netfilter: ipv6: add getsockopt to retrieve origdst

userspace can query the original ipv4 destination address of a REDIRECTed
connection via
getsockopt(m_sock, SOL_IP, SO_ORIGINAL_DST, &m_server_addr, &addrsize)

but for ipv6 no such option existed.

This adds getsockopt(..., IPPROTO_IPV6, IP6T_SO_ORIGINAL_DST, ...).

Without this, userspace needs to parse /proc or use ctnetlink, which
appears to be overkill.

This uses option number 80 for IP6T_SO_ORIGINAL_DST, which is spare,
to use the same number we use in the IPv4 socket option SO_ORIGINAL_DST.

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

1 files changed, 61 insertions, 0 deletions

diff --git a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
index 8860d23e61cf..02dcafdc7a95 100644
--- a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
+++ b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
@@ -21,6 +21,7 @@
 
 #include <linux/netfilter_bridge.h>
 #include <linux/netfilter_ipv6.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
 #include <net/netfilter/nf_conntrack.h>
 #include <net/netfilter/nf_conntrack_helper.h>
 #include <net/netfilter/nf_conntrack_l4proto.h>
@@ -295,6 +296,50 @@ static struct nf_hook_ops ipv6_conntrack_ops[] __read_mostly = {
         },
 };
 
+static int
+ipv6_getorigdst(struct sock *sk, int optval, void __user *user, int *len)
+{
+        const struct inet_sock *inet = inet_sk(sk);
+        const struct ipv6_pinfo *inet6 = inet6_sk(sk);
+        const struct nf_conntrack_tuple_hash *h;
+        struct sockaddr_in6 sin6;
+        struct nf_conntrack_tuple tuple = { .src.l3num = NFPROTO_IPV6 };
+        struct nf_conn *ct;
+
+        tuple.src.u3.in6 = inet6->rcv_saddr;
+        tuple.src.u.tcp.port = inet->inet_sport;
+        tuple.dst.u3.in6 = inet6->daddr;
+        tuple.dst.u.tcp.port = inet->inet_dport;
+        tuple.dst.protonum = sk->sk_protocol;
+
+        if (sk->sk_protocol != IPPROTO_TCP && sk->sk_protocol != IPPROTO_SCTP)
+                return -ENOPROTOOPT;
+
+        if (*len < 0 || (unsigned int) *len < sizeof(sin6))
+                return -EINVAL;
+
+        h = nf_conntrack_find_get(sock_net(sk), NF_CT_DEFAULT_ZONE, &tuple);
+        if (!h) {
+                pr_debug("IP6T_SO_ORIGINAL_DST: Can't find %pI6c/%u-%pI6c/%u.\n",
+                         &tuple.src.u3.ip6, ntohs(tuple.src.u.tcp.port),
+                         &tuple.dst.u3.ip6, ntohs(tuple.dst.u.tcp.port));
+                return -ENOENT;
+        }
+
+        ct = nf_ct_tuplehash_to_ctrack(h);
+
+        sin6.sin6_family = AF_INET6;
+        sin6.sin6_port = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.u.tcp.port;
+        sin6.sin6_flowinfo = inet6->flow_label & IPV6_FLOWINFO_MASK;
+        memcpy(&sin6.sin6_addr,
+                &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.u3.in6,
+                                        sizeof(sin6.sin6_addr));
+        sin6.sin6_scope_id = sk->sk_bound_dev_if;
+
+        nf_ct_put(ct);
+        return copy_to_user(user, &sin6, sizeof(sin6)) ? -EFAULT : 0;
+}
+
 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 
 #include <linux/netfilter/nfnetlink.h>
@@ -359,6 +404,14 @@ MODULE_ALIAS("nf_conntrack-" __stringify(AF_INET6));
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Yasuyuki KOZAKAI @USAGI <yasuyuki.kozakai@toshiba.co.jp>");
 
+static struct nf_sockopt_ops so_getorigdst6 = {
+        .pf             = NFPROTO_IPV6,
+        .get_optmin     = IP6T_SO_ORIGINAL_DST,
+        .get_optmax     = IP6T_SO_ORIGINAL_DST + 1,
+        .get            = ipv6_getorigdst,
+        .owner          = THIS_MODULE,
+};
+
 static int ipv6_net_init(struct net *net)
 {
         int ret = 0;
@@ -425,6 +478,12 @@ static int __init nf_conntrack_l3proto_ipv6_init(void)
         need_conntrack();
         nf_defrag_ipv6_enable();
 
+        ret = nf_register_sockopt(&so_getorigdst6);
+        if (ret < 0) {
+                pr_err("Unable to register netfilter socket option\n");
+                return ret;
+        }
+
         ret = register_pernet_subsys(&ipv6_net_ops);
         if (ret < 0)
                 goto cleanup_pernet;
@@ -440,6 +499,7 @@ static int __init nf_conntrack_l3proto_ipv6_init(void)
  cleanup_ipv6:
         unregister_pernet_subsys(&ipv6_net_ops);
  cleanup_pernet:
+        nf_unregister_sockopt(&so_getorigdst6);
         return ret;
 }
 
@@ -448,6 +508,7 @@ static void __exit nf_conntrack_l3proto_ipv6_fini(void)
         synchronize_net();
         nf_unregister_hooks(ipv6_conntrack_ops, ARRAY_SIZE(ipv6_conntrack_ops));
         unregister_pernet_subsys(&ipv6_net_ops);
+        nf_unregister_sockopt(&so_getorigdst6);
 }
 
 module_init(nf_conntrack_l3proto_ipv6_init);