netfilter: Libify xt_TPROXY

The extracted functions will likely be usefull to implement tproxy
support in nf_tables.

Extrancted functions:
	- nf_tproxy_sk_is_transparent
	- nf_tproxy_laddr4
	- nf_tproxy_handle_time_wait4
	- nf_tproxy_get_sock_v4
	- nf_tproxy_laddr6
	- nf_tproxy_handle_time_wait6
	- nf_tproxy_get_sock_v6

(nf_)tproxy_handle_time_wait6 also needed some refactor as its current
implementation was xtables-specific.

Signed-off-by: Máté Eckl <ecklm94@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 151 insertions, 1 deletions

diff --git a/net/ipv6/netfilter/Kconfig b/net/ipv6/netfilter/Kconfig
index 9f5b00a39adf..37b14dc9d863 100644
--- a/net/ipv6/netfilter/Kconfig
+++ b/net/ipv6/netfilter/Kconfig
@@ -29,7 +29,10 @@ config NF_SOCKET_IPV6
 	tristate "IPv6 socket lookup support"
 	help
 	  This option enables the IPv6 socket lookup infrastructure. This
-	  is used by the ip6tables socket match.
+	  is used by the {ip6,nf}tables socket match.
+
+config NF_TPROXY_IPV6
+	tristate "IPv6 tproxy support"
 
 if NF_TABLES
 
diff --git a/net/ipv6/netfilter/Makefile b/net/ipv6/netfilter/Makefile
index 71518f22ae39..10a5a1c87320 100644
--- a/net/ipv6/netfilter/Makefile
+++ b/net/ipv6/netfilter/Makefile
@@ -26,6 +26,7 @@ nf_defrag_ipv6-y := nf_defrag_ipv6_hooks.o nf_conntrack_reasm.o
 obj-$(CONFIG_NF_DEFRAG_IPV6) += nf_defrag_ipv6.o
 
 obj-$(CONFIG_NF_SOCKET_IPV6) += nf_socket_ipv6.o
+obj-$(CONFIG_NF_TPROXY_IPV6) += nf_tproxy_ipv6.o
 
