Merge pull request #45308 from corhere/libnet/overlay-bpf-ipv6
libnetwork/drivers/overlay: make VNI matcher IPv6-compatible
This commit is contained in:
Sebastiaan van Stijn
GitHub
commit
214e200f95
2 changed files with 240 additions and 10 deletions
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@ -8,18 +8,21 @@ import (
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"golang.org/x/net/bpf"
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)
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// vniMatchBPF returns a BPF program suitable for passing to the iptables bpf
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// match which matches on the VXAN Network ID of encapsulated packets. The
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// program assumes that it will be used in a rule which only matches UDP
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// datagrams.
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// vniMatchBPF returns a BPF program suitable for passing to the iptables and
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// ip6tables bpf match which matches on the VXAN Network ID of encapsulated
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// packets. The program assumes that it will be used in a rule which only
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// matches UDP datagrams.
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func vniMatchBPF(vni uint32) []bpf.RawInstruction {
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asm, err := bpf.Assemble([]bpf.Instruction{
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bpf.LoadMemShift{Off: 0}, // ldx 4*([0] & 0xf) ; Load length of IPv4 header into X
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bpf.LoadIndirect{Off: 12, Size: 4}, // ld [x + 12] ; Load VXLAN ID (UDP header + 4 bytes) into A
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bpf.ALUOpConstant{Op: bpf.ALUOpAnd, Val: 0xffffff00}, // and #0xffffff00 ; VXLAN ID is in top 24 bits
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bpf.JumpIf{Cond: bpf.JumpEqual, Val: vni << 8, SkipTrue: 1}, // jeq ($vni << 8), match
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bpf.RetConstant{Val: 0}, // ret #0
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bpf.RetConstant{Val: ^uint32(0)}, // match: ret #-1
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// Load offset of UDP payload into X.
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bpf.LoadExtension{Num: bpf.ExtPayloadOffset}, // ld poff
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bpf.TAX{}, // tax
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bpf.LoadIndirect{Off: 4, Size: 4}, // ld [x + 4] ; Load VXLAN ID into top 24 bits of A
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bpf.ALUOpConstant{Op: bpf.ALUOpShiftRight, Val: 8}, // rsh #8 ; A >>= 8
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bpf.JumpIf{Cond: bpf.JumpEqual, Val: vni, SkipTrue: 1}, // jeq $vni, match
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bpf.RetConstant{Val: 0}, // ret #0
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bpf.RetConstant{Val: ^uint32(0)}, // match: ret #-1
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})
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// bpf.Assemble() only errors if an instruction is invalid. As the only variable
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// part of the program is an instruction value for which the entire range is
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227
libnetwork/drivers/overlay/bpf_linux_test.go
Normal file
227
libnetwork/drivers/overlay/bpf_linux_test.go
Normal file
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@ -0,0 +1,227 @@
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package overlay
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import (
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"bytes"
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"encoding/binary"
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"errors"
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"fmt"
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"net"
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"net/netip"
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"testing"
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"time"
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"golang.org/x/net/bpf"
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"golang.org/x/net/ipv4"
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"golang.org/x/sys/unix"
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)
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func TestVNIMatchBPF(t *testing.T) {
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// The BPF filter program under test uses Linux extensions which are not
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// emulated by any user-space BPF interpreters. It is also classic BPF,
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// which cannot be tested in-kernel using the bpf(BPF_PROG_RUN) syscall.
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// The best we can do without actually programming it into an iptables
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// rule and end-to-end testing it is to attach it as a socket filter to
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// a raw socket and test which loopback packets make it through.
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//
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// Modern kernels transpile cBPF programs into eBPF for execution, so a
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// possible future direction would be to extract the transpiler and
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// convert the program under test to eBPF so it could be loaded and run
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// using the bpf(2) syscall.
