tproxy: add lookup type checks for UDP in nf_tproxy_get_sock_v4()

Also, inline this function as the lookup_type is always a literal
and inlining removes branches performed at runtime.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
Signed-off-by: KOVACS Krisztian <hidden@balabit.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 114 insertions, 2 deletions

diff --git a/include/net/netfilter/nf_tproxy_core.h b/include/net/netfilter/nf_tproxy_core.h
index b3a8942a4e6a..1027d7f901a0 100644
--- a/include/net/netfilter/nf_tproxy_core.h
+++ b/include/net/netfilter/nf_tproxy_core.h
@@ -13,11 +13,123 @@
 #define NFT_LOOKUP_ESTABLISHED 2
 
 /* look up and get a reference to a matching socket */
-extern struct sock *
+
+
+/* This function is used by the 'TPROXY' target and the 'socket'
+ * match. The following lookups are supported:
+ *
+ * Explicit TProxy target rule
+ * ===========================
+ *
+ * This is used when the user wants to intercept a connection matching
+ * an explicit iptables rule. In this case the sockets are assumed
+ * matching in preference order:
+ *
+ *   - match: if there's a fully established connection matching the
+ *     _packet_ tuple, it is returned, assuming the redirection
+ *     already took place and we process a packet belonging to an
+ *     established connection
+ *
+ *   - match: if there's a listening socket matching the redirection
+ *     (e.g. on-port & on-ip of the connection), it is returned,
+ *     regardless if it was bound to 0.0.0.0 or an explicit
+ *     address. The reasoning is that if there's an explicit rule, it
+ *     does not really matter if the listener is bound to an interface
+ *     or to 0. The user already stated that he wants redirection
+ *     (since he added the rule).
+ *
+ * "socket" match based redirection (no specific rule)
+ * ===================================================
+ *
+ * There are connections with dynamic endpoints (e.g. FTP data
+ * connection) that the user is unable to add explicit rules
+ * for. These are taken care of by a generic "socket" rule. It is
+ * assumed that the proxy application is trusted to open such
+ * connections without explicit iptables rule (except of course the
+ * generic 'socket' rule). In this case the following sockets are
+ * matched in preference order:
+ *
+ *   - match: if there's a fully established connection matching the
+ *     _packet_ tuple
+ *
+ *   - match: if there's a non-zero bound listener (possibly with a
+ *     non-local address) We don't accept zero-bound listeners, since
+ *     then local services could intercept traffic going through the
+ *     box.
+ *
+ * Please note that there's an overlap between what a TPROXY target
+ * and a socket match will match. Normally if you have both rules the
+ * "socket" match will be the first one, effectively all packets
+ * belonging to established connections going through that one.
+ */
+static inline struct sock *
 nf_tproxy_get_sock_v4(struct net *net, const u8 protocol,
                       const __be32 saddr, const __be32 daddr,
                       const __be16 sport, const __be16 dport,
-                      const struct net_device *in, int lookup_type);
+                      const struct net_device *in, int lookup_type)
+{
+        struct sock *sk;
+
+        /* look up socket */
+        switch (protocol) {
+        case IPPROTO_TCP:
+                switch (lookup_type) {
+                case NFT_LOOKUP_ANY:
+                        sk = __inet_lookup(net, &tcp_hashinfo,
+                                           saddr, sport, daddr, dport,
+                                           in->ifindex);
+                        break;
+                case NFT_LOOKUP_LISTENER:
+                        sk = inet_lookup_listener(net, &tcp_hashinfo,
+                                                    daddr, dport,
+                                                    in->ifindex);
+
+                        /* 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 NFT_LOOKUP_ESTABLISHED:
+                        sk = inet_lookup_established(net, &tcp_hashinfo,
+                                                    saddr, sport, daddr, dport,
+                                                    in->ifindex);
+                        break;
+                default:
+                        WARN_ON(1);
+                        sk = NULL;
+                        break;
+                }
+                break;
+        case IPPROTO_UDP:
+                sk = udp4_lib_lookup(net, saddr, sport, daddr, dport,
+                                     in->ifindex);
+                if (sk && lookup_type != NFT_LOOKUP_ANY) {
+                        int connected = (sk->sk_state == TCP_ESTABLISHED);
+                        int wildcard = (inet_sk(sk)->inet_rcv_saddr == 0);
+
+                        /* 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 == NFT_LOOKUP_ESTABLISHED && (!connected || wildcard)) ||
+                            (lookup_type == NFT_LOOKUP_LISTENER && connected)) {
+                                sock_put(sk);
+                                sk = NULL;
+                        }
+                }
+                break;
+        default:
+                WARN_ON(1);
+                sk = NULL;
+        }
+
+        pr_debug("tproxy socket lookup: proto %u %08x:%u -> %08x:%u, lookup type: %d, sock %p\n",
+                 protocol, ntohl(saddr), ntohs(sport), ntohl(daddr), ntohs(dport), lookup_type, sk);
+
+        return sk;
+}
+
 
 static inline void
 nf_tproxy_put_sock(struct sock *sk)