mirror of https://github.com/tailscale/tailscale/
net/packet: split off checksum munging into different pkg
The current structure meant that we were embedding netstack in the tailscale CLI and in the GUIs. This removes that by isolating the checksum munging to a different pkg which is only called from `net/tstun`. Fixes #9756 Signed-off-by: Maisem Ali <maisem@tailscale.com>pull/9758/head
Maisem Ali
1 year ago
committed by
Maisem Ali
parent
8b630c91bc
commit
9d96e05267
@ -0,0 +1,21 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package main
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import (
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"testing"
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"tailscale.com/tstest/deptest"
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)
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func TestDeps(t *testing.T) {
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deptest.DepChecker{
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BadDeps: map[string]string{
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"gvisor.dev/gvisor/pkg/buffer": "https://github.com/tailscale/tailscale/issues/9756",
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"gvisor.dev/gvisor/pkg/cpuid": "https://github.com/tailscale/tailscale/issues/9756",
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"gvisor.dev/gvisor/pkg/tcpip": "https://github.com/tailscale/tailscale/issues/9756",
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"gvisor.dev/gvisor/pkg/tcpip/header": "https://github.com/tailscale/tailscale/issues/9756",
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},
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}.Check(t)
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}
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@ -0,0 +1,21 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package ipn
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import (
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"testing"
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"tailscale.com/tstest/deptest"
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)
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func TestDeps(t *testing.T) {
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deptest.DepChecker{
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BadDeps: map[string]string{
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"gvisor.dev/gvisor/pkg/buffer": "https://github.com/tailscale/tailscale/issues/9756",
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"gvisor.dev/gvisor/pkg/cpuid": "https://github.com/tailscale/tailscale/issues/9756",
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"gvisor.dev/gvisor/pkg/tcpip": "https://github.com/tailscale/tailscale/issues/9756",
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"gvisor.dev/gvisor/pkg/tcpip/header": "https://github.com/tailscale/tailscale/issues/9756",
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},
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}.Check(t)
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}
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@ -0,0 +1,197 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package checksum provides functions for updating checksums in parsed packets.
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package checksum
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import (
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"encoding/binary"
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"net/netip"
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"gvisor.dev/gvisor/pkg/tcpip"
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"gvisor.dev/gvisor/pkg/tcpip/header"
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"tailscale.com/net/packet"
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"tailscale.com/types/ipproto"
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)
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// UpdateSrcAddr updates the source address in the packet buffer (e.g. during
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// SNAT). It also updates the checksum. Currently (2023-09-22) only TCP/UDP/ICMP
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// is supported. It panics if provided with an address in a different
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// family to the parsed packet.
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func UpdateSrcAddr(q *packet.Parsed, src netip.Addr) {
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if src.Is6() && q.IPVersion != 6 {
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panic("UpdateSrcAddr: cannot write IPv6 address to v4 packet")
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} else if src.Is4() && q.IPVersion != 4 {
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panic("UpdateSrcAddr: cannot write IPv4 address to v6 packet")
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}
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q.CaptureMeta.DidSNAT = true
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q.CaptureMeta.OriginalSrc = q.Src
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old := q.Src.Addr()
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q.Src = netip.AddrPortFrom(src, q.Src.Port())
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b := q.Buffer()
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if src.Is6() {
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v6 := src.As16()
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copy(b[8:24], v6[:])
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updateV6PacketChecksums(q, old, src)
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} else {
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v4 := src.As4()
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copy(b[12:16], v4[:])
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updateV4PacketChecksums(q, old, src)
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}
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}
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// UpdateDstAddr updates the destination address in the packet buffer (e.g. during
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// DNAT). It also updates the checksum. Currently (2022-12-10) only TCP/UDP/ICMP
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// is supported. It panics if provided with an address in a different
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// family to the parsed packet.