 # logging
 obj-$(CONFIG_NF_LOG_IPV6) += nf_log_ipv6.o
diff --git a/net/ipv6/netfilter/nf_tproxy_ipv6.c b/net/ipv6/netfilter/nf_tproxy_ipv6.c
new file mode 100644
index 000000000000..bf1d6c421e3b
--- /dev/null
+++ b/net/ipv6/netfilter/nf_tproxy_ipv6.c
@@ -0,0 +1,146 @@
+#include <net/netfilter/nf_tproxy.h>
+#include <linux/module.h>
+#include <net/inet6_hashtables.h>
+#include <net/addrconf.h>
+#include <net/udp.h>
+#include <net/tcp.h>
+
+const struct in6_addr *
+nf_tproxy_laddr6(struct sk_buff *skb, const struct in6_addr *user_laddr,
+	      const struct in6_addr *daddr)
+{
+	struct inet6_dev *indev;
+	struct inet6_ifaddr *ifa;
+	struct in6_addr *laddr;
+
+	if (!ipv6_addr_any(user_laddr))
+		return user_laddr;
+	laddr = NULL;
+
+	indev = __in6_dev_get(skb->dev);
+	if (indev) {
+		read_lock_bh(&indev->lock);
+		list_for_each_entry(ifa, &indev->addr_list, if_list) {
+			if (ifa->flags & (IFA_F_TENTATIVE | IFA_F_DEPRECATED))
+				continue;
+
+			laddr = &ifa->addr;
+			break;
+		}
+		read_unlock_bh(&indev->lock);
+	}
+
+	return laddr ? laddr : daddr;
+}
+EXPORT_SYMBOL_GPL(nf_tproxy_laddr6);
+
+struct sock *
+nf_tproxy_handle_time_wait6(struct sk_buff *skb, int tproto, int thoff,
+			 struct net *net,
+			 const struct in6_addr *laddr,
+			 const __be16 lport,
+			 struct sock *sk)
+{
+	const struct ipv6hdr *iph = ipv6_hdr(skb);
+	struct tcphdr _hdr, *hp;
+
+	hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
+	if (hp == NULL) {
+		inet_twsk_put(inet_twsk(sk));
+		return NULL;
+	}
+
+	if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
+		/* SYN to a TIME_WAIT socket, we'd rather redirect it
+		 * to a listener socket if there's one */
+		struct sock *sk2;
+
+		sk2 = nf_tproxy_get_sock_v6(net, skb, thoff, hp, tproto,
+					    &iph->saddr,
+					    nf_tproxy_laddr6(skb, laddr, &iph->daddr),
+					    hp->source,
+					    lport ? lport : hp->dest,
+					    skb->dev, NF_TPROXY_LOOKUP_LISTENER);
+		if (sk2) {
+			inet_twsk_deschedule_put(inet_twsk(sk));
+			sk = sk2;
+		}
+	}
+
+	return sk;
+}
+EXPORT_SYMBOL_GPL(nf_tproxy_handle_time_wait6);
+
+struct sock *
+nf_tproxy_get_sock_v6(struct net *net, struct sk_buff *skb, int thoff, void *hp,
+		      const u8 protocol,
+		      const struct in6_addr *saddr, const struct in6_addr *daddr,
+		      const __be16 sport, const __be16 dport,
+		      const struct net_device *in,
+		      const enum nf_tproxy_lookup_t lookup_type)
+{
+	struct sock *sk;
+	struct tcphdr *tcph;
+
+	switch (protocol) {
+	case IPPROTO_TCP:
+		switch (lookup_type) {
+		case NF_TPROXY_LOOKUP_LISTENER:
+			tcph = hp;
+			sk = inet6_lookup_listener(net, &tcp_hashinfo, skb,
+						   thoff + __tcp_hdrlen(tcph),
+						   saddr, sport,
+						   daddr, ntohs(dport),
+						   in->ifindex, 0);
+
+			if (sk && !refcount_inc_not_zero(&sk->sk_refcnt))
+				sk = NULL;
+			/* NOTE: we return listeners even if bound to
+			 * 0.0.0.0, those are filtered out in
+			 * xt_socket, since xt_TPROXY needs 0 bound
+			 * listeners too
+			 */
+			break;
+		case NF_TPROXY_LOOKUP_ESTABLISHED:
+			sk = __inet6_lookup_established(net, &tcp_hashinfo,
+							saddr, sport, daddr, ntohs(dport),
+							in->ifindex, 0);
+			break;
+		default:
+			BUG();
+		}
+		break;
+	case IPPROTO_UDP:
+		sk = udp6_lib_lookup(net, saddr, sport, daddr, dport,
+				     in->ifindex);
+		if (sk) {
+			int connected = (sk->sk_state == TCP_ESTABLISHED);
+			int wildcard = ipv6_addr_any(&sk->sk_v6_rcv_saddr);
+
+			/* NOTE: we return listeners even if bound to
+			 * 0.0.0.0, those are filtered out in
+			 * xt_socket, since xt_TPROXY needs 0 bound
+			 * listeners too
+			 */
+			if ((lookup_type == NF_TPROXY_LOOKUP_ESTABLISHED && (!connected || wildcard)) ||
+			    (lookup_type == NF_TPROXY_LOOKUP_LISTENER && connected)) {
+				sock_put(sk);
+				sk = NULL;
+			}
+		}
+		break;
+	default:
+		WARN_ON(1);
+		sk = NULL;
+	}
+
+	pr_debug("tproxy socket lookup: proto %u %pI6:%u -> %pI6:%u, lookup type: %d, sock %p\n",
+		 protocol, saddr, ntohs(sport), daddr, ntohs(dport), lookup_type, sk);
+
+	return sk;
+}
+EXPORT_SYMBOL_GPL(nf_tproxy_get_sock_v6);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
+MODULE_DESCRIPTION("Netfilter IPv4 transparent proxy support");