mirror of
https://github.com/slackhq/nebula.git
synced 2026-08-15 22:57:03 +02:00
JackDoan
603 lines
22 KiB
Go
603 lines
22 KiB
Go
//go:build linux && !android
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// +build linux,!android
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package virtio
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import (
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"bytes"
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"encoding/binary"
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"testing"
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"golang.org/x/sys/unix"
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"github.com/slackhq/nebula/overlay/checksum"
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)
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// verifyChecksum confirms that the one's-complement sum across b, seeded with
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// a folded pseudo-header sum, equals all-ones (a valid on-wire checksum).
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// A corrupted header stamped into a segment makes this fail even when the
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// checksum field itself was computed from the (pristine) base sums, because
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// the bytes the receiver would sum no longer match what was checksummed.
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func verifyChecksum(b []byte, pseudo uint16) bool {
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return checksum.Checksum(b, pseudo) == 0xffff
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}
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// pseudoHeaderIPv4 folds the TCP/UDP pseudo-header sum from a segment's own
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// address and length fields, used to independently verify its L4 checksum.
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func pseudoHeaderIPv4(src, dst []byte, proto byte, l4Len int) uint16 {
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s := uint32(checksum.Checksum(src, 0)) + uint32(checksum.Checksum(dst, 0))
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s += uint32(proto) + uint32(l4Len)
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s = (s & 0xffff) + (s >> 16)
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s = (s & 0xffff) + (s >> 16)
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return uint16(s)
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}
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// buildTCPv4Super constructs a synthetic IPv4/TCP TSO superpacket with a
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// payload of payLen bytes and returns it alongside the header fields the
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// segmenter needs. The header is a fixed 40 bytes (20 IPv4 + 20 TCP).
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func buildTCPv4Super(payLen int) (pkt []byte, hdrLen, csumStart uint16) {
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const ipLen = 20
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const tcpLen = 20
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pkt = make([]byte, ipLen+tcpLen+payLen)
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// IPv4 header.
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pkt[0] = 0x45 // version 4, IHL 5
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binary.BigEndian.PutUint16(pkt[2:4], uint16(ipLen+tcpLen+payLen))
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binary.BigEndian.PutUint16(pkt[4:6], 0x4242) // ID
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pkt[8] = 64 // TTL
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pkt[9] = unix.IPPROTO_TCP
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copy(pkt[12:16], []byte{10, 0, 0, 1}) // src
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copy(pkt[16:20], []byte{10, 0, 0, 2}) // dst
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// TCP header.
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binary.BigEndian.PutUint16(pkt[20:22], 12345) // sport
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binary.BigEndian.PutUint16(pkt[22:24], 80) // dport
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binary.BigEndian.PutUint32(pkt[24:28], 10000) // seq
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binary.BigEndian.PutUint32(pkt[28:32], 20000) // ack
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pkt[32] = 0x50 // data offset 5 words
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pkt[33] = 0x18 // ACK | PSH
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binary.BigEndian.PutUint16(pkt[34:36], 65535) // window
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for i := 0; i < payLen; i++ {
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pkt[ipLen+tcpLen+i] = byte(i & 0xff)
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}
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return pkt, ipLen + tcpLen, ipLen
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}
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// buildUDPv4Super constructs a synthetic IPv4/UDP USO superpacket with a
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// payload of payLen bytes. Header is a fixed 28 bytes (20 IPv4 + 8 UDP).
