_BRIDGE_IGMP_SNOOPING.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_device.c

@@ -40,7 +40,7 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 			goto out;
 
 		mdst = br_mdb_get(br, skb);
-		if (mdst || BR_INPUT_SKB_CB(skb)->mrouters_only)
+		if (mdst || BR_INPUT_SKB_CB_MROUTERS_ONLY(skb))
 			br_multicast_deliver(mdst, skb);
 		else
 			br_flood_deliver(br, skb);

net/bridge/br_input.c

@@ -70,7 +70,7 @@ int br_handle_frame_finish(struct sk_buff *skb)
 
 	if (is_multicast_ether_addr(dest)) {
 		mdst = br_mdb_get(br, skb);
-		if (mdst || BR_INPUT_SKB_CB(skb)->mrouters_only) {
+		if (mdst || BR_INPUT_SKB_CB_MROUTERS_ONLY(skb)) {
 			if ((mdst && !hlist_unhashed(&mdst->mglist)) ||
 			    br_multicast_is_router(br))
 				skb2 = skb;

net/bridge/br_private.h

@@ -206,12 +206,20 @@ struct net_bridge
 
 struct br_input_skb_cb {
 	struct net_device *brdev;
+#ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 	int igmp;
 	int mrouters_only;
+#endif
 };
 
 #define BR_INPUT_SKB_CB(__skb)	((struct br_input_skb_cb *)(__skb)->cb)
 
+#ifdef CONFIG_BRIDGE_IGMP_SNOOPING
+# define BR_INPUT_SKB_CB_MROUTERS_ONLY(__skb)	(BR_INPUT_SKB_CB(__skb)->mrouters_only)
+#else
+# define BR_INPUT_SKB_CB_MROUTERS_ONLY(__skb)	(0)
+#endif
+
 extern struct notifier_block br_device_notifier;
 extern const u8 br_group_address[ETH_ALEN];