bridge: Save frag_max_size between PRE_ROUTING and POST_ROUTING

As we may defragment the packet in IPv4 PRE_ROUTING and refragment
it after POST_ROUTING we should save the value of frag_max_size.

This is still very wrong as the bridge is supposed to leave the
packets intact, meaning that the right thing to do is to use the
original frag_list for fragmentation.

Unfortunately we don't currently guarantee that the frag_list is
left untouched throughout netfilter so until this changes this is
the best we can do.

There is also a spot in FORWARD where it appears that we can
forward a packet without going through fragmentation, mark it
so that we can fix it later.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_netfilter.c

@@ -404,6 +404,7 @@ static int br_nf_pre_routing_finish_bridge(struct sk_buff *skb)
 							 ETH_HLEN-ETH_ALEN);
 			/* tell br_dev_xmit to continue with forwarding */
 			nf_bridge->mask |= BRNF_BRIDGED_DNAT;
+			/* FIXME Need to refragment */
 			ret = neigh->output(neigh, skb);
 		}
 		neigh_release(neigh);
@@ -459,6 +460,10 @@ static int br_nf_pre_routing_finish(struct sk_buff *skb)
 	struct nf_bridge_info *nf_bridge = skb->nf_bridge;
 	struct rtable *rt;
 	int err;
+	int frag_max_size;
+
+	frag_max_size = IPCB(skb)->frag_max_size;
+	BR_INPUT_SKB_CB(skb)->frag_max_size = frag_max_size;
 
 	if (nf_bridge->mask & BRNF_PKT_TYPE) {
 		skb->pkt_type = PACKET_OTHERHOST;
@@ -863,13 +868,19 @@ static unsigned int br_nf_forward_arp(const struct nf_hook_ops *ops,
 static int br_nf_dev_queue_xmit(struct sk_buff *skb)
 {
 	int ret;
+	int frag_max_size;
 
+	/* This is wrong! We should preserve the original fragment
+	 * boundaries by preserving frag_list rather than refragmenting.
+	 */
 	if (skb->protocol == htons(ETH_P_IP) &&
 	    skb->len + nf_bridge_mtu_reduction(skb) > skb->dev->mtu &&
 	    !skb_is_gso(skb)) {
+		frag_max_size = BR_INPUT_SKB_CB(skb)->frag_max_size;
 		if (br_parse_ip_options(skb))
 			/* Drop invalid packet */
 			return NF_DROP;
+		IPCB(skb)->frag_max_size = frag_max_size;
 		ret = ip_fragment(skb, br_dev_queue_push_xmit);
 	} else
 		ret = br_dev_queue_push_xmit(skb);

net/bridge/br_private.h

@@ -305,10 +305,14 @@ struct net_bridge
 
 struct br_input_skb_cb {
 	struct net_device *brdev;
+
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
 	int igmp;
 	int mrouters_only;
 #endif
+
+	u16 frag_max_size;
+
 #ifdef CONFIG_BRIDGE_VLAN_FILTERING
 	bool vlan_filtered;
 #endif