ifconfig: Exit with a non-zero status when SIOCSIFFIB fails

Previously, setting an interface FIB to some invalid value would result
in a warning being printed, but the ifconfig command would exit with
status 0, but this is wrong.

Add a little regression test.

Reviewed by:	pouria, zlei, melifaro
MFC after:	2 weeks
Sponsored by:	Stormshield
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D54918

sbin/ifconfig/iffib.c

@@ -69,14 +69,12 @@ setiffib(if_ctx *ctx, const char *val, int dummy __unused)
 	char *ep;
 
 	fib = strtoul(val, &ep, 0);
-	if (*ep != '\0' || fib > UINT_MAX) {
-		warn("fib %s not valid", val);
-		return;
-	}
+	if (*ep != '\0' || fib > UINT_MAX)
+		errx(1, "fib %s not valid", val);
 
 	ifr.ifr_fib = fib;
 	if (ioctl_ctx_ifr(ctx, SIOCSIFFIB, &ifr) < 0)
-		warn("ioctl (SIOCSIFFIB)");
+		err(1, "ioctl (SIOCSIFFIB)");
 }
 
 static void
@@ -87,14 +85,12 @@ settunfib(if_ctx *ctx, const char *val, int dummy __unused)
 	char *ep;
 
 	fib = strtoul(val, &ep, 0);
-	if (*ep != '\0' || fib > UINT_MAX) {
-		warn("fib %s not valid", val);
-		return;
-	}
+	if (*ep != '\0' || fib > UINT_MAX)
+		errx(1, "fib %s not valid", val);
 
 	ifr.ifr_fib = fib;
 	if (ioctl_ctx_ifr(ctx, SIOCSTUNFIB, &ifr) < 0)
-		warn("ioctl (SIOCSTUNFIB)");
+		err(1, "ioctl (SIOCSTUNFIB)");
 }
 
 static struct cmd fib_cmds[] = {

sbin/ifconfig/tests/Makefile

@@ -1,5 +1,6 @@
 NETBSD_ATF_TESTS_SH=	nonexistent_test
-ATF_TESTS_SH+=		inet6
+ATF_TESTS_SH+=		ifconfig \
+			inet6
 
 TEST_METADATA+=	execenv="jail"
 TEST_METADATA+=	execenv_jail_params="vnet allow.raw_sockets"

sbin/ifconfig/tests/ifconfig.sh

@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (c) 2026 Stormshield
+
+. $(atf_get_srcdir)/../../sys/common/vnet.subr
+
+atf_test_case "badfib" "cleanup"
+badfib_head()
+{
+	atf_set descr "Test adding an interface to a non-existent FIB"
+	atf_set require.user root
+}
+badfib_body()
+{
+	local epair
+
+	vnet_init
+
+	epair=$(vnet_mkepair)
+	atf_check -s exit:0 ifconfig ${epair}a fib 0
+	atf_check -s not-exit:0 -e not-empty \
+	    ifconfig ${epair}a fib $(sysctl -n net.fibs)
+}
+badfib_cleanup()
+{
+	vnet_cleanup
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case badfib
+}