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func UpdateDstAddr(q *packet.Parsed, dst netip.Addr) {
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if dst.Is6() && q.IPVersion != 6 {
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panic("UpdateDstAddr: cannot write IPv6 address to v4 packet")
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} else if dst.Is4() && q.IPVersion != 4 {
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panic("UpdateDstAddr: cannot write IPv4 address to v6 packet")
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}
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q.CaptureMeta.DidDNAT = true
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q.CaptureMeta.OriginalDst = q.Dst
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old := q.Dst.Addr()
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q.Dst = netip.AddrPortFrom(dst, q.Dst.Port())
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b := q.Buffer()
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if dst.Is6() {
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v6 := dst.As16()
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copy(b[24:36], v6[:])
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updateV6PacketChecksums(q, old, dst)
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} else {
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v4 := dst.As4()
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copy(b[16:20], v4[:])
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updateV4PacketChecksums(q, old, dst)
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}
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}
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// updateV4PacketChecksums updates the checksums in the packet buffer.
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// Currently (2023-03-01) only TCP/UDP/ICMP over IPv4 is supported.
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// p is modified in place.
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// If p.IPProto is unknown, only the IP header checksum is updated.
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func updateV4PacketChecksums(p *packet.Parsed, old, new netip.Addr) {
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if len(p.Buffer()) < 12 {
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// Not enough space for an IPv4 header.
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return
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}
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o4, n4 := old.As4(), new.As4()
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// First update the checksum in the IP header.
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updateV4Checksum(p.Buffer()[10:12], o4[:], n4[:])
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// Now update the transport layer checksums, where applicable.
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tr := p.Transport()
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switch p.IPProto {
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case ipproto.UDP, ipproto.DCCP:
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if len(tr) < header.UDPMinimumSize {
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// Not enough space for a UDP header.
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return
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}
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updateV4Checksum(tr[6:8], o4[:], n4[:])
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case ipproto.TCP:
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if len(tr) < header.TCPMinimumSize {
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// Not enough space for a TCP header.
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return
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}
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updateV4Checksum(tr[16:18], o4[:], n4[:])
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case ipproto.GRE:
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if len(tr) < 6 {
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// Not enough space for a GRE header.
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return
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}
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if tr[0] == 1 { // checksum present
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updateV4Checksum(tr[4:6], o4[:], n4[:])
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}
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case ipproto.SCTP, ipproto.ICMPv4:
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// No transport layer update required.
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}
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}
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// updateV6PacketChecksums updates the checksums in the packet buffer.
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// p is modified in place.
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// If p.IPProto is unknown, no checksums are updated.
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func updateV6PacketChecksums(p *packet.Parsed, old, new netip.Addr) {
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if len(p.Buffer()) < 40 {
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// Not enough space for an IPv6 header.
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return
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}
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o6, n6 := tcpip.AddrFrom16Slice(old.AsSlice()), tcpip.AddrFrom16Slice(new.AsSlice())
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// Now update the transport layer checksums, where applicable.
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tr := p.Transport()
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switch p.IPProto {
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case ipproto.ICMPv6:
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if len(tr) < header.ICMPv6MinimumSize {
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return
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}
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header.ICMPv6(tr).UpdateChecksumPseudoHeaderAddress(o6, n6)
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case ipproto.UDP, ipproto.DCCP:
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if len(tr) < header.UDPMinimumSize {
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return
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}
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header.UDP(tr).UpdateChecksumPseudoHeaderAddress(o6, n6, true)
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case ipproto.TCP:
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if len(tr) < header.TCPMinimumSize {
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return
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}
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header.TCP(tr).UpdateChecksumPseudoHeaderAddress(o6, n6, true)
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case ipproto.SCTP:
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// No transport layer update required.
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}
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}
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// updateV4Checksum calculates and updates the checksum in the packet buffer for
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// a change between old and new. The oldSum must point to the 16-bit checksum
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// field in the packet buffer that holds the old checksum value, it will be
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// updated in place.
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//
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// The old and new must be the same length, and must be an even number of bytes.
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func updateV4Checksum(oldSum, old, new []byte) {
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if len(old) != len(new) {
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panic("old and new must be the same length")
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}
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if len(old)%2 != 0 {
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panic("old and new must be of even length")
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}
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/*
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RFC 1624
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Given the following notation:
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HC - old checksum in header
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C - one's complement sum of old header
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HC' - new checksum in header
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C' - one's complement sum of new header
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m - old value of a 16-bit field
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m' - new value of a 16-bit field
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HC' = ~(C + (-m) + m') -- [Eqn. 3]
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HC' = ~(~HC + ~m + m')
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This can be simplified to:
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HC' = ~(C + ~m + m') -- [Eqn. 3]
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HC' = ~C'
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C' = C + ~m + m'
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*/
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c := uint32(^binary.BigEndian.Uint16(oldSum))
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cPrime := c
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for len(new) > 0 {
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mNot := uint32(^binary.BigEndian.Uint16(old[:2]))
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mPrime := uint32(binary.BigEndian.Uint16(new[:2]))
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cPrime += mPrime + mNot
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new, old = new[2:], old[2:]
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}
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// Account for overflows by adding the carry bits back into the sum.
