tests/netinet: add few tests for unconnected UDP socket

1) Test that getsockname() on a socket that experienced a sendto(2)
   returns allocated port.
2) Same as 1), but jailed.  Make sure IP address was also selected.
3) Test that IP_SENDSRCADDR/IP_RECVDSTADDR work.
4) Regression test for bug 274009.

tests/sys/netinet/Makefile

@@ -13,6 +13,7 @@ ATF_TESTS_C=	fibs_multibind_test \
 		tcp_connect_port_test \
 		tcp_implied_connect \
 		tcp_md5_getsockopt \
+		udp_bindings \
 		udp_io
 
 ATF_TESTS_SH=	arp \
@@ -29,6 +30,7 @@ ATF_TESTS_PYTEST+=	carp.py
 ATF_TESTS_PYTEST+=	igmp.py
 
 LIBADD.so_reuseport_lb_test=	pthread
+LIBADD.udp_bindings=		pthread
 
 # Some of the arp tests look for log messages in the dmesg buffer, so run them
 # serially to avoid problems with interleaved output.

tests/sys/netinet/udp_bindings.c

@@ -0,0 +1,249 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 Gleb Smirnoff <glebius@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/param.h>
+#include <sys/jail.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <errno.h>
+#include <ifaddrs.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <atf-c.h>
+
+static const char buf[] = "Hello";
+
+static void
+sendtolocalhost(int s)
+{
+	struct sockaddr_in dst = {
+		.sin_family = AF_INET,
+		.sin_len = sizeof(struct sockaddr_in),
+		.sin_addr = { htonl(INADDR_LOOPBACK) },
+		.sin_port = htons(1638),
+	};
+
+	ATF_REQUIRE(sendto(s, buf, sizeof(buf), 0, (struct sockaddr *)&dst,
+	    sizeof(dst)) == sizeof(buf));
+}
+
+/*
+ * Echo back to the sender its own address in payload.
+ */
+static void *
+echo(void *arg)
+{
+	int s = *(int *)arg;
+	struct sockaddr_in sin;
+	socklen_t slen = sizeof(sin);
+	char rbuf[sizeof(buf)];
+
+	ATF_REQUIRE(recvfrom(s, &rbuf, sizeof(rbuf), 0, (struct sockaddr *)&sin,
+	    &slen) == sizeof(rbuf));
+	printf("Echo to %s:%u\n", inet_ntoa(sin.sin_addr), ntohs(sin.sin_port));
+	ATF_REQUIRE(sendto(s, &sin, sizeof(sin), 0, (struct sockaddr *)&sin,
+	    sizeof(sin)) == sizeof(sin));
+	return (NULL);
+}
+
+/*
+ * Cycle through local addresses (normally there should be at least two
+ * different IPv4 ones), and communicate to the echo server checking both
+ * IP_SENDSRCADDR and IP_RECVDSTADDR.  Use same cmsg buffer for both send
+ * and receive operation, this is a suggested in manual, given that
+ * IP_RECVDSTADDR == IP_SENDSRCADDR.
+ * At the setup phase check that IP_SENDSRCADDR doesn't work on unbound socket.
+ */
+ATF_TC_WITHOUT_HEAD(IP_SENDSRCADDR);
+ATF_TC_BODY(IP_SENDSRCADDR, tc)
+{
+	struct sockaddr_in srv = {
+		.sin_family = AF_INET,
+		.sin_len = sizeof(struct sockaddr_in),
+	}, dst;
+	char cbuf[CMSG_SPACE(sizeof(struct in_addr))];
+	struct iovec iov = {
+		.iov_base = __DECONST(char *, buf),
+		.iov_len = sizeof(buf),
+	};
+	struct iovec riov = {
+		.iov_base = &dst,
+		.iov_len = sizeof(dst),
+	};
+	struct msghdr msg = {
+		.msg_iov = &iov,
+		.msg_iovlen = 1,
+		.msg_name = &srv,
+		.msg_namelen = sizeof(srv),
+		.msg_control = cbuf,
+		.msg_controllen = sizeof(cbuf),
+	};
+	struct msghdr rmsg = {
+		.msg_iov = &riov,
+		.msg_iovlen = 1,
+		.msg_control = cbuf,
+		.msg_controllen = sizeof(cbuf),
+	};
+	struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+	*cmsg = (struct cmsghdr) {
+		.cmsg_level = IPPROTO_IP,
+		.cmsg_type = IP_SENDSRCADDR,
+		.cmsg_len = CMSG_LEN(sizeof(struct in_addr)),
+	};
+	socklen_t slen = sizeof(struct sockaddr_in);
+	struct ifaddrs *ifa0, *ifa;
+	pthread_t tid;
+	int s, e;
+
+	/* First check that IP_SENDSRCADDR doesn't work on an unbound socket. */
+	ATF_REQUIRE((s = socket(PF_INET, SOCK_DGRAM, 0)) > 0);
+	ATF_REQUIRE_MSG(sendmsg(s, &msg, 0) == -1 && errno == EINVAL,
+	    "sendmsg(.cmsg_type = IP_SENDSRCADDR), errno %d", errno);
+
+	/* Bind to random ports both sender and echo server. */
