netfilter: move checksum_partial indirection to struct nf_ipv6_ops

We cannot make a direct call to nf_ip6_checksum_partial() because that
would result in autoloading the 'ipv6' module because of symbol
dependencies.  Therefore, define checksum_partial indirection in
nf_ipv6_ops where this really belongs to.

For IPv4, we can indeed make a direct function call, which is faster,
given IPv4 is built-in in the networking code by default. Still,
CONFIG_INET=n and CONFIG_NETFILTER=y is possible, so define empty inline
stub for IPv4 in such case.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/bridge/netfilter/nf_tables_bridge.c b/net/bridge/netfilter/nf_tables_bridge.c
index b850c17..b24ac11 100644
--- a/net/bridge/netfilter/nf_tables_bridge.c
+++ b/net/bridge/netfilter/nf_tables_bridge.c
@@ -106,13 +106,6 @@ static int nf_br_reroute(struct net *net, struct sk_buff *skb,
 	return 0;
 }
 
-static __sum16 nf_br_checksum_partial(struct sk_buff *skb, unsigned int hook,
-				      unsigned int dataoff, unsigned int len,
-				      u_int8_t protocol)
-{
-	return 0;
-}
-
 static int nf_br_route(struct net *net, struct dst_entry **dst,
 		       struct flowi *fl, bool strict __always_unused)
 {
@@ -121,7 +114,6 @@ static int nf_br_route(struct net *net, struct dst_entry **dst,
 
 static const struct nf_afinfo nf_br_afinfo = {
 	.family                 = AF_BRIDGE,
-	.checksum_partial       = nf_br_checksum_partial,
 	.route                  = nf_br_route,
 	.saveroute              = nf_br_saveroute,
 	.reroute                = nf_br_reroute,
diff --git a/net/ipv4/netfilter.c b/net/ipv4/netfilter.c
index 2f7ffef..010c75f 100644
--- a/net/ipv4/netfilter.c
+++ b/net/ipv4/netfilter.c
@@ -155,9 +155,9 @@ __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 }
 EXPORT_SYMBOL(nf_ip_checksum);
 
-static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
-				      unsigned int dataoff, unsigned int len,
-				      u_int8_t protocol)
+__sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
+			       unsigned int dataoff, unsigned int len,
+			       u_int8_t protocol)
 {
 	const struct iphdr *iph = ip_hdr(skb);
 	__sum16 csum = 0;
@@ -175,6 +175,7 @@ static __sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 	}
 	return csum;
 }
+EXPORT_SYMBOL_GPL(nf_ip_checksum_partial);
 
 static int nf_ip_route(struct net *net, struct dst_entry **dst,
 		       struct flowi *fl, bool strict __always_unused)
@@ -188,7 +189,6 @@ static int nf_ip_route(struct net *net, struct dst_entry **dst,
 
 static const struct nf_afinfo nf_ip_afinfo = {
 	.family			= AF_INET,
-	.checksum_partial	= nf_ip_checksum_partial,
 	.route			= nf_ip_route,
 	.saveroute		= nf_ip_saveroute,
 	.reroute		= nf_ip_reroute,
diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index db69c8a..a57546c 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -190,15 +190,15 @@ static __sum16 nf_ip6_checksum_partial(struct sk_buff *skb, unsigned int hook,
 };
 
 static const struct nf_ipv6_ops ipv6ops = {
-	.chk_addr	= ipv6_chk_addr,
-	.route_input    = ip6_route_input,
-	.fragment	= ip6_fragment,
-	.checksum	= nf_ip6_checksum,
+	.chk_addr		= ipv6_chk_addr,
+	.route_input    	= ip6_route_input,
+	.fragment		= ip6_fragment,
+	.checksum		= nf_ip6_checksum,
+	.checksum_partial	= nf_ip6_checksum_partial,
 };
 
 static const struct nf_afinfo nf_ip6_afinfo = {
 	.family			= AF_INET6,
-	.checksum_partial	= nf_ip6_checksum_partial,
 	.route			= nf_ip6_route,
 	.saveroute		= nf_ip6_saveroute,
 	.reroute		= nf_ip6_reroute,
diff --git a/net/netfilter/utils.c b/net/netfilter/utils.c
index 159a9cd..ca6d8d6 100644
--- a/net/netfilter/utils.c
+++ b/net/netfilter/utils.c
@@ -24,3 +24,27 @@ __sum16 nf_checksum(struct sk_buff *skb, unsigned int hook,
 	return csum;
 }
 EXPORT_SYMBOL_GPL(nf_checksum);
+
+__sum16 nf_checksum_partial(struct sk_buff *skb, unsigned int hook,
+			    unsigned int dataoff, unsigned int len,
+			    u_int8_t protocol, unsigned short family)
+{
+	const struct nf_ipv6_ops *v6ops;
+	__sum16 csum = 0;
+
+	switch (family) {
+	case AF_INET:
+		csum = nf_ip_checksum_partial(skb, hook, dataoff, len,
+					      protocol);
+		break;
+	case AF_INET6:
+		v6ops = rcu_dereference(nf_ipv6_ops);
+		if (v6ops)
+			csum = v6ops->checksum_partial(skb, hook, dataoff, len,
+						       protocol);
+		break;
+	}
+
+	return csum;
+}
+EXPORT_SYMBOL_GPL(nf_checksum_partial);