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// https://elixir.bootlin.com/linux/v6.2/source/net/core/filter.c#L559
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// Though the effort would be better spent on adding nftables support to
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// libnetwork so this whole BPF program could be replaced with a native
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// nftables '@th' match expression.
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//
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// The filter could be manually e2e-tested for both IPv4 and IPv6 by
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// programming ip[6]tables rules which log matching packets and sending
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// test packets loopback using netcat. All the necessary information
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// (bytecode and an acceptable test vector) is logged by this test.
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//
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// $ sudo ip6tables -A INPUT -p udp -s ::1 -d ::1 -m bpf \
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// --bytecode "${bpf_program_under_test}" \
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// -j LOG --log-prefix '[IPv6 VNI match]:'
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// $ <<<"${udp_payload_hexdump}" xxd -r -p | nc -u -6 localhost 30000
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// $ sudo dmesg
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loopback := net.IPv4(127, 0, 0, 1)
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// Reserve an ephemeral UDP port for loopback testing.
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// Binding to a TUN device would be more hermetic, but is much more effort to set up.
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reservation, err := net.ListenUDP("udp", &net.UDPAddr{IP: loopback, Port: 0})
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if err != nil {
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t.Fatal(err)
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}
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defer reservation.Close()
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daddr := reservation.LocalAddr().(*net.UDPAddr).AddrPort()
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sender, err := net.DialUDP("udp", nil, reservation.LocalAddr().(*net.UDPAddr))
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if err != nil {
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t.Fatal(err)
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}
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defer sender.Close()
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saddr := sender.LocalAddr().(*net.UDPAddr).AddrPort()
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// There doesn't seem to be a way to receive the entire Layer-3 IPv6
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// packet including the fixed IP header using the portable raw sockets
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// API. That can only be done from an AF_PACKET socket, and it is
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// unclear whether 'ld poff' would behave the same in a BPF program
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// attached to such a socket as in an xt_bpf match.
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c, err := net.ListenIP("ip4:udp", &net.IPAddr{IP: loopback})
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if err != nil {
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if errors.Is(err, unix.EPERM) {
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t.Skip("test requires CAP_NET_RAW")
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}
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t.Fatal(err)
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}
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defer c.Close()
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pc := ipv4.NewPacketConn(c)
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testvectors := []uint32{
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0,
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1,
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0x08,
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42,
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0x80,
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0xfe,
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0xff,
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0x100,
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0xfff, // 4095
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0x1000, // 4096
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0x1001,
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0x10000,
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0xfffffe,
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0xffffff, // Max VNI
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}
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for _, vni := range []uint32{1, 42, 0x100, 0x1000, 0xfffffe, 0xffffff} {
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t.Run(fmt.Sprintf("vni=%d", vni), func(t *testing.T) {
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setBPF(t, pc, vniMatchBPF(vni))
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for _, v := range testvectors {
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pkt := appendVXLANHeader(nil, v)
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pkt = append(pkt, []byte{0xde, 0xad, 0xbe, 0xef}...)
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if _, err := sender.Write(pkt); err != nil {
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t.Fatal(err)
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}
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rpkt, ok := readUDPPacketFromRawSocket(t, pc, saddr, daddr)
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// Sanity check: the only packets readUDPPacketFromRawSocket
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// should return are ones we sent.
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if ok && !bytes.Equal(pkt, rpkt) {
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t.Fatalf("received unexpected packet: % x", rpkt)
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}
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if ok != (v == vni) {
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t.Errorf("unexpected packet tagged with vni=%d (got %v, want %v)", v, ok, v == vni)
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}
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}
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})
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}
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}
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func appendVXLANHeader(b []byte, vni uint32) []byte {
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// https://tools.ietf.org/html/rfc7348#section-5
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b = append(b, []byte{0x08, 0x00, 0x00, 0x00}...)
