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>

include/linux/netfilter.h

@@ -311,11 +311,6 @@ struct nf_queue_entry;
 
 struct nf_afinfo {
 	unsigned short	family;
-	__sum16		(*checksum_partial)(struct sk_buff *skb,
-					    unsigned int hook,
-					    unsigned int dataoff,
-					    unsigned int len,
-					    u_int8_t protocol);
 	int		(*route)(struct net *net, struct dst_entry **dst,
 				 struct flowi *fl, bool strict);
 	void		(*saveroute)(const struct sk_buff *skb,
@@ -335,22 +330,9 @@ __sum16 nf_checksum(struct sk_buff *skb, unsigned int hook,
 		    unsigned int dataoff, u_int8_t protocol,
 		    unsigned short family);
 
-static inline __sum16
-nf_checksum_partial(struct sk_buff *skb, unsigned int hook,
+__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_afinfo *afinfo;
-	__sum16 csum = 0;
-
-	rcu_read_lock();
-	afinfo = nf_get_afinfo(family);
-	if (afinfo)
-		csum = afinfo->checksum_partial(skb, hook, dataoff, len,
-						protocol);
-	rcu_read_unlock();
-	return csum;
-}
+			    u_int8_t protocol, unsigned short family);
 
 int nf_register_afinfo(const struct nf_afinfo *afinfo);
 void nf_unregister_afinfo(const struct nf_afinfo *afinfo);

include/linux/netfilter_ipv4.h

@@ -11,12 +11,23 @@ int ip_route_me_harder(struct net *net, struct sk_buff *skb, unsigned addr_type)
 #ifdef CONFIG_INET
 __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 		       unsigned int dataoff, 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);
 #else
 static inline __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
 				     unsigned int dataoff, u_int8_t protocol)
 {
 	return 0;
 }
+static inline __sum16 nf_ip_checksum_partial(struct sk_buff *skb,
+					     unsigned int hook,
+					     unsigned int dataoff,
+					     unsigned int len,
+					     u_int8_t protocol)
+{
+	return 0;
+}
 #endif /* CONFIG_INET */
 
 #endif /*__LINUX_IP_NETFILTER_H*/

include/linux/netfilter_ipv6.h

@@ -21,6 +21,9 @@ struct nf_ipv6_ops {
 			int (*output)(struct net *, struct sock *, struct sk_buff *));
 	__sum16 (*checksum)(struct sk_buff *skb, unsigned int hook,
 			    unsigned int dataoff, u_int8_t protocol);
+	__sum16 (*checksum_partial)(struct sk_buff *skb, unsigned int hook,
+				    unsigned int dataoff, unsigned int len,
+				    u_int8_t protocol);
 };
 
 #ifdef CONFIG_NETFILTER

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,

net/ipv4/netfilter.c

@@ -155,7 +155,7 @@ __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,
+__sum16 nf_ip_checksum_partial(struct sk_buff *skb, unsigned int hook,
 			       unsigned int dataoff, unsigned int len,
 			       u_int8_t protocol)
 {
@@ -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,

net/ipv6/netfilter.c

@@ -194,11 +194,11 @@ static const struct nf_ipv6_ops ipv6ops = {
 	.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,

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);