ipfw: fix IPv6 flow label matching

* do not require just only ip6 proto for flow-id opcode in ipfw(8).
  ipv6-icmp, tcp, udp should be fine too.
* fix off-by-one bug leading to out-of-bounds read.
* apply IPV6_FLOWLABEL_MASK before comparison in flow6id_match(),
  so flow-id opcode will match a specified flow label. No need to
  take protocol version and traffic class into account.
* add the test to verify that opcode is working correctly.

Reviewed by:	pouria
Obtained from:	Yandex LLC
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D56869

tests/sys/netpfil/common/pft_ping.py

@@ -63,6 +63,7 @@ def prepare_ipv6(send_params):
     dst_address = send_params.get('dst_address')
     hlim = send_params.get('hlim')
     tc = send_params.get('tc')
+    fl = send_params.get('fl')
     ip6 = sp.IPv6(dst=dst_address)
     if src_address:
         ip6.src = src_address
@@ -70,6 +71,8 @@ def prepare_ipv6(send_params):
         ip6.hlim = hlim
     if tc:
         ip6.tc = tc
+    if fl:
+        ip6.fl = fl
     return ip6
 
 
@@ -224,6 +227,7 @@ def check_ipv6(expect_params, packet):
     flags = expect_params.get('flags')
     hlim = expect_params.get('hlim')
     tc = expect_params.get('tc')
+    fl = expect_params.get('fl')
     ip6 = packet.getlayer(sp.IPv6)
     if not ip6:
         LOGGER.debug('Packet is not IPv6!')
@@ -245,6 +249,9 @@ def check_ipv6(expect_params, packet):
     if tc and ip6.tc != tc:
         LOGGER.debug(f'Wrong TC value {ip6.tc}, expected {tc}')
         return False
+    if fl and ip6.fl != fl:
+        LOGGER.debug(f'Wrong Flow Label value {ip6.fl}, expected {fl}')
+        return False
     return True
 
 
@@ -635,6 +642,8 @@ def parse_args():
         help='ICMP Echo Request payload size')
     parser_send.add_argument('--send-tc', type=int,
         help='IPv6 Traffic Class or IPv4 DiffServ / ToS')
+    parser_send.add_argument('--send-fl', type=int,
+        help='IPv6 Flow label')
     parser_send.add_argument('--send-tcpopt-unaligned', action='store_true',
         help='Include unaligned TCP options')
     parser_send.add_argument('--send-nop', action='store_true',
@@ -652,6 +661,8 @@ def parse_args():
         help='TCP sequence number')
     parser_expect.add_argument('--expect-tc', type=int,
         help='IPv6 Traffic Class or IPv4 DiffServ / ToS')
+    parser_expect.add_argument('--expect-fl', type=int,
+        help='IPv6 Flow Label')
 
     parser.add_argument('-v', '--verbose', action='store_true',
         help=('Enable verbose logging. Apart of potentially useful information '
@@ -673,7 +684,7 @@ def main():
     send_params = {}
     expect_params = {}
     for param_name in (
-        'flags', 'hlim', 'length', 'mss', 'seq', 'tc', 'frag_length',
+        'flags', 'hlim', 'length', 'mss', 'seq', 'tc', 'fl', 'frag_length',
         'sport', 'dport',
     ):
         param_arg = vars(args).get(f'send_{param_name}')

tests/sys/netpfil/ipfw/Makefile

@@ -4,6 +4,7 @@ TESTSDIR=       ${TESTSBASE}/sys/netpfil/ipfw
 
 ATF_TESTS_SH+=	fwd \
 		divert \
+		ipv6-flow-id \
 		log \
 		lookup \
 		table

tests/sys/netpfil/ipfw/ipv6-flow-id.sh

@@ -0,0 +1,78 @@
+#
+# Copyright (c) 2026 Boris Lytochkin
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+common_dir="$(atf_get_srcdir)/../common"
+. ${common_dir}/utils.subr
+
+NC="nc -w 1 -dnN"
+
+setup_network_v6()
+{
+	epair="$1"
+
+	ifconfig ${epair}a inet6 2001:db8:42::1/64 up no_dad -ifdisabled
+
+	vnet_mkjail alcatraz ${epair}b
+
+	ifconfig -j alcatraz ${epair}b inet6 2001:db8:42::2/64 up no_dad -ifdisabled
+
+	jexec alcatraz /usr/sbin/inetd -p /dev/null $(atf_get_srcdir)/lookup_inetd.conf
+
+	# Sanity checks
+	atf_check -s exit:0 -o ignore ping6 -i .1 -c 3 -s 1200 2001:db8:42::2
+	atf_check -o "inline:GOOD 82\n" ${NC} 2001:db8:42::2 82
+}
+
+atf_test_case "ipv6fl" "cleanup"
+
+ipv6fl_head()
+{
+	atf_set descr 'flow-id test'
+	atf_set require.user root
+	atf_set require.progs python3 scapy
+}
+
+ipv6fl_body()
+{
+
+        firewall_init "ipfw"
+
+        epair=$(vnet_mkepair)
+
+        setup_network_v6 ${epair}
+
+	# Check if the firewall is able to match exact IPv6 flow label
+	firewall_config "alcatraz" ipfw ipfw \
+			"ipfw -q add 100 allow ip6 from any to any flow-id 0xbaad" \
+			"ipfw -q add 200 deny ipv6-icmp from any to any icmp6types 128 in"
+
+	# Check Flow Label matches
+	atf_check -s exit:0 ${common_dir}/pft_ping.py \
+		--sendif ${epair}a \
+		--fromaddr 2001:db8:42::1 \
+		--to 2001:db8:42::2 \
+		--send-fl $((0xbaad)) \
+		--replyif ${epair}a
+
+	# Check Flow Label mismatch
+	atf_check -s exit:1 ${common_dir}/pft_ping.py \
+		--sendif ${epair}a \
+		--fromaddr 2001:db8:42::1 \
+		--to 2001:db8:42::2 \
+		--send-fl $((0xf001)) \
+		--replyif ${epair}a
+
+}
+
+ipv6fl_cleanup()
+{
+	firewall_cleanup $1
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case "ipv6fl"
+}