netfilter: defrag: only register defrag functionality if needed

nf_defrag modules for ipv4 and ipv6 export an empty stub function.
Any module that needs the defragmentation hooks registered simply 'calls'
this empty function to create a phony module dependency -- modprobe will
then load the defrag module too.

This extends netfilter ipv4/ipv6 defragmentation modules to delay the hook
registration until the functionality is requested within a network namespace
instead of module load time for all namespaces.

Hooks are only un-registered on module unload or when a namespace that used
such defrag functionality exits.

We have to use struct net for this as the register hooks can be called
before netns initialization here from the ipv4/ipv6 conntrack module
init path.

There is no unregister functionality support, defrag will always be
active once it was requested inside a net namespace.

The reason is that defrag has impact on nft and iptables rulesets
(without defrag we might see framents).

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/net/netns/netfilter.h b/include/net/netns/netfilter.h
index 58487b1cc99a..cea396b53a60 100644
--- a/include/net/netns/netfilter.h
+++ b/include/net/netns/netfilter.h
@@ -17,5 +17,11 @@ struct netns_nf {
 	struct ctl_table_header *nf_log_dir_header;
 #endif
 	struct nf_hook_entry __rcu *hooks[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
+	bool			defrag_ipv4;
+#endif
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
+	bool			defrag_ipv6;
+#endif
 };
 #endif