netfilter: move checksum indirection to struct nf_ipv6_ops

We cannot make a direct call to nf_ip6_checksum() because that would
result in autoloading the 'ipv6' module because of symbol dependencies.
Therefore, define checksum 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

@@ -311,8 +311,6 @@ struct nf_queue_entry;
 
 struct nf_afinfo {
 	unsigned short	family;
-	__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,
@@ -333,20 +331,9 @@ static inline const struct nf_afinfo *nf_get_afinfo(unsigned short family)
 	return rcu_dereference(nf_afinfo[family]);
 }
 
-static inline __sum16
-nf_checksum(struct sk_buff *skb, unsigned int hook, unsigned int dataoff,
-	    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(skb, hook, dataoff, protocol);
-	rcu_read_unlock();
-	return csum;
-}
+__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,

include/linux/netfilter_ipv4.h

@@ -7,6 +7,16 @@
 #include <uapi/linux/netfilter_ipv4.h>
 
 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);
+#else
+static inline __sum16 nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
+				     unsigned int dataoff, u_int8_t protocol)
+{
+	return 0;
+}
+#endif /* CONFIG_INET */
+
 #endif /*__LINUX_IP_NETFILTER_H*/

include/linux/netfilter_ipv6.h

@@ -19,6 +19,8 @@ struct nf_ipv6_ops {
 	void (*route_input)(struct sk_buff *skb);
 	int (*fragment)(struct net *net, struct sock *sk, struct sk_buff *skb,
 			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);
 };
 
 #ifdef CONFIG_NETFILTER

net/bridge/netfilter/nf_tables_bridge.c

@@ -106,12 +106,6 @@ static int nf_br_reroute(struct net *net, struct sk_buff *skb,
 	return 0;
 }
 
-static __sum16 nf_br_checksum(struct sk_buff *skb, unsigned int hook,
-			      unsigned int dataoff, u_int8_t protocol)
-{
-	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)
@@ -127,7 +121,6 @@ static int nf_br_route(struct net *net, struct dst_entry **dst,
 
 static const struct nf_afinfo nf_br_afinfo = {
 	.family                 = AF_BRIDGE,
-	.checksum               = nf_br_checksum,
 	.checksum_partial       = nf_br_checksum_partial,
 	.route                  = nf_br_route,
 	.saveroute              = nf_br_saveroute,

net/ipv4/netfilter.c

@@ -188,7 +188,6 @@ static int nf_ip_route(struct net *net, struct dst_entry **dst,
 
 static const struct nf_afinfo nf_ip_afinfo = {
 	.family			= AF_INET,
-	.checksum		= nf_ip_checksum,
 	.checksum_partial	= nf_ip_checksum_partial,
 	.route			= nf_ip_route,
 	.saveroute		= nf_ip_saveroute,

net/ipv6/netfilter.c

@@ -192,12 +192,12 @@ 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
+	.fragment	= ip6_fragment,
+	.checksum	= nf_ip6_checksum,
 };
 
 static const struct nf_afinfo nf_ip6_afinfo = {
 	.family			= AF_INET6,
-	.checksum		= nf_ip6_checksum,
 	.checksum_partial	= nf_ip6_checksum_partial,
 	.route			= nf_ip6_route,
 	.saveroute		= nf_ip6_saveroute,

net/netfilter/Makefile

 # SPDX-License-Identifier: GPL-2.0
-netfilter-objs := core.o nf_log.o nf_queue.o nf_sockopt.o
+netfilter-objs := core.o nf_log.o nf_queue.o nf_sockopt.o utils.o
 
 nf_conntrack-y	:= nf_conntrack_core.o nf_conntrack_standalone.o nf_conntrack_expect.o nf_conntrack_helper.o nf_conntrack_proto.o nf_conntrack_l3proto_generic.o nf_conntrack_proto_generic.o nf_conntrack_proto_tcp.o nf_conntrack_proto_udp.o nf_conntrack_extend.o nf_conntrack_acct.o nf_conntrack_seqadj.o
 nf_conntrack-$(CONFIG_NF_CONNTRACK_TIMEOUT) += nf_conntrack_timeout.o

net/netfilter/utils.c

+#include <linux/kernel.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter_ipv4.h>
+#include <linux/netfilter_ipv6.h>
+
+__sum16 nf_checksum(struct sk_buff *skb, unsigned int hook,
+		    unsigned int dataoff, 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(skb, hook, dataoff, protocol);
+		break;
+	case AF_INET6:
+		v6ops = rcu_dereference(nf_ipv6_ops);
+		if (v6ops)
+			csum = v6ops->checksum(skb, hook, dataoff, protocol);
+		break;
+	}
+
+	return csum;
+}
+EXPORT_SYMBOL_GPL(nf_checksum);