pf: fix 'natpass'

If an rdr (or nat) rule specifies 'pass' we don't run the filter rules, we just
pass the traffic. Or at least, we did until that got unintentionally broken.
Restore that behaviour and add a test case.

While here also fix nat:dummynet_mask, which relied on the broken behaviour.

MFC after:	3 days
Sponsored by:	Rubicon Communications, LLC ("Netgate")
Differential Revision:	https://reviews.freebsd.org/D52838

tests/sys/netpfil/pf/nat.sh

@@ -838,7 +838,7 @@ dummynet_mask_body()
 	jexec gw dnctl pipe 1 config delay 100 mask src-ip 0xffffff00
 	jexec gw pfctl -e
 	pft_set_rules gw \
-	    "nat pass on ${epair_srv}b inet from 192.0.2.0/24 to any -> (${epair_srv}b)" \
+	    "nat on ${epair_srv}b inet from 192.0.2.0/24 to any -> (${epair_srv}b)" \
 	    "pass out dnpipe 1"
 
 	atf_check -s exit:0 -o ignore \

tests/sys/netpfil/pf/rdr.sh

@@ -281,8 +281,66 @@ srcport_pass_cleanup()
 	pft_cleanup
 }
 
+atf_test_case "natpass" "cleanup"
+natpass_head()
+{
+	atf_set descr 'Test rdr pass'
+	atf_set require.user root
+}
+
+natpass_body()
+{
+	pft_init
+
+	epair=$(vnet_mkepair)
+	epair_link=$(vnet_mkepair)
+
+	ifconfig ${epair}a 192.0.2.2/24 up
+
+	vnet_mkjail alcatraz ${epair}b ${epair_link}a
+	jexec alcatraz ifconfig lo0 inet 127.0.0.1/8 up
+	jexec alcatraz ifconfig ${epair}b inet 192.0.2.1/24 up
+	jexec alcatraz ifconfig ${epair_link}a 198.51.100.1/24 up
+	jexec alcatraz sysctl net.inet.ip.forwarding=1
+
+	vnet_mkjail srv ${epair_link}b
+	jexec srv ifconfig ${epair_link}b inet 198.51.100.2/24 up
+	jexec srv route add default 198.51.100.1
+
+	# Sanity check
+	atf_check -s exit:0 -o ignore \
+	    ping -c 1 192.0.2.1
+	atf_check -s exit:0 -o ignore \
+	    jexec alcatraz ping -c 1 198.51.100.2
+
+	jexec alcatraz pfctl -e
+	pft_set_rules alcatraz \
+	    "rdr pass on ${epair}b proto udp from any to 192.0.2.1 port 80 -> 198.51.100.2" \
+	    "nat on ${epair}b inet from 198.51.100.0/24 to any -> 192.0.2.1" \
+	    "block in proto udp from any to any port 80" \
+	    "pass in proto icmp"
+
+	echo "foo" | jexec srv nc -u -l 80 &
+	sleep 1 # Give the above a moment to start
+
+	out=$(echo 1 | nc -u -w 1 192.0.2.1 80)
+	echo "out ${out}"
+	if [ "${out}" != "foo" ];
+	then
+		jexec alcatraz pfctl -sn -vv
+		jexec alcatraz pfctl -ss -vv
+		atf_fail "rdr failed"
+	fi
+}
+
+natpass_cleanup()
+{
+	pft_cleanup
+}
+
 atf_init_test_cases()
 {
+	atf_add_test_case "natpass"
 	atf_add_test_case "tcp_v6_compat"
 	atf_add_test_case "tcp_v6_pass"
 	atf_add_test_case "srcport_compat"