mirror of
https://github.com/slackhq/nebula.git
synced 2026-08-15 20:27:03 +02:00
JackDoan
336 lines
12 KiB
Go
336 lines
12 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 := Hdr{
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Flags: unix.VIRTIO_NET_HDR_F_NEEDS_CSUM,
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GSOType: unix.VIRTIO_NET_HDR_GSO_UDP_L4,
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GSOSize: 6, // two 6-byte segments
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CsumStart: csumStart,
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CsumOffset: 6,
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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 := Hdr{
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Flags: unix.VIRTIO_NET_HDR_F_NEEDS_CSUM,
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GSOType: unix.VIRTIO_NET_HDR_GSO_UDP_L4,
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GSOSize: 6,
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CsumStart: 20,
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CsumOffset: 6,
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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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// UDP-GSO keeps the same IPv4 ID across every segment.
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if id := binary.BigEndian.Uint16(seg[4:6]); id != 0x4242 {
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t.Errorf("seg %d: ip id=%#x want 0x4242", i, id)
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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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