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func buildUDPv4Super(payLen int) (pkt []byte, hdrLen, csumStart uint16) {
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const ipLen = 20
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const udpLen = 8
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pkt = make([]byte, ipLen+udpLen+payLen)
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pkt[0] = 0x45
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binary.BigEndian.PutUint16(pkt[2:4], uint16(ipLen+udpLen+payLen))
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binary.BigEndian.PutUint16(pkt[4:6], 0x4242)
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pkt[8] = 64
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pkt[9] = unix.IPPROTO_UDP
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copy(pkt[12:16], []byte{10, 0, 0, 1})
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copy(pkt[16:20], []byte{10, 0, 0, 2})
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binary.BigEndian.PutUint16(pkt[20:22], 12345) // sport
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binary.BigEndian.PutUint16(pkt[22:24], 53) // dport
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for i := 0; i < payLen; i++ {
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pkt[ipLen+udpLen+i] = byte(i & 0xff)
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}
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return pkt, ipLen + udpLen, ipLen
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}
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// collectTCP segments a fresh copy of pkt and returns each segment as an
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// independent slice so assertions can run after segmentation completes.
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func collectTCP(t *testing.T, pkt []byte, hdrLen, csumStart, gsoSize uint16) [][]byte {
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t.Helper()
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work := append([]byte(nil), pkt...)
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var out [][]byte
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err := SegmentTCP(work, hdrLen, csumStart, gsoSize, func(seg []byte) error {
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out = append(out, append([]byte(nil), seg...))
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return nil
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})
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if err != nil {
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t.Fatalf("SegmentTCP: %v", err)
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}
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return out
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}
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func collectUDP(t *testing.T, pkt []byte, hdrLen, csumStart, gsoSize uint16) [][]byte {
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t.Helper()
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work := append([]byte(nil), pkt...)
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var out [][]byte
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err := SegmentUDP(work, hdrLen, csumStart, gsoSize, func(seg []byte) error {
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out = append(out, append([]byte(nil), seg...))
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return nil
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})
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if err != nil {
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t.Fatalf("SegmentUDP: %v", err)
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}
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return out
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}
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// TestSegmentTCPHeaderNotCorrupted is the regression test for the in-place
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// header-slide bug: when gsoSize < headerLen the old code stamped each
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// segment's header from pkt[:headerLen], which had already been overwritten
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// by the previous segment's overlapping stamp, so segments 2..n carried a
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// corrupted header (garbage src/dst/ports/seq). Every segment must instead
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// carry the ORIGINAL constant header fields with correct per-segment seq.
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func TestSegmentTCPHeaderNotCorrupted(t *testing.T) {
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const origSeq = 10000
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cases := []struct {
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name string
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payLen int
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gsoSize uint16
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}{
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// gsoSize (8) < headerLen (40): the bug's trigger. Even split.
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{"small-gso-even", 40, 8},
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// gsoSize (8) < headerLen (40) with a short final segment.
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{"small-gso-odd-tail", 44, 8},
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// gsoSize (100) >= headerLen (40): the normal path, must still work.
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{"normal-gso", 250, 100},
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}
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for _, tc := range cases {
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t.Run(tc.name, func(t *testing.T) {
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pkt, hdrLen, csumStart := buildTCPv4Super(tc.payLen)
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gso := int(tc.gsoSize)
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wantSeg := (tc.payLen + gso - 1) / gso
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segs := collectTCP(t, pkt, hdrLen, csumStart, tc.gsoSize)
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if len(segs) != wantSeg {
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t.Fatalf("got %d segments, want %d", len(segs), wantSeg)
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}
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off := 0
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for i, seg := range segs {
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// Constant header fields must be identical to the original in
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// EVERY segment. These are exactly the bytes the old code
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// corrupted in segments 2..n.
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if got := seg[0]; got != 0x45 {
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t.Errorf("seg %d: version/IHL byte=%#x want 0x45", i, got)
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}
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if seg[9] != unix.IPPROTO_TCP {
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t.Errorf("seg %d: proto=%d want %d", i, seg[9], unix.IPPROTO_TCP)
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}
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if !bytes.Equal(seg[12:16], []byte{10, 0, 0, 1}) {
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t.Errorf("seg %d: src=%v want [10 0 0 1]", i, seg[12:16])
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}
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if !bytes.Equal(seg[16:20], []byte{10, 0, 0, 2}) {
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t.Errorf("seg %d: dst=%v want [10 0 0 2]", i, seg[16:20])
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}
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if sport := binary.BigEndian.Uint16(seg[20:22]); sport != 12345 {
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t.Errorf("seg %d: sport=%d want 12345", i, sport)
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}
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if dport := binary.BigEndian.Uint16(seg[22:24]); dport != 80 {
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t.Errorf("seg %d: dport=%d want 80", i, dport)
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}
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if ack := binary.BigEndian.Uint32(seg[28:32]); ack != 20000 {
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t.Errorf("seg %d: ack=%d want 20000", i, ack)
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}
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if seg[32] != 0x50 {
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t.Errorf("seg %d: data-offset byte=%#x want 0x50", i, seg[32])
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}
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// Per-segment seq must advance by the payload offset.