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for (cPrime >> 16) > 0 {
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cPrime = cPrime&0xFFFF + cPrime>>16
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}
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hcPrime := ^uint16(cPrime)
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binary.BigEndian.PutUint16(oldSum, hcPrime)
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}
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@ -0,0 +1,196 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package checksum
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import (
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"encoding/binary"
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"net/netip"
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"testing"
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"gvisor.dev/gvisor/pkg/tcpip"
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"gvisor.dev/gvisor/pkg/tcpip/checksum"
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"gvisor.dev/gvisor/pkg/tcpip/header"
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"tailscale.com/net/packet"
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)
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func fullHeaderChecksumV4(b []byte) uint16 {
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s := uint32(0)
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for i := 0; i < len(b); i += 2 {
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if i == 10 {
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// Skip checksum field.
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continue
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}
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s += uint32(binary.BigEndian.Uint16(b[i : i+2]))
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}
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for s>>16 > 0 {
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s = s&0xFFFF + s>>16
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}
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return ^uint16(s)
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}
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func TestHeaderChecksumsV4(t *testing.T) {
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// This is not a good enough test, because it doesn't
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// check the various packet types or the many edge cases
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// of the checksum algorithm. But it's a start.
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tests := []struct {
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name string
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packet []byte
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}{
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{
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name: "ICMPv4",
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packet: []byte{
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0x45, 0x00, 0x00, 0x54, 0xb7, 0x96, 0x40, 0x00, 0x40, 0x01, 0x7a, 0x06, 0x64, 0x7f, 0x3f, 0x4c, 0x64, 0x40, 0x01, 0x01, 0x08, 0x00, 0x47, 0x1a, 0x00, 0x11, 0x01, 0xac, 0xcc, 0xf5, 0x95, 0x63, 0x00, 0x00, 0x00, 0x00, 0x8d, 0xfc, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
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},
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},
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{
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name: "TLS",
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packet: []byte{
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0x45, 0x00, 0x00, 0x3c, 0x54, 0x29, 0x40, 0x00, 0x40, 0x06, 0xb1, 0xac, 0x64, 0x42, 0xd4, 0x33, 0x64, 0x61, 0x98, 0x0f, 0xb1, 0x94, 0x01, 0xbb, 0x0a, 0x51, 0xce, 0x7c, 0x00, 0x00, 0x00, 0x00, 0xa0, 0x02, 0xfb, 0xe0, 0x38, 0xf6, 0x00, 0x00, 0x02, 0x04, 0x04, 0xd8, 0x04, 0x02, 0x08, 0x0a, 0x86, 0x2b, 0xcc, 0xd5, 0x00, 0x00, 0x00, 0x00, 0x01, 0x03, 0x03, 0x07,
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},
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},
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{
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name: "DNS",
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packet: []byte{
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0x45, 0x00, 0x00, 0x74, 0xe2, 0x85, 0x00, 0x00, 0x40, 0x11, 0x96, 0xb5, 0x64, 0x64, 0x64, 0x64, 0x64, 0x42, 0xd4, 0x33, 0x00, 0x35, 0xec, 0x55, 0x00, 0x60, 0xd9, 0x19, 0xed, 0xfd, 0x81, 0x80, 0x00, 0x01, 0x00, 0x02, 0x00, 0x00, 0x00, 0x01, 0x08, 0x63, 0x6c, 0x69, 0x65, 0x6e, 0x74, 0x73, 0x34, 0x06, 0x67, 0x6f, 0x6f, 0x67, 0x6c, 0x65, 0x03, 0x63, 0x6f, 0x6d, 0x00, 0x00, 0x01, 0x00, 0x01, 0xc0, 0x0c, 0x00, 0x05, 0x00, 0x01, 0x00, 0x00, 0x01, 0x1e, 0x00, 0x0c, 0x07, 0x63, 0x6c, 0x69, 0x65, 0x6e, 0x74, 0x73, 0x01, 0x6c, 0xc0, 0x15, 0xc0, 0x31, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x01, 0x1e, 0x00, 0x04, 0x8e, 0xfa, 0xbd, 0xce, 0x00, 0x00, 0x29, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
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},
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},
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{
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name: "DCCP",
