package overlay
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"net"
"net/netip"
"testing"
"time"
"golang.org/x/net/bpf"
"golang.org/x/net/ipv4"
"golang.org/x/sys/unix"
)
func TestVNIMatchBPF(t *testing.T) {
// The BPF filter program under test uses Linux extensions which are not
// emulated by any user-space BPF interpreters. It is also classic BPF,
// which cannot be tested in-kernel using the bpf(BPF_PROG_RUN) syscall.
// The best we can do without actually programming it into an iptables
// rule and end-to-end testing it is to attach it as a socket filter to
// a raw socket and test which loopback packets make it through.
//
// Modern kernels transpile cBPF programs into eBPF for execution, so a
// possible future direction would be to extract the transpiler and
// convert the program under test to eBPF so it could be loaded and run
// using the bpf(2) syscall.
// https://elixir.bootlin.com/linux/v6.2/source/net/core/filter.c#L559
// Though the effort would be better spent on adding nftables support to
// libnetwork so this whole BPF program could be replaced with a native
// nftables '@th' match expression.
//
// The filter could be manually e2e-tested for both IPv4 and IPv6 by
// programming ip[6]tables rules which log matching packets and sending
// test packets loopback using netcat. All the necessary information
// (bytecode and an acceptable test vector) is logged by this test.
//
// $ sudo ip6tables -A INPUT -p udp -s ::1 -d ::1 -m bpf \
// --bytecode "${bpf_program_under_test}" \
// -j LOG --log-prefix '[IPv6 VNI match]:'
// $ <<<"${udp_payload_hexdump}" xxd -r -p | nc -u -6 localhost 30000
// $ sudo dmesg
loopback := net.IPv4(127, 0, 0, 1)
// Reserve an ephemeral UDP port for loopback testing.
// Binding to a TUN device would be more hermetic, but is much more effort to set up.
reservation, err := net.ListenUDP("udp", &net.UDPAddr{IP: loopback, Port: 0})
if err != nil {
t.Fatal(err)
}
defer reservation.Close()
daddr := reservation.LocalAddr().(*net.UDPAddr).AddrPort()
sender, err := net.DialUDP("udp", nil, reservation.LocalAddr().(*net.UDPAddr))
if err != nil {
t.Fatal(err)
}
defer sender.Close()
saddr := sender.LocalAddr().(*net.UDPAddr).AddrPort()
// There doesn't seem to be a way to receive the entire Layer-3 IPv6
// packet including the fixed IP header using the portable raw sockets
// API. That can only be done from an AF_PACKET socket, and it is
// unclear whether 'ld poff' would behave the same in a BPF program
// attached to such a socket as in an xt_bpf match.
c, err := net.ListenIP("ip4:udp", &net.IPAddr{IP: loopback})
if err != nil {
if errors.Is(err, unix.EPERM) {
t.Skip("test requires CAP_NET_RAW")
}
t.Fatal(err)
}
defer c.Close()
pc := ipv4.NewPacketConn(c)
testvectors := []uint32{
0,
1,
0x08,
42,
0x80,
0xfe,
0xff,
0x100,
0xfff, // 4095
0x1000, // 4096
0x1001,
0x10000,
0xfffffe,
0xffffff, // Max VNI
}
for _, vni := range []uint32{1, 42, 0x100, 0x1000, 0xfffffe, 0xffffff} {
t.Run(fmt.Sprintf("vni=%d", vni), func(t *testing.T) {
setBPF(t, pc, vniMatchBPF(vni))
for _, v := range testvectors {
pkt := appendVXLANHeader(nil, v)
pkt = append(pkt, []byte{0xde, 0xad, 0xbe, 0xef}...)
if _, err := sender.Write(pkt); err != nil {
t.Fatal(err)
}
rpkt, ok := readUDPPacketFromRawSocket(t, pc, saddr, daddr)
// Sanity check: the only packets readUDPPacketFromRawSocket
// should return are ones we sent.