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segStart := i * gso
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if seq := binary.BigEndian.Uint32(seg[24:28]); seq != uint32(origSeq+segStart) {
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t.Errorf("seg %d: seq=%d want %d", i, seq, origSeq+segStart)
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}
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// Payload bytes must be the original contiguous slice.
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segPayLen := len(seg) - int(hdrLen)
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wantPay := make([]byte, segPayLen)
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for k := 0; k < segPayLen; k++ {
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wantPay[k] = byte((off + k) & 0xff)
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}
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if !bytes.Equal(seg[hdrLen:], wantPay) {
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t.Errorf("seg %d: payload mismatch", i)
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}
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off += segPayLen
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// End-to-end: the stamped header must checksum-verify. A
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// corrupted header fails here because the written checksum was
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// derived from the pristine header.
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if !verifyChecksum(seg[:20], 0) {
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t.Errorf("seg %d: bad IPv4 header checksum", i)
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}
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psum := pseudoHeaderIPv4(seg[12:16], seg[16:20], unix.IPPROTO_TCP, len(seg)-20)
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if !verifyChecksum(seg[20:], psum) {
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t.Errorf("seg %d: bad TCP checksum", i)
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}
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}
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})
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}
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}
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// TestCorrectHdrLenChecksumBound guards the checksum-field bounds check in
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// CorrectHdrLen. The checksum field sits at CsumStart+CsumOffset, so the check
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// must be computed from CsumStart+CsumOffset — NOT CsumStart+CsumStart, a
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// regression that doubled CsumStart and thus over-tightened the bound (since
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// CsumOffset, 6 for UDP / 16 for TCP, is always < CsumStart >= 20). That bogus
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// bound spuriously rejected valid small USO superpackets in decodeRead.
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func TestCorrectHdrLenChecksumBound(t *testing.T) {
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// A valid IPv4 USO superpacket: 20B IPv4 + 8B UDP + two 6-byte segments
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// (payload 12) = 40 bytes total. CsumStart=20, CsumOffset=6, so the UDP
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// checksum field lives at bytes 26..27, comfortably inside the 40-byte
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// packet. The OLD formula computed cSumAt = CsumStart+CsumStart = 40 and
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// rejected on cSumAt+1 (41) >= len(pkt) (40); the fix (CsumStart+CsumOffset
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// = 26) accepts. This case FAILS against the CsumStart+CsumStart regression.
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t.Run("valid-small-uso-accepted", func(t *testing.T) {
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pkt, _, csumStart := buildUDPv4Super(12) // total len 40
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hdr := NewHeader(
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unix.VIRTIO_NET_HDR_F_NEEDS_CSUM, /*flags*/
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unix.VIRTIO_NET_HDR_GSO_UDP_L4, /*gsoType*/
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0, /*hdrLen*/
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6, /*gsoSize: two 6-byte segments*/
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csumStart, /*csumStart*/
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6, /*csumOffset*/
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)
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if err := CorrectHdrLen(pkt, &hdr); err != nil {
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t.Fatalf("CorrectHdrLen rejected a valid 40-byte USO superpacket: %v", err)
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}
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if hdr.HdrLen != csumStart+udpHeaderLen {
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t.Errorf("HdrLen = %d, want %d", hdr.HdrLen, csumStart+udpHeaderLen)
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}
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})
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// A genuinely-too-short packet: CsumStart=20, CsumOffset=6 means the
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// checksum field would end at byte 27, but the packet is only 25 bytes
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// (CsumStart+CsumOffset+2 = 28 > 25). CorrectHdrLen must still reject it.