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packet: []byte{
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0x45, 0x00, 0x00, 0x28, 0x15, 0x06, 0x40, 0x00, 0x40, 0x21, 0x5f, 0x2f, 0xc0, 0xa8, 0x01, 0x1f, 0xc9, 0x0b, 0x3b, 0xad, 0x80, 0x04, 0x13, 0x89, 0x05, 0x00, 0x08, 0xdb, 0x01, 0x00, 0x00, 0x04, 0x29, 0x01, 0x6d, 0xdc, 0x00, 0x00, 0x00, 0x00,
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},
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},
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{
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name: "SCTP",
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packet: []byte{
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0x45, 0x00, 0x00, 0x30, 0x09, 0xd9, 0x40, 0x00, 0xff, 0x84, 0x50, 0xe2, 0x0a, 0x1c, 0x06, 0x2c, 0x0a, 0x1c, 0x06, 0x2b, 0x0b, 0x80, 0x40, 0x00, 0x21, 0x44, 0x15, 0x23, 0x2b, 0xf2, 0x02, 0x4e, 0x03, 0x00, 0x00, 0x10, 0x28, 0x02, 0x43, 0x45, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00,
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},
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},
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// TODO(maisem): add test for GRE.
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}
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var p packet.Parsed
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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p.Decode(tt.packet)
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t.Log(p.String())
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UpdateSrcAddr(&p, netip.MustParseAddr("100.64.0.1"))
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got := binary.BigEndian.Uint16(tt.packet[10:12])
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want := fullHeaderChecksumV4(tt.packet[:20])
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if got != want {
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t.Fatalf("got %x want %x", got, want)
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}
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UpdateDstAddr(&p, netip.MustParseAddr("100.64.0.2"))
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got = binary.BigEndian.Uint16(tt.packet[10:12])
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want = fullHeaderChecksumV4(tt.packet[:20])
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if got != want {
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t.Fatalf("got %x want %x", got, want)
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}
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})
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}
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}
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func TestNatChecksumsV6UDP(t *testing.T) {
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a1, a2 := netip.MustParseAddr("a::1"), netip.MustParseAddr("b::1")
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// Make a fake UDP packet with 32 bytes of zeros as the datagram payload.
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b := header.IPv6(make([]byte, header.IPv6MinimumSize+header.UDPMinimumSize+32))
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b.Encode(&header.IPv6Fields{
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PayloadLength: header.UDPMinimumSize + 32,
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TransportProtocol: header.UDPProtocolNumber,
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HopLimit: 16,
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SrcAddr: tcpip.AddrFrom16Slice(a1.AsSlice()),
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DstAddr: tcpip.AddrFrom16Slice(a2.AsSlice()),
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})
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udp := header.UDP(b[header.IPv6MinimumSize:])
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udp.Encode(&header.UDPFields{
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SrcPort: 42,
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DstPort: 43,
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Length: header.UDPMinimumSize + 32,
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})
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xsum := header.PseudoHeaderChecksum(
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header.UDPProtocolNumber,
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tcpip.AddrFrom16Slice(a1.AsSlice()),
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tcpip.AddrFrom16Slice(a2.AsSlice()),
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uint16(header.UDPMinimumSize+32),
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)
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xsum = checksum.Checksum(b.Payload()[header.UDPMinimumSize:], xsum)
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udp.SetChecksum(^udp.CalculateChecksum(xsum))
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if !udp.IsChecksumValid(tcpip.AddrFrom16Slice(a1.AsSlice()), tcpip.AddrFrom16Slice(a2.AsSlice()), checksum.Checksum(b.Payload()[header.UDPMinimumSize:], 0)) {
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t.Fatal("test broken; initial packet has incorrect checksum")
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}
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// Parse the packet.