if ok && !bytes.Equal(pkt, rpkt) {
t.Fatalf("received unexpected packet: % x", rpkt)
}
if ok != (v == vni) {
t.Errorf("unexpected packet tagged with vni=%d (got %v, want %v)", v, ok, v == vni)
}
}
})
}
}
func appendVXLANHeader(b []byte, vni uint32) []byte {
// https://tools.ietf.org/html/rfc7348#section-5
b = append(b, []byte{0x08, 0x00, 0x00, 0x00}...)
return binary.BigEndian.AppendUint32(b, vni<<8)
}
func setBPF(t *testing.T, c *ipv4.PacketConn, fprog []bpf.RawInstruction) {
// https://natanyellin.com/posts/ebpf-filtering-done-right/
blockall, _ := bpf.Assemble([]bpf.Instruction{bpf.RetConstant{Val: 0}})
if err := c.SetBPF(blockall); err != nil {
t.Fatal(err)
}
ms := make([]ipv4.Message, 100)
for {
n, err := c.ReadBatch(ms, unix.MSG_DONTWAIT)
if err != nil {
if errors.Is(err, unix.EAGAIN) {
break
}
t.Fatal(err)
}
if n == 0 {
break
}
}
t.Logf("setting socket filter: %v", marshalXTBPF(fprog))
if err := c.SetBPF(fprog); err != nil {
t.Fatal(err)
}
}
// readUDPPacketFromRawSocket reads raw IP packets from pc until a UDP packet
// which matches the (src, dst) 4-tuple is found or the receive buffer is empty,
// and returns the payload of the UDP packet.
func readUDPPacketFromRawSocket(t *testing.T, pc *ipv4.PacketConn, src, dst netip.AddrPort) ([]byte, bool) {
t.Helper()
ms := []ipv4.Message{
{Buffers: [][]byte{make([]byte, 1500)}},
}
// Set a time limit to prevent an infinite loop if there is a lot of
// loopback traffic being captured which prevents the buffer from
// emptying.
deadline := time.Now().Add(1 * time.Second)
for time.Now().Before(deadline) {
n, err := pc.ReadBatch(ms, unix.MSG_DONTWAIT)
if err != nil {
if !errors.Is(err, unix.EAGAIN) {
t.Fatal(err)
}
break
}
if n == 0 {
break
}
pkt := ms[0].Buffers[0][:ms[0].N]
psrc, pdst, payload, ok := parseUDP(pkt)
// Discard captured packets which belong to other unrelated flows.
if !ok || psrc != src || pdst != dst {
t.Logf("discarding packet:\n% x", pkt)
continue
}
t.Logf("received packet (%v -> %v):\n% x", psrc, pdst, payload)
// While not strictly required, copy payload into a new
// slice which does not share a backing array with pkt
// so the IP and UDP headers can be garbage collected.
return append([]byte(nil), payload...), true
}
return nil, false
}
func parseIPv4(b []byte) (src, dst netip.Addr, protocol byte, payload []byte, ok bool) {
if len(b) < 20 {
return netip.Addr{}, netip.Addr{}, 0, nil, false
}
hlen := int(b[0]&0x0f) * 4
if hlen < 20 {
return netip.Addr{}, netip.Addr{}, 0, nil, false
}
src, _ = netip.AddrFromSlice(b[12:16])
dst, _ = netip.AddrFromSlice(b[16:20])
protocol = b[9]
payload = b[hlen:]
return src, dst, protocol, payload, true
}
// parseUDP parses the IP and UDP headers from the raw Layer-3 packet data in b.
func parseUDP(b []byte) (src, dst netip.AddrPort, payload []byte, ok bool) {
srcip, dstip, protocol, ippayload, ok := parseIPv4(b)
if !ok {
return netip.AddrPort{}, netip.AddrPort{}, nil, false
}
if protocol != 17 {
return netip.AddrPort{}, netip.AddrPort{}, nil, false
}
if len(ippayload) < 8 {
return netip.AddrPort{}, netip.AddrPort{}, nil, false
}
sport := binary.BigEndian.Uint16(ippayload[0:2])
dport := binary.BigEndian.Uint16(ippayload[2:4])
src = netip.AddrPortFrom(srcip, sport)
dst = netip.AddrPortFrom(dstip, dport)
payload = ippayload[8:]
return src, dst, payload, true
}