+	ATF_REQUIRE(bind(s, (struct sockaddr *)&srv, sizeof(srv)) == 0);
+	ATF_REQUIRE((e = socket(PF_INET, SOCK_DGRAM, 0)) > 0);
+	ATF_REQUIRE(bind(e, (struct sockaddr *)&srv, sizeof(srv)) == 0);
+	ATF_REQUIRE(getsockname(e, (struct sockaddr *)&srv, &slen) == 0);
+	srv.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+
+	ATF_REQUIRE(getifaddrs(&ifa0) == 0);
+	for (ifa = ifa0; ifa != NULL; ifa = ifa->ifa_next) {
+		struct sockaddr_in src;
+		struct in_addr vrf;
+
+		if (ifa->ifa_addr->sa_family != AF_INET)
+			continue;
+		memcpy(&src, ifa->ifa_addr, sizeof(src));
+		printf("Sending from %s\n", inet_ntoa(src.sin_addr));
+		ATF_REQUIRE(pthread_create(&tid, NULL, echo, &e) == 0);
+		memcpy(CMSG_DATA(cmsg), &src.sin_addr, sizeof(src.sin_addr));
+		ATF_REQUIRE(sendmsg(s, &msg, 0) == sizeof(buf));
+		ATF_REQUIRE(recvmsg(s, &rmsg, 0) == sizeof(struct sockaddr_in));
+		memcpy(&vrf, CMSG_DATA(cmsg), sizeof(vrf));
+		ATF_REQUIRE_MSG(dst.sin_addr.s_addr == src.sin_addr.s_addr,
+		    "Sent from %s, but echo server reports %s",
+		    inet_ntoa(src.sin_addr), inet_ntoa(dst.sin_addr));
+		ATF_REQUIRE_MSG(vrf.s_addr == src.sin_addr.s_addr,
+		    "Sent from %s, but IP_RECVDSTADDR reports %s",
+		    inet_ntoa(src.sin_addr), inet_ntoa(vrf));
+		ATF_REQUIRE(pthread_join(tid, NULL) == 0);
+	}
+
+	freeifaddrs(ifa0);
+	close(s);
+	close(e);
+}
+
+/*
+ * Check gethostname(2) on a newborn socket, and then on an unconnected, but
+ * used socket.  The first shall return all-zeroes, and second one should
+ * return us our assigned port.
+ */
+ATF_TC_WITHOUT_HEAD(gethostname);
+ATF_TC_BODY(gethostname, tc)
+{
+	struct sockaddr_in sin;
+	socklen_t slen = sizeof(sin);
+	int s;
+
+	ATF_REQUIRE((s = socket(PF_INET, SOCK_DGRAM, 0)) > 0);
+	ATF_REQUIRE(getsockname(s, (struct sockaddr *)&sin, &slen) == 0);
+	ATF_REQUIRE_MSG(sin.sin_addr.s_addr == INADDR_ANY && sin.sin_port == 0,
+	    "newborn socket name %s:%u", inet_ntoa(sin.sin_addr),
+	    ntohs(sin.sin_port));
+	sendtolocalhost(s);
+	ATF_REQUIRE(getsockname(s, (struct sockaddr *)&sin, &slen) == 0);
+	ATF_REQUIRE_MSG(sin.sin_addr.s_addr == INADDR_ANY && sin.sin_port != 0,
+	    "used unconnected socket name %s:%u", inet_ntoa(sin.sin_addr),
+	    ntohs(sin.sin_port));
+	close(s);
+}
+
+ATF_TC_WITHOUT_HEAD(gethostname_jailed);
+ATF_TC_BODY(gethostname_jailed, tc)
+{
+	struct in_addr laddr = { htonl(INADDR_LOOPBACK) };
+	struct jail jconf = {
+		.version = JAIL_API_VERSION,
+		.path = __DECONST(char *, "/"),
+		.hostname = __DECONST(char *,"test"),
+		.ip4s = 1,
+		.ip4 = &laddr,
+	};
+	struct sockaddr_in sin;
+	socklen_t slen = sizeof(sin);
+	int s;
+
+	ATF_REQUIRE(jail(&jconf) > 0);
+	ATF_REQUIRE((s = socket(PF_INET, SOCK_DGRAM, 0)) > 0);
+	sendtolocalhost(s);
+	ATF_REQUIRE(getsockname(s, (struct sockaddr *)&sin, &slen) == 0);
+	ATF_REQUIRE_MSG(sin.sin_addr.s_addr == laddr.s_addr &&
+	    sin.sin_port != 0,
+	    "jailed unconnected socket name %s:%u", inet_ntoa(sin.sin_addr),
+	    ntohs(sin.sin_port));
+	close(s);
+}
+
+/*
+ * See bug 274009.
+ */
+ATF_TC_WITHOUT_HEAD(v4mapped);
+ATF_TC_BODY(v4mapped, tc)
+{
+	struct sockaddr_in6 sa6 = {
+		.sin6_family = AF_INET6,
+		.sin6_len = sizeof(struct sockaddr_in6),
+		.sin6_port = htons(1),
+	};
+	int s;
+
+	ATF_REQUIRE((s = socket(PF_INET6, SOCK_DGRAM, 0)) > 0);
+	ATF_REQUIRE(setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0},
+	    sizeof(int)) == 0);
+	ATF_REQUIRE(inet_pton(AF_INET6, "::ffff:127.0.0.1", &(sa6.sin6_addr))
+	    == 1);
+	ATF_REQUIRE(sendto(s, buf, sizeof(buf), 0, (struct sockaddr *)&sa6,
+	    sizeof(sa6)) == sizeof(buf));
+	close(s);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, v4mapped);
+	ATF_TP_ADD_TC(tp, gethostname);
+	ATF_TP_ADD_TC(tp, gethostname_jailed);
+	ATF_TP_ADD_TC(tp, IP_SENDSRCADDR);
+
+	return (atf_no_error());
+}