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t.Run("too-short-rejected", func(t *testing.T) {
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pkt := make([]byte, 25)
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pkt[0] = 0x45 // IPv4, IHL 5
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hdr := NewHeader(
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unix.VIRTIO_NET_HDR_F_NEEDS_CSUM, /*flags*/
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unix.VIRTIO_NET_HDR_GSO_UDP_L4, /*gsoType*/
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0, /*hdrLen*/
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6, /*gsoSize*/
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20, /*csumStart*/
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6, /*csumOffset*/
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)
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if err := CorrectHdrLen(pkt, &hdr); err == nil {
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t.Fatalf("CorrectHdrLen accepted a too-short (25-byte) packet")
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}
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})
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}
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// TestSegmentUDPHeaderNotCorrupted is the USO counterpart: SegmentUDP performs
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// the same header stamp and must be correct when gsoSize < headerLen.
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func TestSegmentUDPHeaderNotCorrupted(t *testing.T) {
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cases := []struct {
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name string
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payLen int
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gsoSize uint16
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}{
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{"small-gso-even", 40, 8},
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{"small-gso-odd-tail", 44, 8},
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{"normal-gso", 250, 100},
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}
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for _, tc := range cases {
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t.Run(tc.name, func(t *testing.T) {
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pkt, hdrLen, csumStart := buildUDPv4Super(tc.payLen)
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gso := int(tc.gsoSize)
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wantSeg := (tc.payLen + gso - 1) / gso
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segs := collectUDP(t, pkt, hdrLen, csumStart, tc.gsoSize)
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if len(segs) != wantSeg {
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t.Fatalf("got %d segments, want %d", len(segs), wantSeg)
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}
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off := 0
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for i, seg := range segs {
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if got := seg[0]; got != 0x45 {
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t.Errorf("seg %d: version/IHL byte=%#x want 0x45", i, got)
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}
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if seg[9] != unix.IPPROTO_UDP {
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t.Errorf("seg %d: proto=%d want %d", i, seg[9], unix.IPPROTO_UDP)
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}
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if !bytes.Equal(seg[12:16], []byte{10, 0, 0, 1}) {
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t.Errorf("seg %d: src=%v want [10 0 0 1]", i, seg[12:16])
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}
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if !bytes.Equal(seg[16:20], []byte{10, 0, 0, 2}) {
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t.Errorf("seg %d: dst=%v want [10 0 0 2]", i, seg[16:20])
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}
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if sport := binary.BigEndian.Uint16(seg[20:22]); sport != 12345 {
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t.Errorf("seg %d: sport=%d want 12345", i, sport)
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}
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if dport := binary.BigEndian.Uint16(seg[22:24]); dport != 53 {
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t.Errorf("seg %d: dport=%d want 53", i, dport)
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}
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// Software UDP GSO bumps the IPv4 ID per segment just like TSO
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// (inet_gso_segment's fixed-ID case is TCP-only).
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if id := binary.BigEndian.Uint16(seg[4:6]); id != 0x4242+uint16(i) {
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t.Errorf("seg %d: ip id=%#x want %#x", i, id, 0x4242+uint16(i))
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}
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segPayLen := len(seg) - int(hdrLen)
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if udpLen := binary.BigEndian.Uint16(seg[24:26]); udpLen != uint16(8+segPayLen) {
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t.Errorf("seg %d: udp len=%d want %d", i, udpLen, 8+segPayLen)
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}
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wantPay := make([]byte, segPayLen)
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for k := 0; k < segPayLen; k++ {
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wantPay[k] = byte((off + k) & 0xff)
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}
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if !bytes.Equal(seg[hdrLen:], wantPay) {
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t.Errorf("seg %d: payload mismatch", i)
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}
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off += segPayLen
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if !verifyChecksum(seg[:20], 0) {
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t.Errorf("seg %d: bad IPv4 header checksum", i)
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}
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psum := pseudoHeaderIPv4(seg[12:16], seg[16:20], unix.IPPROTO_UDP, len(seg)-20)
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if !verifyChecksum(seg[20:], psum) {
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t.Errorf("seg %d: bad UDP checksum", i)
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}
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}
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})
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}
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}
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// buildUDPv4Single constructs a single IPv4/UDP datagram with the checksum field pre-loaded with the folded
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// pseudo-header sum, which is how a NEEDS_CSUM (CHECKSUM_PARTIAL) packet arrives from the tun.
