netfilter: conntrack: fix boot failure with nf_conntrack.enable_hooks=1

This is a revert of
7b1957b049 ("netfilter: nf_defrag_ipv4: use net_generic infra")
and a partial revert of
8b0adbe3e3 ("netfilter: nf_defrag_ipv6: use net_generic infra").

If conntrack is builtin and kernel is booted with:
nf_conntrack.enable_hooks=1

.... kernel will fail to boot due to a NULL deref in
nf_defrag_ipv4_enable(): Its called before the ipv4 defrag initcall is
made, so net_generic() returns NULL.

To resolve this, move the user refcount back to struct net so calls
to those functions are possible even before their initcalls have run.

Fixes: 7b1957b04956 ("netfilter: nf_defrag_ipv4: use net_generic infra")
Fixes: 8b0adbe3e38d ("netfilter: nf_defrag_ipv6: use net_generic infra").
Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/net/netfilter/ipv6/nf_defrag_ipv6.h

···
 struct nft_ct_frag6_pernet {
 	struct ctl_table_header *nf_frag_frags_hdr;
 	struct fqdir	*fqdir;
-	unsigned int users;
 };
 
 #endif /* _NF_DEFRAG_IPV6_H */

include/net/netns/netfilter.h

···
 #if IS_ENABLED(CONFIG_DECNET)
 	struct nf_hook_entries __rcu *hooks_decnet[NF_DN_NUMHOOKS];
 #endif
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
+	unsigned int defrag_ipv4_users;
+#endif
+#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
+	unsigned int defrag_ipv6_users;
+#endif
 };
 #endif

net/ipv4/netfilter/nf_defrag_ipv4.c

···
 #endif
 #include <net/netfilter/nf_conntrack_zones.h>
 
-static unsigned int defrag4_pernet_id __read_mostly;
 static DEFINE_MUTEX(defrag4_mutex);
-
-struct defrag4_pernet {
-	unsigned int users;
-};
 
 static int nf_ct_ipv4_gather_frags(struct net *net, struct sk_buff *skb,
 				   u_int32_t user)
···
 
 static void __net_exit defrag4_net_exit(struct net *net)
 {
-	struct defrag4_pernet *nf_defrag = net_generic(net, defrag4_pernet_id);
-
-	if (nf_defrag->users) {
+	if (net->nf.defrag_ipv4_users) {
 		nf_unregister_net_hooks(net, ipv4_defrag_ops,
 					ARRAY_SIZE(ipv4_defrag_ops));
-		nf_defrag->users = 0;
+		net->nf.defrag_ipv4_users = 0;
 	}
 }
 
 static struct pernet_operations defrag4_net_ops = {
 	.exit = defrag4_net_exit,
-	.id   = &defrag4_pernet_id,
-	.size = sizeof(struct defrag4_pernet),
 };
 
 static int __init nf_defrag_init(void)
···
 
 int nf_defrag_ipv4_enable(struct net *net)
 {
-	struct defrag4_pernet *nf_defrag = net_generic(net, defrag4_pernet_id);
 	int err = 0;
 
 	mutex_lock(&defrag4_mutex);
-	if (nf_defrag->users == UINT_MAX) {
+	if (net->nf.defrag_ipv4_users == UINT_MAX) {
 		err = -EOVERFLOW;
 		goto out_unlock;
 	}
 
-	if (nf_defrag->users) {
-		nf_defrag->users++;
+	if (net->nf.defrag_ipv4_users) {
+		net->nf.defrag_ipv4_users++;
 		goto out_unlock;
 	}
 
 	err = nf_register_net_hooks(net, ipv4_defrag_ops,
 				    ARRAY_SIZE(ipv4_defrag_ops));
 	if (err == 0)
-		nf_defrag->users = 1;
+		net->nf.defrag_ipv4_users = 1;
 
  out_unlock:
 	mutex_unlock(&defrag4_mutex);
···
 
 void nf_defrag_ipv4_disable(struct net *net)
 {
-	struct defrag4_pernet *nf_defrag = net_generic(net, defrag4_pernet_id);
-
 	mutex_lock(&defrag4_mutex);
-	if (nf_defrag->users) {
-		nf_defrag->users--;
-		if (nf_defrag->users == 0)
+	if (net->nf.defrag_ipv4_users) {
+		net->nf.defrag_ipv4_users--;
+		if (net->nf.defrag_ipv4_users == 0)
 			nf_unregister_net_hooks(net, ipv4_defrag_ops,
 						ARRAY_SIZE(ipv4_defrag_ops));
 	}

net/ipv6/netfilter/nf_conntrack_reasm.c

···
 
 static const char nf_frags_cache_name[] = "nf-frags";
 
-unsigned int nf_frag_pernet_id __read_mostly;
+static unsigned int nf_frag_pernet_id __read_mostly;
 static struct inet_frags nf_frags;
 
 static struct nft_ct_frag6_pernet *nf_frag_pernet(struct net *net)

net/ipv6/netfilter/nf_defrag_ipv6_hooks.c

···
 #include <net/netfilter/nf_conntrack_zones.h>
 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
 
-extern unsigned int nf_frag_pernet_id;
-
 static DEFINE_MUTEX(defrag6_mutex);
 
 static enum ip6_defrag_users nf_ct6_defrag_user(unsigned int hooknum,
···
 
 static void __net_exit defrag6_net_exit(struct net *net)
 {
-	struct nft_ct_frag6_pernet *nf_frag = net_generic(net, nf_frag_pernet_id);
-
-	if (nf_frag->users) {
+	if (net->nf.defrag_ipv6_users) {
 		nf_unregister_net_hooks(net, ipv6_defrag_ops,
 					ARRAY_SIZE(ipv6_defrag_ops));
-		nf_frag->users = 0;
+		net->nf.defrag_ipv6_users = 0;
 	}
 }
 
···
 
 int nf_defrag_ipv6_enable(struct net *net)
 {
-	struct nft_ct_frag6_pernet *nf_frag = net_generic(net, nf_frag_pernet_id);
 	int err = 0;
 
 	mutex_lock(&defrag6_mutex);
-	if (nf_frag->users == UINT_MAX) {
+	if (net->nf.defrag_ipv6_users == UINT_MAX) {
 		err = -EOVERFLOW;
 		goto out_unlock;
 	}
 
-	if (nf_frag->users) {
-		nf_frag->users++;
+	if (net->nf.defrag_ipv6_users) {
+		net->nf.defrag_ipv6_users++;
 		goto out_unlock;
 	}
 
 	err = nf_register_net_hooks(net, ipv6_defrag_ops,
 				    ARRAY_SIZE(ipv6_defrag_ops));
 	if (err == 0)
-		nf_frag->users = 1;
+		net->nf.defrag_ipv6_users = 1;
 
  out_unlock:
 	mutex_unlock(&defrag6_mutex);
···
 
 void nf_defrag_ipv6_disable(struct net *net)
 {
-	struct nft_ct_frag6_pernet *nf_frag = net_generic(net, nf_frag_pernet_id);
-
 	mutex_lock(&defrag6_mutex);
-	if (nf_frag->users) {
-		nf_frag->users--;
-		if (nf_frag->users == 0)
+	if (net->nf.defrag_ipv6_users) {
+		net->nf.defrag_ipv6_users--;
+		if (net->nf.defrag_ipv6_users == 0)
 			nf_unregister_net_hooks(net, ipv6_defrag_ops,
 						ARRAY_SIZE(ipv6_defrag_ops));
 	}