tests/netinet: add few tests for sending a broadcast packet

1) Set SO_BROADCAST and send to INADDR_BROADCAST.
2) Set SO_BROADCAST, set IP_ONESBCAST and cycle through broadcast capable
   interfaces sending a datagram on each.
3) Set SO_BROADCAST and send to local broadcast address.

For each test we bind a second socket to check whether the broadcast
is actually received.

Reviewed by:		markj
Differential Revision:	https://reviews.freebsd.org/D49040

tests/sys/netinet/Makefile

@@ -5,7 +5,8 @@ BINDIR=		${TESTSDIR}
 
 TESTS_SUBDIRS+=	libalias
 
-ATF_TESTS_C=	fibs_multibind_test \
+ATF_TESTS_C=	broadcast \
+		fibs_multibind_test \
 		ip_reass_test \
 		ip6_v4mapped_test \
 		so_reuseport_lb_test \

tests/sys/netinet/broadcast.c

@@ -0,0 +1,192 @@
+/*-
+ * 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/socket.h>
+#include <netinet/in.h>
+#include <net/if.h>
+#include <arpa/inet.h>
+#include <errno.h>
+#include <ifaddrs.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <atf-c.h>
+
+static const char buf[] = "Hello";
+
+/* Create a UDP socket with SO_BROADCAST set. */
+static int
+bcastsock(void)
+{
+	int s;
+
+	ATF_REQUIRE((s = socket(PF_INET, SOCK_DGRAM, 0)) > 0);
+	ATF_REQUIRE(setsockopt(s, SOL_SOCKET, SO_BROADCAST, &(int){1},
+	    sizeof(int)) == 0);
+	return (s);
+}
+
+/* Send on socket 's' with address 'to', confirm receive on 'r'. */
+static void
+bcastecho(int s, struct sockaddr_in *to, int r)
+{
+	char rbuf[sizeof(buf)];
+
+	printf("Sending to %s\n", inet_ntoa(to->sin_addr));
+	ATF_REQUIRE_MSG(sendto(s, buf, sizeof(buf), 0, (struct sockaddr *)to,
+	    sizeof(*to)) == sizeof(buf), "sending of broadcast failed: %d",
+	    errno);
+	ATF_REQUIRE(recv(r, rbuf, sizeof(rbuf), 0) == sizeof(rbuf));
+	ATF_REQUIRE_MSG(memcmp(buf, rbuf, sizeof(buf)) == 0,
+	    "failed to receive own broadcast");
+}
+
+/* Find a first broadcast capable interface and copy its broadcast address. */
+static void
+firstbcast(struct in_addr *out)
+{
+	struct ifaddrs *ifa0, *ifa;
+	struct sockaddr_in sin;
+
+	ATF_REQUIRE(getifaddrs(&ifa0) == 0);
+	for (ifa = ifa0; ifa != NULL; ifa = ifa->ifa_next)
+		if (ifa->ifa_addr->sa_family == AF_INET &&
+		    (ifa->ifa_flags & IFF_BROADCAST))
+			break;
+	if (ifa == NULL) {
+		freeifaddrs(ifa0);
+		atf_tc_skip("No broadcast address found");
+	}
+	memcpy(&sin, ifa->ifa_broadaddr, sizeof(struct sockaddr_in));
+	*out = sin.sin_addr;
+	freeifaddrs(ifa0);
+}
+
+/* Application sends to INADDR_BROADCAST, and this goes on the wire. */
+ATF_TC_WITHOUT_HEAD(INADDR_BROADCAST);
+ATF_TC_BODY(INADDR_BROADCAST, tc)
+{
+	struct sockaddr_in sin = {
+		.sin_family = AF_INET,
+		.sin_len = sizeof(struct sockaddr_in),
+	};
+	socklen_t slen = sizeof(sin);
+	int l, s;
+
+	l = bcastsock();
+	ATF_REQUIRE(bind(l, (struct sockaddr *)&sin, sizeof(sin)) == 0);
+	ATF_REQUIRE(getsockname(l, (struct sockaddr *)&sin, &slen) == 0);
+	sin.sin_addr.s_addr = htonl(INADDR_BROADCAST);
+
+	s = bcastsock();
+	bcastecho(s, &sin, l);
+
+	close(s);
+	close(l);
+}
+
+/*
+ * Application sends on broadcast address of an interface, INADDR_BROADCAST
+ * goes on the wire of the selected interface.
+ */
+ATF_TC_WITHOUT_HEAD(IP_ONESBCAST);
+ATF_TC_BODY(IP_ONESBCAST, tc)
+{
+	struct ifaddrs *ifa0, *ifa;
+	struct sockaddr_in sin = {
+		.sin_family = AF_INET,
+		.sin_len = sizeof(struct sockaddr_in),
+	};
+	socklen_t slen = sizeof(sin);
+	int s, l;
+	in_port_t port;
+	bool skip = true;
+
+	s = bcastsock();
+	ATF_REQUIRE(setsockopt(s, IPPROTO_IP, IP_ONESBCAST, &(int){1},
+	    sizeof(int)) == 0);
+
+	l = bcastsock();
+	ATF_REQUIRE(bind(l, (struct sockaddr *)&sin, sizeof(sin)) == 0);
+	ATF_REQUIRE(getsockname(l, (struct sockaddr *)&sin, &slen) == 0);
+	port = sin.sin_port;
+
+	ATF_REQUIRE(getifaddrs(&ifa0) == 0);
+	for (ifa = ifa0; ifa != NULL; ifa = ifa->ifa_next) {
+		if (ifa->ifa_addr->sa_family != AF_INET)
+			continue;
+		if (!(ifa->ifa_flags & IFF_BROADCAST))
+			continue;
+		skip = false;
+		memcpy(&sin, ifa->ifa_broadaddr, sizeof(struct sockaddr_in));
+		sin.sin_port = port;
+		bcastecho(s, &sin, l);
+	}
+	freeifaddrs(ifa0);
+	close(s);
+	close(l);
+	if (skip)
+		atf_tc_skip("No broadcast address found");
+}
+
+/*
+ * Application sends on broadcast address of an interface, and this is what
+ * goes out the wire.
+ */
+ATF_TC_WITHOUT_HEAD(local_broadcast);
+ATF_TC_BODY(local_broadcast, tc)
+{
+	struct sockaddr_in sin = {
+		.sin_family = AF_INET,
+		.sin_len = sizeof(struct sockaddr_in),
+	};
+	socklen_t slen = sizeof(sin);
+	int s, l;
+
+	s = bcastsock();
+	l = bcastsock();
+	ATF_REQUIRE(bind(l, (struct sockaddr *)&sin, sizeof(sin)) == 0);
+	ATF_REQUIRE(getsockname(l, (struct sockaddr *)&sin, &slen) == 0);
+	firstbcast(&sin.sin_addr);
+
+	bcastecho(s, &sin, l);
+
+	close(s);
+	close(l);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, INADDR_BROADCAST);
+	ATF_TP_ADD_TC(tp, IP_ONESBCAST);
+	ATF_TP_ADD_TC(tp, local_broadcast);
+
+	return (atf_no_error());
+}