netinet: handle blackhole routes

If during ip_forward() we find a blackhole (or reject) route we should stop
processing and count this in the 'cantforward' counter, just like we already do
for IPv6.
Blackhole routes are set to use the loopback interface, so we don't actually
incorrectly forward traffic, but we do fail to count it as unroutable.

Test this, both for IPv4 and IPv6.

Reviewed by:	melifaro
Sponsored by:	Rubicon Communications, LLC ("Netgate")
Differential Revision:	https://reviews.freebsd.org/D47529

sys/netinet/ip_input.c

@@ -942,6 +942,18 @@ ip_forward(struct mbuf *m, int srcrt)
 	flowid = m->m_pkthdr.flowid;
 	ro.ro_nh = fib4_lookup(M_GETFIB(m), ip->ip_dst, 0, NHR_REF, flowid);
 	if (ro.ro_nh != NULL) {
+		if (ro.ro_nh->nh_flags & (NHF_BLACKHOLE | NHF_BROADCAST)) {
+			IPSTAT_INC(ips_cantforward);
+			m_freem(m);
+			NH_FREE(ro.ro_nh);
+			return;
+		}
+		if (ro.ro_nh->nh_flags & NHF_REJECT) {
+			IPSTAT_INC(ips_cantforward);
+			NH_FREE(ro.ro_nh);
+			icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, 0, 0);
+			return;
+		}
 		ia = ifatoia(ro.ro_nh->nh_ifa);
 	} else
 		ia = NULL;

tests/sys/netinet/forward.sh

@@ -259,6 +259,58 @@ fwd_ip_icmp_gw_slow_success_cleanup() {
 	vnet_cleanup
 }
 
+atf_test_case "fwd_ip_blackhole" "cleanup"
+fwd_ip_blackhole_head() {
+
+	atf_set descr 'Test blackhole routes'
+	atf_set require.user root
+}
+
+fwd_ip_blackhole_body() {
+	jname="v4t-fwd_ip_blackhole"
+
+	vnet_init
+
+	epair=$(vnet_mkepair)
+	epair_out=$(vnet_mkepair)
+
+	ifconfig ${epair}a 192.0.2.2/24 up
+
+	vnet_mkjail ${jname} ${epair}b ${epair_out}b
+	jexec ${jname} ifconfig lo0 127.0.0.1/8 up
+	jexec ${jname} ifconfig ${epair}b 192.0.2.1/24 up
+	jexec ${jname} ifconfig ${epair_out}b 198.51.100.1/24 up
+	jexec ${jname} sysctl net.inet.ip.forwarding=1
+
+	route add default 192.0.2.1
+
+	atf_check -s exit:2 -o ignore \
+	    ping -c 1 -t 1 198.51.100.2
+	atf_check -s exit:0 -o match:"0 packets not forwardable" \
+	    jexec ${jname} netstat -s -p ip
+
+	# Create blackhole route
+	jexec ${jname} /sbin/route add 198.51.100.2 -blackhole -fib 0
+	jexec ${jname} netstat -rn
+
+	# Include an IP option to ensure slow path
+	atf_check -s exit:2 -o ignore \
+	    ping -c 1 -t 1 -R 198.51.100.2
+	atf_check -s exit:0 -o match:"1 packet not forwardable" \
+	    jexec ${jname} netstat -s -p ip
+
+	# Now try via the fast path
+	atf_check -s exit:2 -o ignore \
+	    ping -c 1 -t 1 198.51.100.2
+	atf_check -s exit:0 -o match:"2 packets not forwardable" \
+	    jexec ${jname} netstat -s -p ip
+}
+
+fwd_ip_blackhole_cleanup() {
+
+	vnet_cleanup
+}
+
 atf_init_test_cases()
 {
 
@@ -266,6 +318,7 @@ atf_init_test_cases()
 	atf_add_test_case "fwd_ip_icmp_gw_fast_success"
 	atf_add_test_case "fwd_ip_icmp_iface_slow_success"
 	atf_add_test_case "fwd_ip_icmp_gw_slow_success"
+	atf_add_test_case "fwd_ip_blackhole"
 }
 
 # end

tests/sys/netinet6/forward6.sh

@@ -466,6 +466,59 @@ fwd_ip6_gu_icmp_gw_ll_slow_success_cleanup() {
 	vnet_cleanup
 }
 
+atf_test_case "fwd_ip6_blackhole" "cleanup"
+fwd_ip6_blackhole_head() {
+
+	atf_set descr 'Test blackhole routing'
+	atf_set require.user root
+}
+
+fwd_ip6_blackhole_body() {
+	jname="v6t-fwd_ip6_blackhole"
+
+	vnet_init
+
+	epair=$(vnet_mkepair)
+	epair_out=$(vnet_mkepair)
+
+	ifconfig ${epair}a inet6 2001:db8::2/64 up no_dad
+
+	vnet_mkjail ${jname} ${epair}b ${epair_out}b
+	jexec ${jname} ifconfig lo0 inet6 ::1/128 up no_dad
+	jexec ${jname} ifconfig ${epair}b inet6 2001:db8::1/64 up no_dad
+	jexec ${jname} ifconfig ${epair_out}b inet6 2001:db8:1::1/64 up no_dad
+	jexec ${jname} sysctl net.inet6.ip6.forwarding=1
+
+	route -6 add default 2001:db8::1
+
+	atf_check -s exit:2 -o ignore \
+	    ping6 -c 1 -t 1 2001:db8:1::2
+	atf_check -s exit:0 -o match:"0 packets not forwardable" \
+	    jexec ${jname} netstat -s -p ip6
+
+	# Create blackhole route
+	jexec ${jname} route -6 add 2001:db8:1::2 -blackhole
+
+	# Force slow path
+	jexec ${jname} sysctl net.inet6.ip6.redirect=1
+	atf_check -s exit:2 -o ignore \
+	    ping6 -c 1 -t 1 2001:db8:1::2
+	atf_check -s exit:0 -o match:"1 packet not forwardable" \
+	    jexec ${jname} netstat -s -p ip6
+
+	# Now try the fast path
+	jexec ${jname} sysctl net.inet6.ip6.redirect=0
+	atf_check -s exit:2 -o ignore \
+	    ping6 -c 1 -t 1 2001:db8:1::2
+	atf_check -s exit:0 -o match:"2 packets not forwardable" \
+	    jexec ${jname} netstat -s -p ip6
+}
+
+fwd_ip6_blackhole_cleanup() {
+
+	vnet_cleanup
+}
+
 atf_init_test_cases()
 {
 
@@ -475,6 +528,7 @@ atf_init_test_cases()
 	atf_add_test_case "fwd_ip6_gu_icmp_iface_slow_success"
 	atf_add_test_case "fwd_ip6_gu_icmp_gw_gu_slow_success"
 	atf_add_test_case "fwd_ip6_gu_icmp_gw_ll_slow_success"
+	atf_add_test_case "fwd_ip6_blackhole"
 }
 
 # end