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net, wgengine/capture: encode NAT addresses in pcap stream

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Signed-off-by: Tom DNetto <tom@tailscale.com>
This commit is contained in:
Tom DNetto 2023-03-30 12:39:39 -07:00 committed by Tom
parent 92459a9248
commit 6a627e5a33
7 changed files with 94 additions and 28 deletions
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2
cmd/tailscale/depaware.txt
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@ -76,7 +76,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
tailscale.com/net/netknob from tailscale.com/net/netns
tailscale.com/net/netns from tailscale.com/derp/derphttp+
tailscale.com/net/netutil from tailscale.com/client/tailscale+
tailscale.com/net/packet from tailscale.com/wgengine/filter
tailscale.com/net/packet from tailscale.com/wgengine/filter+
tailscale.com/net/ping from tailscale.com/net/netcheck
tailscale.com/net/portmapper from tailscale.com/net/netcheck+
tailscale.com/net/sockstats from tailscale.com/control/controlhttp+

17
net/packet/packet.go
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@ -34,6 +34,14 @@
TCPECNBits TCPFlag = TCPECNEcho | TCPCWR
)
// CaptureMeta contains metadata that is used when debugging.
type CaptureMeta struct {
DidSNAT bool // SNAT was performed & the address was updated.
OriginalSrc netip.AddrPort // The source address before SNAT was performed.
DidDNAT bool // DNAT was performed & the address was updated.
OriginalDst netip.AddrPort // The destination address before DNAT was performed.
}
// Parsed is a minimal decoding of a packet suitable for use in filters.
type Parsed struct {
// b is the byte buffer that this decodes.
@ -58,6 +66,9 @@ type Parsed struct {
Dst netip.AddrPort
// TCPFlags is the packet's TCP flag bits. Valid iff IPProto == TCP.
TCPFlags TCPFlag
// CaptureMeta contains metadata that is used when debugging.
CaptureMeta CaptureMeta
}
func (p *Parsed) String() string {
@ -84,6 +95,7 @@ func (p *Parsed) String() string {
// and shouldn't need any memory allocation.
func (q *Parsed) Decode(b []byte) {
q.b = b
q.CaptureMeta = CaptureMeta{} // Clear any capture metadata if it exists.
if len(b) < 1 {
q.IPVersion = 0
@ -447,6 +459,8 @@ func (q *Parsed) UpdateSrcAddr(src netip.Addr) {
if q.IPVersion != 4 || src.Is6() {
panic("UpdateSrcAddr: only IPv4 is supported")
}
q.CaptureMeta.DidSNAT = true
q.CaptureMeta.OriginalSrc = q.Src
old := q.Src.Addr()
q.Src = netip.AddrPortFrom(src, q.Src.Port())
@ -465,6 +479,9 @@ func (q *Parsed) UpdateDstAddr(dst netip.Addr) {
panic("UpdateDstAddr: only IPv4 is supported")
}
q.CaptureMeta.DidDNAT = true
q.CaptureMeta.OriginalDst = q.Dst
old := q.Dst.Addr()
q.Dst = netip.AddrPortFrom(dst, q.Dst.Port())

