bridge: move mac header copying into br_netfilter

The mac header only has to be copied back into the skb for
fragments generated by ip_fragment(), which only happens
for bridge forwarded packets with nf-call-iptables=1 && active nf_defrag.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter_bridge.h

@@ -44,36 +44,6 @@ static inline void nf_bridge_update_protocol(struct sk_buff *skb)
 		skb->protocol = htons(ETH_P_PPP_SES);
 }
 
-/* Fill in the header for fragmented IP packets handled by
- * the IPv4 connection tracking code.
- *
- * Only used in br_forward.c
- */
-static inline int nf_bridge_copy_header(struct sk_buff *skb)
-{
-	int err;
-	unsigned int header_size;
-
-	nf_bridge_update_protocol(skb);
-	header_size = ETH_HLEN + nf_bridge_encap_header_len(skb);
-	err = skb_cow_head(skb, header_size);
-	if (err)
-		return err;
-
-	skb_copy_to_linear_data_offset(skb, -header_size,
-				       skb->nf_bridge->data, header_size);
-	__skb_push(skb, nf_bridge_encap_header_len(skb));
-	return 0;
-}
-
-static inline int nf_bridge_maybe_copy_header(struct sk_buff *skb)
-{
-	if (skb->nf_bridge &&
-	    skb->nf_bridge->mask & (BRNF_BRIDGED | BRNF_BRIDGED_DNAT))
-		return nf_bridge_copy_header(skb);
-  	return 0;
-}
-
 static inline unsigned int nf_bridge_mtu_reduction(const struct sk_buff *skb)
 {
 	if (unlikely(skb->nf_bridge->mask & BRNF_PPPoE))
@@ -119,7 +89,6 @@ static inline void br_drop_fake_rtable(struct sk_buff *skb)
 }
 
 #else
-#define nf_bridge_maybe_copy_header(skb)	(0)
 #define nf_bridge_pad(skb)			(0)
 #define br_drop_fake_rtable(skb)	        do { } while (0)
 #endif /* CONFIG_BRIDGE_NETFILTER */

net/bridge/br_forward.c

@@ -37,9 +37,7 @@ static inline int should_deliver(const struct net_bridge_port *p,
 
 int br_dev_queue_push_xmit(struct sk_buff *skb)
 {
-	/* ip_fragment doesn't copy the MAC header */
-	if (nf_bridge_maybe_copy_header(skb) ||
-	    !is_skb_forwardable(skb->dev, skb)) {
+	if (!is_skb_forwardable(skb->dev, skb)) {
 		kfree_skb(skb);
 	} else {
 		skb_push(skb, ETH_HLEN);

net/bridge/br_netfilter.c

@@ -764,6 +764,33 @@ static unsigned int br_nf_forward_arp(const struct nf_hook_ops *ops,
 }
 
 #if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
+static bool nf_bridge_copy_header(struct sk_buff *skb)
+{
+	int err;
+	unsigned int header_size;
+
+	nf_bridge_update_protocol(skb);
+	header_size = ETH_HLEN + nf_bridge_encap_header_len(skb);
+	err = skb_cow_head(skb, header_size);
+	if (err)
+		return false;
+
+	skb_copy_to_linear_data_offset(skb, -header_size,
+				       skb->nf_bridge->data, header_size);
+	__skb_push(skb, nf_bridge_encap_header_len(skb));
+	return true;
+}
+
+static int br_nf_push_frag_xmit(struct sk_buff *skb)
+{
+	if (!nf_bridge_copy_header(skb)) {
+		kfree_skb(skb);
+		return 0;
+	}
+
+	return br_dev_queue_push_xmit(skb);
+}
+
 static int br_nf_dev_queue_xmit(struct sk_buff *skb)
 {
 	int ret;
@@ -780,7 +807,7 @@ static int br_nf_dev_queue_xmit(struct sk_buff *skb)
 			/* Drop invalid packet */
 			return NF_DROP;
 		IPCB(skb)->frag_max_size = frag_max_size;
-		ret = ip_fragment(skb, br_dev_queue_push_xmit);
+		ret = ip_fragment(skb, br_nf_push_frag_xmit);
 	} else
 		ret = br_dev_queue_push_xmit(skb);