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func buildUDPv4Single(payload []byte) (pkt []byte, hdr Hdr) {
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const ipLen, udpLen = 20, 8
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pkt = make([]byte, ipLen+udpLen+len(payload))
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pkt[0] = 0x45
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binary.BigEndian.PutUint16(pkt[2:4], uint16(len(pkt)))
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pkt[8] = 64
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pkt[9] = unix.IPPROTO_UDP
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copy(pkt[12:16], []byte{10, 0, 0, 1})
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copy(pkt[16:20], []byte{10, 0, 0, 2})
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binary.BigEndian.PutUint16(pkt[ipLen:ipLen+2], 12345)
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binary.BigEndian.PutUint16(pkt[ipLen+2:ipLen+4], 53)
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binary.BigEndian.PutUint16(pkt[ipLen+4:ipLen+6], uint16(udpLen+len(payload)))
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copy(pkt[ipLen+udpLen:], payload)
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pseudo := pseudoHeaderIPv4(pkt[12:16], pkt[16:20], unix.IPPROTO_UDP, udpLen+len(payload))
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binary.BigEndian.PutUint16(pkt[ipLen+udpChecksumOff:ipLen+udpChecksumOff+2], pseudo)
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return pkt, NewHeader(unix.VIRTIO_NET_HDR_F_NEEDS_CSUM, unix.VIRTIO_NET_HDR_GSO_NONE, 0, 0, ipLen, udpChecksumOff)
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}
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// TestFinishChecksumUDPZeroStoresAllOnes pins RFC 768: a UDP checksum that computes to zero goes on the wire as
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// 0xffff, because all-zero is the reserved "no checksum" encoding that IPv6 rejects outright.
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func TestFinishChecksumUDPZeroStoresAllOnes(t *testing.T) {
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var payload []byte
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for i := 0; i < 0x10000; i++ {
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p := []byte{byte(i >> 8), byte(i)}
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pkt, hdr := buildUDPv4Single(p)
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cs, co := int(hdr.CsumStart), int(hdr.CsumOffset)
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partial := binary.BigEndian.Uint16(pkt[cs+co : cs+co+2])
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pkt[cs+co], pkt[cs+co+1] = 0, 0
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if ^checksum.Checksum(pkt[cs:], partial) == 0 {
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payload = p
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break
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}
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}
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if payload == nil {
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t.Fatal("no 2-byte payload produced a zero checksum")
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}
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pkt, hdr := buildUDPv4Single(payload)
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if err := FinishChecksum(pkt, hdr); err != nil {
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t.Fatalf("FinishChecksum: %v", err)
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}
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off := int(hdr.CsumStart) + int(hdr.CsumOffset)
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if got := binary.BigEndian.Uint16(pkt[off : off+2]); got != 0xffff {
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t.Fatalf("stored %#04x, want 0xffff for a UDP checksum that folds to zero", got)
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}
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}
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// TestFinishChecksumTCPZeroPreserved is the other half of the protocol split: zero is a legal TCP checksum and must
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// be stored as-is, so the UDP rewrite must not fire on a TCP csum_offset.
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func TestFinishChecksumTCPZeroPreserved(t *testing.T) {
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const cs, co = 20, tcpChecksumOff
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// Seed the partial so the completed checksum lands on zero, the case the UDP path rewrites.