33
net/tstun/wrap.go
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@ -713,6 +713,7 @@ func (t *Wrapper) Read(buffs [][]byte, sizes []int, offset int) (int, error) {
var buffsPos int
p := parsedPacketPool.Get().(*packet.Parsed)
defer parsedPacketPool.Put(p)
captHook := t.captureHook.Load()
for _, data := range res.data {
p.Decode(data[res.dataOffset:])
@ -722,8 +723,8 @@ func (t *Wrapper) Read(buffs [][]byte, sizes []int, offset int) (int, error) {
fn()
}
}
if capt := t.captureHook.Load(); capt != nil {
capt(capture.FromLocal, time.Now(), p.Buffer())
if captHook != nil {
captHook(capture.FromLocal, time.Now(), p.Buffer(), p.CaptureMeta)
}
if !t.disableFilter {
response := t.filterPacketOutboundToWireGuard(p)
@ -788,9 +789,9 @@ func (t *Wrapper) injectedRead(res tunInjectedRead, buf []byte, offset int) (int
return n, nil
}
func (t *Wrapper) filterPacketInboundFromWireGuard(p *packet.Parsed) filter.Response {
if capt := t.captureHook.Load(); capt != nil {
capt(capture.FromPeer, time.Now(), p.Buffer())
func (t *Wrapper) filterPacketInboundFromWireGuard(p *packet.Parsed, captHook capture.Callback) filter.Response {
if captHook != nil {
captHook(capture.FromPeer, time.Now(), p.Buffer(), p.CaptureMeta)
}
if p.IPProto == ipproto.TSMP {
@ -892,11 +893,12 @@ func (t *Wrapper) Write(buffs [][]byte, offset int) (int, error) {
i := 0
p := parsedPacketPool.Get().(*packet.Parsed)
defer parsedPacketPool.Put(p)
captHook := t.captureHook.Load()
for _, buff := range buffs {
p.Decode(buff[offset:])
t.dnatV4(p)
if !t.disableFilter {
if t.filterPacketInboundFromWireGuard(p) != filter.Accept {
if t.filterPacketInboundFromWireGuard(p, captHook) != filter.Accept {
metricPacketInDrop.Add(1)
} else {
buffs[i] = buff
@ -955,8 +957,9 @@ func (t *Wrapper) InjectInboundPacketBuffer(pkt stack.PacketBufferPtr) error {
p := parsedPacketPool.Get().(*packet.Parsed)
defer parsedPacketPool.Put(p)
p.Decode(buf[PacketStartOffset:])
if capt := t.captureHook.Load(); capt != nil {
capt(capture.SynthesizedToLocal, time.Now(), p.Buffer())
captHook := t.captureHook.Load()
if captHook != nil {
captHook(capture.SynthesizedToLocal, time.Now(), p.Buffer(), p.CaptureMeta)
}
t.dnatV4(p)
@ -1048,22 +1051,22 @@ func (t *Wrapper) InjectOutbound(packet []byte) error {
// InjectOutboundPacketBuffer logically behaves as InjectOutbound. It takes ownership of one
// reference count on the packet, and the packet may be mutated. The packet refcount will be
// decremented after the injected buffer has been read.
func (t *Wrapper) InjectOutboundPacketBuffer(packet stack.PacketBufferPtr) error {
size := packet.Size()
func (t *Wrapper) InjectOutboundPacketBuffer(pkt stack.PacketBufferPtr) error {
size := pkt.Size()
if size > MaxPacketSize {
packet.DecRef()
pkt.DecRef()
return errPacketTooBig
}
if size == 0 {
packet.DecRef()
pkt.DecRef()
return nil
}
if capt := t.captureHook.Load(); capt != nil {
b := packet.ToBuffer()
capt(capture.SynthesizedToPeer, time.Now(), b.Flatten())
b := pkt.ToBuffer()
capt(capture.SynthesizedToPeer, time.Now(), b.Flatten(), packet.CaptureMeta{})
}
t.injectOutbound(tunInjectedRead{packet: packet})
t.injectOutbound(tunInjectedRead{packet: pkt})
return nil
}

4
net/tstun/wrap_test.go
View File

@ -545,7 +545,7 @@ func TestPeerAPIBypass(t *testing.T) {
tt.w.SetFilter(tt.filter)
tt.w.disableTSMPRejected = true
tt.w.logf = t.Logf
if got := tt.w.filterPacketInboundFromWireGuard(p); got != tt.want {
if got := tt.w.filterPacketInboundFromWireGuard(p, nil); got != tt.want {
t.Errorf("got = %v; want %v", got, tt.want)
}
})
@ -575,7 +575,7 @@ func TestFilterDiscoLoop(t *testing.T) {
p := new(packet.Parsed)
p.Decode(pkt)
got := tw.filterPacketInboundFromWireGuard(p)
got := tw.filterPacketInboundFromWireGuard(p, nil)
if got != filter.DropSilently {
t.Errorf("got %v; want DropSilently", got)
}

