netfilter: avoid ipv6 -> nf_defrag_ipv6 module dependency

nf_ct_frag6_gather is part of nf_defrag_ipv6.ko, not ipv6 core.

The current use of the netfilter ipv6 stub indirections  causes a module
dependency between ipv6 and nf_defrag_ipv6.

This prevents nf_defrag_ipv6 module from being removed because ipv6 can't
be unloaded.

Remove the indirection and always use a direct call.  This creates a
depency from nf_conntrack_bridge to nf_defrag_ipv6 instead:

modinfo nf_conntrack
depends:        nf_conntrack,nf_defrag_ipv6,bridge

.. and nf_conntrack already depends on nf_defrag_ipv6 anyway.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter_ipv6.h

@@ -58,7 +58,6 @@ struct nf_ipv6_ops {
 			int (*output)(struct net *, struct sock *, struct sk_buff *));
 	int (*reroute)(struct sk_buff *skb, const struct nf_queue_entry *entry);
 #if IS_MODULE(CONFIG_IPV6)
-	int (*br_defrag)(struct net *net, struct sk_buff *skb, u32 user);
 	int (*br_fragment)(struct net *net, struct sock *sk,
 			   struct sk_buff *skb,
 			   struct nf_bridge_frag_data *data,
@@ -117,23 +116,6 @@ static inline int nf_ip6_route(struct net *net, struct dst_entry **dst,
 
 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
 
-static inline int nf_ipv6_br_defrag(struct net *net, struct sk_buff *skb,
-				    u32 user)
-{
-#if IS_MODULE(CONFIG_IPV6)
-	const struct nf_ipv6_ops *v6_ops = nf_get_ipv6_ops();
-
-	if (!v6_ops)
-		return 1;
-
-	return v6_ops->br_defrag(net, skb, user);
-#elif IS_BUILTIN(CONFIG_IPV6)
-	return nf_ct_frag6_gather(net, skb, user);
-#else
-	return 1;
-#endif
-}
-
 int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		    struct nf_bridge_frag_data *data,
 		    int (*output)(struct net *, struct sock *sk,

net/bridge/netfilter/nf_conntrack_bridge.c

@@ -168,6 +168,7 @@ static unsigned int nf_ct_br_defrag4(struct sk_buff *skb,
 static unsigned int nf_ct_br_defrag6(struct sk_buff *skb,
 				     const struct nf_hook_state *state)
 {
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
 	u16 zone_id = NF_CT_DEFAULT_ZONE_ID;
 	enum ip_conntrack_info ctinfo;
 	struct br_input_skb_cb cb;
@@ -180,7 +181,7 @@ static unsigned int nf_ct_br_defrag6(struct sk_buff *skb,
 
 	br_skb_cb_save(skb, &cb, sizeof(struct inet6_skb_parm));
 
-	err = nf_ipv6_br_defrag(state->net, skb,
+	err = nf_ct_frag6_gather(state->net, skb,
 				 IP_DEFRAG_CONNTRACK_BRIDGE_IN + zone_id);
 	/* queued */
 	if (err == -EINPROGRESS)
@@ -188,6 +189,9 @@ static unsigned int nf_ct_br_defrag6(struct sk_buff *skb,
 
 	br_skb_cb_restore(skb, &cb, IP6CB(skb)->frag_max_size);
 	return err == 0 ? NF_ACCEPT : NF_DROP;
+#else
+	return NF_ACCEPT;
+#endif
 }
 
 static int nf_ct_br_ip_check(const struct sk_buff *skb)

net/ipv6/netfilter.c

@@ -245,9 +245,6 @@ static const struct nf_ipv6_ops ipv6ops = {
 	.route_input		= ip6_route_input,
 	.fragment		= ip6_fragment,
 	.reroute		= nf_ip6_reroute,
-#if IS_MODULE(CONFIG_IPV6) && IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
-	.br_defrag		= nf_ct_frag6_gather,
-#endif
 #if IS_MODULE(CONFIG_IPV6)
 	.br_fragment		= br_ip6_fragment,
 #endif