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seg := make([]byte, cs+co+2)
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for i := range seg[cs:] {
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seg[cs+i] = byte(i * 7)
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}
|
|
var partial uint16
|
|
for i := 0; i <= 0xffff; i++ {
|
|
binary.BigEndian.PutUint16(seg[cs+co:cs+co+2], uint16(i))
|
|
probe := append([]byte(nil), seg...)
|
|
probe[cs+co], probe[cs+co+1] = 0, 0
|
|
if ^checksum.Checksum(probe[cs:], uint16(i)) == 0 {
|
|
partial = uint16(i)
|
|
break
|
|
}
|
|
}
|
|
binary.BigEndian.PutUint16(seg[cs+co:cs+co+2], partial)
|
|
|
|
hdr := NewHeader(unix.VIRTIO_NET_HDR_F_NEEDS_CSUM, unix.VIRTIO_NET_HDR_GSO_NONE, 0, 0, cs, co)
|
|
if err := FinishChecksum(seg, hdr); err != nil {
|
|
t.Fatalf("FinishChecksum: %v", err)
|
|
}
|
|
if got := binary.BigEndian.Uint16(seg[cs+co : cs+co+2]); got != 0 {
|
|
t.Fatalf("stored %#04x, want 0x0000 (zero is a legal TCP checksum)", got)
|
|
}
|
|
}
|
|
|
|
// TestFinishChecksumUDPValidates confirms the ordinary path still produces a checksum a receiver accepts.
|
|
func TestFinishChecksumUDPValidates(t *testing.T) {
|
|
payload := []byte("the definitive tun offloads branch")
|
|
pkt, hdr := buildUDPv4Single(payload)
|
|
if err := FinishChecksum(pkt, hdr); err != nil {
|
|
t.Fatalf("FinishChecksum: %v", err)
|
|
}
|
|
pseudo := pseudoHeaderIPv4(pkt[12:16], pkt[16:20], unix.IPPROTO_UDP, 8+len(payload))
|
|
if !verifyChecksum(pkt[hdr.CsumStart:], pseudo) {
|
|
t.Fatal("completed UDP checksum does not validate")
|
|
}
|
|
}
|
|
|
|
// TestCheckValidMasksGSOECN: GSO_ECN is a qualifier bit the kernel ORs
|
|
// into gso_type for TSO superpackets with CWR set. CheckValid must
|
|
// validate an ECN-qualified type as its base type — previously TCPV4|ECN
|
|
// fell into the default case and skipped the IP-version agreement check.
|
|
// The qualifier is TCP-only, so it must be rejected on UDP_L4.
|
|
func TestCheckValidMasksGSOECN(t *testing.T) {
|
|
v4pkt, _, _ := buildTCPv4Super(100)
|
|
v6pkt := make([]byte, len(v4pkt))
|
|
copy(v6pkt, v4pkt)
|
|
v6pkt[0] = 0x60 // claim IPv6
|
|
|
|
cases := []struct {
|
|
name string
|
|
pkt []byte
|
|
gsoType uint8
|
|
wantErr bool
|
|
}{
|
|
{"tcpv4-ecn-v4", v4pkt, unix.VIRTIO_NET_HDR_GSO_TCPV4 | unix.VIRTIO_NET_HDR_GSO_ECN, false},
|
|
{"tcpv4-ecn-v6-mismatch", v6pkt, unix.VIRTIO_NET_HDR_GSO_TCPV4 | unix.VIRTIO_NET_HDR_GSO_ECN, true},
|
|
{"tcpv6-ecn-v4-mismatch", v4pkt, unix.VIRTIO_NET_HDR_GSO_TCPV6 | unix.VIRTIO_NET_HDR_GSO_ECN, true},
