This patch reuses the framework already in place for sk_lookup, allowing
it now to send a reply from the server fd directly, instead of having to
create a socket bound to the original destination address and reply from
there. It does this by passing the source address and port from where to
reply from in a IP_ORIGDSTADDR ancillary message passed in sendmsg.

Signed-off-by: Tiago Lam <tiagolam@cloudflare.com>
---
 tools/testing/selftests/bpf/prog_tests/sk_lookup.c | 67 +++++++++++++++-------
 1 file changed, 45 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
index ae87c00867ba..df780624c16c 100644
--- a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
+++ b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
@@ -75,6 +75,7 @@ struct test {
 	struct inet_addr listen_at;
 	enum server accept_on;
 	bool reuseport_has_conns; /* Add a connected socket to reuseport group */
+	bool dont_bind_reply; /* Don't bind, send direct from server fd. */
 };
 
 struct cb_opts {
@@ -363,7 +364,7 @@ static void v4_to_v6(struct sockaddr_storage *ss)
 	memset(&v6->sin6_addr.s6_addr[0], 0, 10);
 }
 
-static int udp_recv_send(int server_fd)
+static int udp_recv_send(int server_fd, bool dont_bind_reply)
 {
 	char cmsg_buf[CMSG_SPACE(sizeof(struct sockaddr_storage))];
 	struct sockaddr_storage _src_addr = { 0 };
@@ -373,7 +374,7 @@ static int udp_recv_send(int server_fd)
 	struct iovec iov = { 0 };
 	struct cmsghdr *cm;
 	char buf[1];
-	int ret, fd;
+	int fd;
 	ssize_t n;
 
 	iov.iov_base = buf;
@@ -415,26 +416,37 @@ static int udp_recv_send(int server_fd)
 		v4_to_v6(dst_addr);
 	}
 
-	/* Reply from original destination address. */
-	fd = start_server_addr(SOCK_DGRAM, dst_addr, sizeof(*dst_addr), NULL);
-	if (!ASSERT_OK_FD(fd, "start_server_addr")) {
-		log_err("failed to create tx socket");
-		return -1;
-	}
+	if (dont_bind_reply) {
+		/* Reply directly from server fd, specifying the source address
+		 * and/or port in struct msghdr.
+		 */
+		n = sendmsg(server_fd, &msg, 0);
+		if (CHECK(n <= 0, "sendmsg", "failed\n")) {
+			log_err("failed to send echo reply");
+			return -1;
+		}
+	} else {
+		/* Reply from original destination address. */
+		fd = start_server_addr(SOCK_DGRAM, dst_addr, sizeof(*dst_addr),
+				       NULL);
+		if (!ASSERT_OK_FD(fd, "start_server_addr")) {
+			log_err("failed to create tx socket");
+			return -1;
+		}
 
-	msg.msg_control = NULL;
-	msg.msg_controllen = 0;
-	n = sendmsg(fd, &msg, 0);
-	if (CHECK(n <= 0, "sendmsg", "failed\n")) {
-		log_err("failed to send echo reply");
-		ret = -1;
-		goto out;
+		msg.msg_control = NULL;
+		msg.msg_controllen = 0;
+		n = sendmsg(fd, &msg, 0);
+		if (CHECK(n <= 0, "sendmsg", "failed\n")) {
+			log_err("failed to send echo reply");
+			close(fd);
+			return -1;
+		}
+
+		close(fd);
 	}
 
-	ret = 0;
-out:
-	close(fd);
-	return ret;
+	return 0;
 }
 
 static int tcp_echo_test(int client_fd, int server_fd)
@@ -454,14 +466,14 @@ static int tcp_echo_test(int client_fd, int server_fd)
 	return 0;
 }
 
-static int udp_echo_test(int client_fd, int server_fd)
+static int udp_echo_test(int client_fd, int server_fd, bool dont_bind_reply)
 {
 	int err;
 
 	err = send_byte(client_fd);
 	if (err)
 		return -1;
-	err = udp_recv_send(server_fd);
+	err = udp_recv_send(server_fd, dont_bind_reply);
 	if (err)
 		return -1;
 	err = recv_byte(client_fd);
@@ -653,7 +665,8 @@ static void run_lookup_prog(const struct test *t)
 	if (t->sotype == SOCK_STREAM)
 		tcp_echo_test(client_fd, server_fds[t->accept_on]);
 	else
-		udp_echo_test(client_fd, server_fds[t->accept_on]);
+		udp_echo_test(client_fd, server_fds[t->accept_on],
+			      t->dont_bind_reply);
 
 	close(client_fd);
 close:
@@ -775,6 +788,16 @@ static void test_redirect_lookup(struct test_sk_lookup *skel)
 			.listen_at	= { INT_IP4, INT_PORT },
 			.accept_on	= SERVER_B,
 		},
+		{
+			.desc		= "UDP IPv4 redir different ports",
+			.lookup_prog	= skel->progs.select_sock_a_no_reuseport,
+			.sock_map	= skel->maps.redir_map,
+			.sotype		= SOCK_DGRAM,
+			.connect_to	= { EXT_IP4, EXT_PORT },
+			.listen_at	= { INT_IP4, INT_PORT },
+			.accept_on	= SERVER_A,
+			.dont_bind_reply = true,
+		},
 		{
 			.desc		= "UDP IPv4 redir and reuseport with conns",
 			.lookup_prog	= skel->progs.select_sock_a,

-- 
2.34.1