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Fix IPv6 extension header length calculation in dhcp6relay #103

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Xichen96 merged 1 commit into from
Apr 28, 2026
+16 −1
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Fix IPv6 extension header length calculation in dhcp6relay #103

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2 changes: 1 addition & 1 deletion dhcp6relay/src/relay.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -947,7 +947,7 @@ void client_packet_handler(uint8_t *buffer, ssize_t length, struct relay_config
const struct ip6_ext *ext_header;
do {
ext_header = (const struct ip6_ext *)current_position;
current_position += ext_header->ip6e_len;
current_position += (ext_header->ip6e_len + 1) * 8;
if((current_position == prev) ||
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@Xichen96 Xichen96 Apr 28, 2026

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current_position wont be prev under current calculation

(current_position + sizeof(*ext_header) >= buffer_end)) {
return;
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15 changes: 15 additions & 0 deletions dhcp6relay/test/mock_relay.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -721,6 +721,18 @@ TEST(relay, client_packet_handler) {
0x00, 0x00, 0x00, 0x19, 0x00, 0x0c, 0x27, 0xfe, 0x8f, 0x95, 0x00, 0x00, 0x0e, 0x10, 0x00, 0x00,
0x15, 0x18
};
// Packet with Hop-by-Hop extension header (ip6e_len=1 => 16 bytes per RFC 2460: (1+1)*8=16).
// Tests that the extension header pointer arithmetic is correct for nonzero ip6e_len.
// IPv6 next_header=0x00 (HbH), ext: nxt=0x11(UDP), len=0x01 -> advance 16 bytes -> UDP dst=547
uint8_t client_raw_solicit_with_hbh_extension[] = {
0x33, 0x33, 0x00, 0x01, 0x00, 0x02, 0x08, 0x00, 0x27, 0xfe, 0x8f, 0x95, 0x86, 0xdd, 0x60, 0x00,
0x00, 0x00, 0x00, 0x1c, 0x00, 0x01, 0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0a, 0x00,
0x27, 0xff, 0xfe, 0xfe, 0x8f, 0x95, 0xff, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x01, 0x00, 0x02, 0x11, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x22, 0x02, 0x23, 0x00, 0x0c, 0x00, 0x00, 0x01, 0x10,
0x08, 0x74
};

uint8_t non_udp_with_externsion[] = {
0x33, 0x33, 0x00, 0x01, 0x00, 0x02, 0x08, 0x00, 0x27, 0xfe, 0x8f, 0x95, 0x86, 0xdd, 0x60, 0x00,
0x00, 0x00, 0x00, 0x44, 0x2c, 0x01, 0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0a, 0x00,
Expand All @@ -745,6 +757,9 @@ TEST(relay, client_packet_handler) {
ASSERT_NO_THROW(client_packet_handler(client_raw_solicit_with_externsion, sizeof(client_raw_solicit_with_externsion), &config, ifname));

ASSERT_NO_THROW(client_packet_handler(non_udp_with_externsion, sizeof(non_udp_with_externsion), &config, ifname));

// nonzero ip6e_len=1: must advance (1+1)*8=16 bytes per RFC 2460, not 1 byte
ASSERT_NO_THROW(client_packet_handler(client_raw_solicit_with_hbh_extension, sizeof(client_raw_solicit_with_hbh_extension), &config, ifname));
}

MOCK_GLOBAL_FUNC6(recvfrom, ssize_t(int, void *, size_t, int, struct sockaddr *, socklen_t *));
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