|
|
{"udp-l4-ecn-rejected", v4pkt, unix.VIRTIO_NET_HDR_GSO_UDP_L4 | unix.VIRTIO_NET_HDR_GSO_ECN, true},
|
|
{"tcpv4-plain-v4", v4pkt, unix.VIRTIO_NET_HDR_GSO_TCPV4, false},
|
|
{"tcpv4-plain-v6-mismatch", v6pkt, unix.VIRTIO_NET_HDR_GSO_TCPV4, true},
|
|
}
|
|
for _, tc := range cases {
|
|
t.Run(tc.name, func(t *testing.T) {
|
|
err := CheckValid(tc.pkt, NewHeader(0, tc.gsoType, 0, 100, 0, 0))
|
|
if tc.wantErr && err == nil {
|
|
t.Errorf("CheckValid(gsoType=%#x) = nil, want error", tc.gsoType)
|
|
}
|
|
if !tc.wantErr && err != nil {
|
|
t.Errorf("CheckValid(gsoType=%#x) = %v, want nil", tc.gsoType, err)
|
|
}
|
|
})
|
|
}
|
|
}
|
|
|
|
// TestCheckValidRejectsZeroGSOSize: a GSO-typed header with gso_size=0 must be
|
|
// rejected. It would produce a Packet whose GSOInfo.IsSuperpacket() is false,
|
|
// dodging both segmentation and FinishChecksum on its way downstream.
|
|
func TestCheckValidRejectsZeroGSOSize(t *testing.T) {
|
|
v4pkt, _, _ := buildTCPv4Super(100)
|
|
if err := CheckValid(v4pkt, NewHeader(0, unix.VIRTIO_NET_HDR_GSO_TCPV4, 0, 0, 0, 0)); err == nil {
|
|
t.Fatal("CheckValid accepted a GSO-typed header with gso_size=0")
|
|
}
|
|
}
|
|
|
|
// TestFoldComplementMatchesReference checks the segmenter's fold-and-invert
|
|
// against an independent RFC 1071 reference fold, hitting the carry edge
|
|
// cases (values whose first fold produces another carry).
|
|
func TestFoldComplementMatchesReference(t *testing.T) {
|
|
refFold := func(s uint64) uint16 {
|
|
for s>>16 != 0 {
|
|
s = s&0xffff + s>>16
|
|
}
|
|
return uint16(s)
|
|
}
|
|
cases := []uint32{
|
|
0, 1, 0xffff,
|
|
0x10000, // single carry
|
|
0x1fffe, // 0xffff + 0xffff: carry produces another 0xffff
|
|
0xffff0000, // high half only
|
|
0xfffeffff, // first fold yields another carry
|
|
0xffffffff, // worst case
|
|
}
|
|
for _, c := range cases {
|
|
if got, want := foldComplement(c), ^refFold(uint64(c)); got != want {
|
|
t.Errorf("foldComplement(%#x) = %#x, want %#x", c, got, want)
|
|
}
|
|
}
|
|
}
|
|
|
|
// referenceBaseIPv4HdrSum and referenceBaseTCPHdrSum are the straightforward
|
|
// implementations that baseIPv4HdrSum/baseTCPHdrSum replaced: copy the header
|
|
// into scratch, zero the fields the segment loop rewrites, sum. The production
|
|
// versions instead sum in place and subtract those fields via one's-complement
|
|
// arithmetic, which is faster but far less obvious — particularly for the TCP
|
|
// flags byte, which is only half of a 16-bit word. These references exist so
|
|
// that trade is checked rather than asserted.