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return binary.BigEndian.AppendUint32(b, vni<<8)
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}
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func setBPF(t *testing.T, c *ipv4.PacketConn, fprog []bpf.RawInstruction) {
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// https://natanyellin.com/posts/ebpf-filtering-done-right/
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blockall, _ := bpf.Assemble([]bpf.Instruction{bpf.RetConstant{Val: 0}})
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if err := c.SetBPF(blockall); err != nil {
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t.Fatal(err)
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}
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ms := make([]ipv4.Message, 100)
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for {
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n, err := c.ReadBatch(ms, unix.MSG_DONTWAIT)
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if err != nil {
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if errors.Is(err, unix.EAGAIN) {
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break
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}
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t.Fatal(err)
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}
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if n == 0 {
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break
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}
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}
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t.Logf("setting socket filter: %v", marshalXTBPF(fprog))
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if err := c.SetBPF(fprog); err != nil {
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t.Fatal(err)
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}
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}
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// readUDPPacketFromRawSocket reads raw IP packets from pc until a UDP packet
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// which matches the (src, dst) 4-tuple is found or the receive buffer is empty,
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// and returns the payload of the UDP packet.
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func readUDPPacketFromRawSocket(t *testing.T, pc *ipv4.PacketConn, src, dst netip.AddrPort) ([]byte, bool) {
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t.Helper()
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ms := []ipv4.Message{
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{Buffers: [][]byte{make([]byte, 1500)}},
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}
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// Set a time limit to prevent an infinite loop if there is a lot of
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// loopback traffic being captured which prevents the buffer from
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// emptying.
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deadline := time.Now().Add(1 * time.Second)
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for time.Now().Before(deadline) {
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n, err := pc.ReadBatch(ms, unix.MSG_DONTWAIT)
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if err != nil {
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if !errors.Is(err, unix.EAGAIN) {
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t.Fatal(err)
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}
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break
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}
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if n == 0 {
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break
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}
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pkt := ms[0].Buffers[0][:ms[0].N]
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psrc, pdst, payload, ok := parseUDP(pkt)
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// Discard captured packets which belong to other unrelated flows.
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if !ok || psrc != src || pdst != dst {
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t.Logf("discarding packet:\n% x", pkt)
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continue
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}
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t.Logf("received packet (%v -> %v):\n% x", psrc, pdst, payload)
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// While not strictly required, copy payload into a new
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// slice which does not share a backing array with pkt
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// so the IP and UDP headers can be garbage collected.
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return append([]byte(nil), payload...), true
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}
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return nil, false
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}
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func parseIPv4(b []byte) (src, dst netip.Addr, protocol byte, payload []byte, ok bool) {
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if len(b) < 20 {
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return netip.Addr{}, netip.Addr{}, 0, nil, false
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}
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hlen := int(b[0]&0x0f) * 4
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if hlen < 20 {
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return netip.Addr{}, netip.Addr{}, 0, nil, false
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}
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src, _ = netip.AddrFromSlice(b[12:16])
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dst, _ = netip.AddrFromSlice(b[16:20])
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protocol = b[9]
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payload = b[hlen:]
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return src, dst, protocol, payload, true
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}
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// parseUDP parses the IP and UDP headers from the raw Layer-3 packet data in b.
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func parseUDP(b []byte) (src, dst netip.AddrPort, payload []byte, ok bool) {
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srcip, dstip, protocol, ippayload, ok := parseIPv4(b)
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if !ok {
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return netip.AddrPort{}, netip.AddrPort{}, nil, false
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}
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if protocol != 17 {
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return netip.AddrPort{}, netip.AddrPort{}, nil, false
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}
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if len(ippayload) < 8 {
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return netip.AddrPort{}, netip.AddrPort{}, nil, false
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}
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sport := binary.BigEndian.Uint16(ippayload[0:2])
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dport := binary.BigEndian.Uint16(ippayload[2:4])
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src = netip.AddrPortFrom(srcip, sport)
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dst = netip.AddrPortFrom(dstip, dport)
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payload = ippayload[8:]
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return src, dst, payload, true
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}
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