selftests/bpf: Test BPF socket lookup and reuseport with connections

Cover the case when BPF socket lookup returns a socket that belongs to a
reuseport group, and the reuseport group contains connected UDP sockets.

Ensure that the presence of connected UDP sockets in reuseport group does
not affect the socket lookup result. Socket selected by reuseport should
always be used as result in such case.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Link: https://lore.kernel.org/bpf/20200722161720.940831-3-jakub@cloudflare.com

tools/testing/selftests/bpf/prog_tests/sk_lookup.c

@@ -74,6 +74,7 @@ struct test {
 	struct inet_addr connect_to;
 	struct inet_addr listen_at;
 	enum server accept_on;
+	bool reuseport_has_conns; /* Add a connected socket to reuseport group */
 };
 
 static __u32 duration;		/* for CHECK macro */
@@ -559,7 +560,8 @@ static void query_lookup_prog(struct test_sk_lookup *skel)
 
 static void run_lookup_prog(const struct test *t)
 {
-	int client_fd, server_fds[MAX_SERVERS] = { -1 };
+	int server_fds[MAX_SERVERS] = { -1 };
+	int client_fd, reuse_conn_fd = -1;
 	struct bpf_link *lookup_link;
 	int i, err;
 
@@ -583,6 +585,32 @@ static void run_lookup_prog(const struct test *t)
 			break;
 	}
 
+	/* Regular UDP socket lookup with reuseport behaves
+	 * differently when reuseport group contains connected
+	 * sockets. Check that adding a connected UDP socket to the
+	 * reuseport group does not affect how reuseport works with
+	 * BPF socket lookup.
+	 */
+	if (t->reuseport_has_conns) {
+		struct sockaddr_storage addr = {};
+		socklen_t len = sizeof(addr);
+
+		/* Add an extra socket to reuseport group */
+		reuse_conn_fd = make_server(t->sotype, t->listen_at.ip,
+					    t->listen_at.port,
+					    t->reuseport_prog);
+		if (reuse_conn_fd < 0)
+			goto close;
+
+		/* Connect the extra socket to itself */
+		err = getsockname(reuse_conn_fd, (void *)&addr, &len);
+		if (CHECK(err, "getsockname", "errno %d\n", errno))
+			goto close;
+		err = connect(reuse_conn_fd, (void *)&addr, len);
+		if (CHECK(err, "connect", "errno %d\n", errno))
+			goto close;
+	}
+
 	client_fd = make_client(t->sotype, t->connect_to.ip, t->connect_to.port);
 	if (client_fd < 0)
 		goto close;
@@ -594,6 +622,8 @@ static void run_lookup_prog(const struct test *t)
 
 	close(client_fd);
 close:
+	if (reuse_conn_fd != -1)
+		close(reuse_conn_fd);
 	for (i = 0; i < ARRAY_SIZE(server_fds); i++) {
 		if (server_fds[i] != -1)
 			close(server_fds[i]);
@@ -710,6 +740,17 @@ static void test_redirect_lookup(struct test_sk_lookup *skel)
 			.listen_at	= { INT_IP4, INT_PORT },
 			.accept_on	= SERVER_B,
 		},
+		{
+			.desc		= "UDP IPv4 redir and reuseport with conns",
+			.lookup_prog	= skel->progs.select_sock_a,
+			.reuseport_prog	= skel->progs.select_sock_b,
+			.sock_map	= skel->maps.redir_map,
+			.sotype		= SOCK_DGRAM,
+			.connect_to	= { EXT_IP4, EXT_PORT },
+			.listen_at	= { INT_IP4, INT_PORT },
+			.accept_on	= SERVER_B,
+			.reuseport_has_conns = true,
+		},
 		{
 			.desc		= "UDP IPv4 redir skip reuseport",
 			.lookup_prog	= skel->progs.select_sock_a_no_reuseport,
@@ -754,6 +795,17 @@ static void test_redirect_lookup(struct test_sk_lookup *skel)
 			.listen_at	= { INT_IP6, INT_PORT },
 			.accept_on	= SERVER_B,
 		},
+		{
+			.desc		= "UDP IPv6 redir and reuseport with conns",
+			.lookup_prog	= skel->progs.select_sock_a,
+			.reuseport_prog	= skel->progs.select_sock_b,
+			.sock_map	= skel->maps.redir_map,
+			.sotype		= SOCK_DGRAM,
+			.connect_to	= { EXT_IP6, EXT_PORT },
+			.listen_at	= { INT_IP6, INT_PORT },
+			.accept_on	= SERVER_B,
+			.reuseport_has_conns = true,
+		},
 		{
 			.desc		= "UDP IPv6 redir skip reuseport",
 			.lookup_prog	= skel->progs.select_sock_a_no_reuseport,