|
|
func referenceBaseIPv4HdrSum(pkt []byte, ihl int) uint32 {
|
|
var ipTmp [ipv4HeaderMaxLen]byte
|
|
copy(ipTmp[:ihl], pkt[:ihl])
|
|
ipTmp[ipv4TotalLenOff], ipTmp[ipv4TotalLenOff+1] = 0, 0
|
|
ipTmp[ipv4ChecksumOff], ipTmp[ipv4ChecksumOff+1] = 0, 0
|
|
ipTmp[ipv4IDOff], ipTmp[ipv4IDOff+1] = 0, 0
|
|
return uint32(checksum.Checksum(ipTmp[:ihl], 0))
|
|
}
|
|
|
|
func referenceBaseTCPHdrSum(pkt []byte, csumStart, headerLen int) uint32 {
|
|
tcpLen := headerLen - csumStart
|
|
var tmp [tcpHeaderMaxLen]byte
|
|
copy(tmp[:tcpLen], pkt[csumStart:headerLen])
|
|
tmp[tcpSeqOff], tmp[tcpSeqOff+1], tmp[tcpSeqOff+2], tmp[tcpSeqOff+3] = 0, 0, 0, 0
|
|
tmp[tcpFlagsOff] = 0
|
|
tmp[tcpChecksumOff], tmp[tcpChecksumOff+1] = 0, 0
|
|
return uint32(checksum.Checksum(tmp[:tcpLen], 0))
|
|
}
|
|
|
|
// randSeed is a tiny deterministic PRNG so this test needs no imports beyond
|
|
// what the file already has and reproduces identically on every run.
|
|
func randByte(state *uint32) byte {
|
|
*state = *state*1664525 + 1013904223
|
|
return byte(*state >> 24)
|
|
}
|
|
|
|
func TestBaseSumsMatchZeroingReference(t *testing.T) {
|
|
state := uint32(12345)
|
|
|
|
t.Run("ipv4", func(t *testing.T) {
|
|
for ihl := ipv4HeaderMinLen; ihl <= ipv4HeaderMaxLen; ihl += 4 {
|
|
for iter := 0; iter < 5000; iter++ {
|
|
pkt := make([]byte, ihl)
|
|
for i := range pkt {
|
|
pkt[i] = randByte(&state)
|
|
}
|
|
pkt[0] = byte(0x40 | (ihl / 4))
|
|
|
|
want := referenceBaseIPv4HdrSum(pkt, ihl)
|
|
got, err := baseIPv4HdrSum(pkt, ihl)
|
|
if err != nil {
|
|
t.Fatalf("ihl=%d: %v", ihl, err)
|
|
}
|
|
// Compare the value that reaches the wire: the raw partial
|
|
// sums may legally differ by one's-complement -0 vs +0.
|
|
for _, tl := range []uint32{20, 1500, 65535} {
|
|
for _, id := range []uint32{0, 0x4242, 0xffff} {
|
|
if a, b := foldComplement(want+tl+id), foldComplement(got+tl+id); a != b {
|
|
t.Fatalf("ihl=%d tl=%d id=%d: %#04x != %#04x", ihl, tl, id, a, b)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
})
|
|
|
|
t.Run("tcp", func(t *testing.T) {
|
|
const csumStart = 20
|
|
for dataOff := 5; dataOff <= 15; dataOff++ {
|
|
tcpLen := dataOff * 4
|
|
headerLen := csumStart + tcpLen
|
|
for iter := 0; iter < 5000; iter++ {
|
|
pkt := make([]byte, headerLen+64)
|
|
for i := range pkt {
|
|
pkt[i] = randByte(&state)
|
|
}
|
|
pkt[0] = 0x45
|
|
pkt[csumStart+tcpDataOffOff] = byte(dataOff << 4)
|
|
|
|
want := referenceBaseTCPHdrSum(pkt, csumStart, headerLen)
|
|
got := baseTCPHdrSum(pkt, csumStart, headerLen)
|
|
for _, seq := range []uint32{0, 1, 0x4242_4242, 0xffff_ffff} {
|
|
for _, fl := range []uint32{0x00, 0x10, 0x18, 0x19, 0xff} {
|
|
for _, l4 := range []uint32{20, 1460, 65535} {
|
|
a := foldComplement(want + seq + fl + l4)
|
|
b := foldComplement(got + seq + fl + l4)
|
|
if a != b {
|
|
t.Fatalf("dataOff=%d seq=%#x fl=%#x l4=%d: %#04x != %#04x",
|
|
dataOff, seq, fl, l4, a, b)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
})
|
|
}
|