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var p packet.Parsed
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p.Decode(b)
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t.Log(p.String())
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|
||||
// Update the source address of the packet to be the same as the dest.
|
||||
UpdateSrcAddr(&p, a2)
|
||||
if !udp.IsChecksumValid(tcpip.AddrFrom16Slice(a2.AsSlice()), tcpip.AddrFrom16Slice(a2.AsSlice()), checksum.Checksum(b.Payload()[header.UDPMinimumSize:], 0)) {
|
||||
t.Fatal("incorrect checksum after updating source address")
|
||||
}
|
||||
|
||||
// Update the dest address of the packet to be the original source address.
|
||||
UpdateDstAddr(&p, a1)
|
||||
if !udp.IsChecksumValid(tcpip.AddrFrom16Slice(a2.AsSlice()), tcpip.AddrFrom16Slice(a1.AsSlice()), checksum.Checksum(b.Payload()[header.UDPMinimumSize:], 0)) {
|
||||
t.Fatal("incorrect checksum after updating destination address")
|
||||
}
|
||||
}
|
||||
|
||||
func TestNatChecksumsV6TCP(t *testing.T) {
|
||||
a1, a2 := netip.MustParseAddr("a::1"), netip.MustParseAddr("b::1")
|
||||
|
||||
// Make a fake TCP packet with no payload.
|
||||
b := header.IPv6(make([]byte, header.IPv6MinimumSize+header.TCPMinimumSize))
|
||||
b.Encode(&header.IPv6Fields{
|
||||
PayloadLength: header.TCPMinimumSize,
|
||||
TransportProtocol: header.TCPProtocolNumber,
|
||||
HopLimit: 16,
|
||||
SrcAddr: tcpip.AddrFrom16Slice(a1.AsSlice()),
|
||||
DstAddr: tcpip.AddrFrom16Slice(a2.AsSlice()),
|
||||
})
|
||||
tcp := header.TCP(b[header.IPv6MinimumSize:])
|
||||
tcp.Encode(&header.TCPFields{
|
||||
SrcPort: 42,
|
||||
DstPort: 43,
|
||||
SeqNum: 1,
|
||||
AckNum: 2,
|
||||
DataOffset: header.TCPMinimumSize,
|
||||
Flags: 3,
|
||||
WindowSize: 4,
|
||||
Checksum: 0,
|
||||
UrgentPointer: 5,
|
||||
})
|
||||
xsum := header.PseudoHeaderChecksum(
|
||||
header.TCPProtocolNumber,
|
||||
tcpip.AddrFrom16Slice(a1.AsSlice()),
|
||||
tcpip.AddrFrom16Slice(a2.AsSlice()),
|
||||
uint16(header.TCPMinimumSize),
|
||||
)
|
||||
tcp.SetChecksum(^tcp.CalculateChecksum(xsum))
|
||||
|
||||
if !tcp.IsChecksumValid(tcpip.AddrFrom16Slice(a1.AsSlice()), tcpip.AddrFrom16Slice(a2.AsSlice()), 0, 0) {
|
||||
t.Fatal("test broken; initial packet has incorrect checksum")
|
||||
}
|
||||
|
||||
// Parse the packet.
|
||||
var p packet.Parsed
|
||||
p.Decode(b)
|
||||
t.Log(p.String())
|
||||
|
||||
// Update the source address of the packet to be the same as the dest.
|
||||
UpdateSrcAddr(&p, a2)
|
||||
if !tcp.IsChecksumValid(tcpip.AddrFrom16Slice(a2.AsSlice()), tcpip.AddrFrom16Slice(a2.AsSlice()), 0, 0) {
|
||||
t.Fatal("incorrect checksum after updating source address")
|
||||
}
|
||||
|
||||
// Update the dest address of the packet to be the original source address.
|
||||
UpdateDstAddr(&p, a1)
|
||||
if !tcp.IsChecksumValid(tcpip.AddrFrom16Slice(a2.AsSlice()), tcpip.AddrFrom16Slice(a1.AsSlice()), 0, 0) {
|
||||
t.Fatal("incorrect checksum after updating destination address")
|
||||
}
|
||||
}
|
||||
Loading…
Reference in New Issue