35
wgengine/capture/capture.go
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@ -15,6 +15,7 @@
_ "embed"
"tailscale.com/net/packet"
"tailscale.com/util/set"
)
@ -26,7 +27,7 @@
// Such callbacks must not take ownership of the
// provided data slice: it may only copy out of it
// within the lifetime of the function.
type Callback func(Path, time.Time, []byte)
type Callback func(Path, time.Time, []byte, packet.CaptureMeta)
var bufferPool = sync.Pool{
New: func() any {
@ -159,24 +160,50 @@ func (s *Sink) WaitCh() <-chan struct{} {
return s.ctx.Done()
}
func customDataLen(meta packet.CaptureMeta) int {
length := 4
if meta.DidSNAT {
length += meta.OriginalSrc.Addr().BitLen() / 8
}
if meta.DidDNAT {
length += meta.OriginalDst.Addr().BitLen() / 8
}
return length
}
// LogPacket is called to insert a packet into the capture.
//
// This function does not take ownership of the provided data slice.
func (s *Sink) LogPacket(path Path, when time.Time, data []byte) {
func (s *Sink) LogPacket(path Path, when time.Time, data []byte, meta packet.CaptureMeta) {
select {
case <-s.ctx.Done():
return
default:
}
extraLen := customDataLen(meta)
b := bufferPool.Get().(*bytes.Buffer)
b.Reset()
b.Grow(16 + 2 + len(data)) // 16b pcap header + 2b custom data + len
b.Grow(16 + extraLen + len(data)) // 16b pcap header + len(metadata) + len(payload)
defer bufferPool.Put(b)
writePktHeader(b, when, len(data)+2)
writePktHeader(b, when, len(data)+extraLen)
// Custom tailscale debugging data
binary.Write(b, binary.LittleEndian, uint16(path))
if meta.DidSNAT {
binary.Write(b, binary.LittleEndian, uint8(meta.OriginalSrc.Addr().BitLen()/8))
b.Write(meta.OriginalSrc.Addr().AsSlice())
} else {
binary.Write(b, binary.LittleEndian, uint8(0)) // SNAT addr len == 0
}
if meta.DidDNAT {
binary.Write(b, binary.LittleEndian, uint8(meta.OriginalDst.Addr().BitLen()/8))
b.Write(meta.OriginalDst.Addr().AsSlice())
} else {
binary.Write(b, binary.LittleEndian, uint8(0)) // DNAT addr len == 0
}
b.Write(data)
s.mu.Lock()

28
wgengine/capture/ts-dissector.lua
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@ -4,7 +4,11 @@ end
tsdebug_ll = Proto("tsdebug", "Tailscale debug")
PATH = ProtoField.string("tsdebug.PATH","PATH", base.ASCII)
tsdebug_ll.fields = {PATH}
SNAT_IP_4 = ProtoField.ipv4("tsdebug.SNAT_IP_4", "Pre-NAT Source IPv4 address")
SNAT_IP_6 = ProtoField.ipv4("tsdebug.SNAT_IP_6", "Pre-NAT Source IPv6 address")
DNAT_IP_4 = ProtoField.ipv4("tsdebug.DNAT_IP_4", "Pre-NAT Dest IPv4 address")
DNAT_IP_6 = ProtoField.ipv4("tsdebug.DNAT_IP_6", "Pre-NAT Dest IPv6 address")
tsdebug_ll.fields = {PATH, SNAT_IP_4, SNAT_IP_6, DNAT_IP_4, DNAT_IP_6}
function tsdebug_ll.dissector(buffer, pinfo, tree)
pinfo.cols.protocol = tsdebug_ll.name
@ -14,14 +18,28 @@ function tsdebug_ll.dissector(buffer, pinfo, tree)
-- -- Get path UINT16
local path_id = buffer:range(offset, 2):le_uint()
if path_id == 0 then subtree:add(PATH, "FromLocal")
elseif path_id == 1 then subtree:add(PATH, "FromPeer")
elseif path_id == 2 then subtree:add(PATH, "Synthesized (Inbound / ToLocal)")
elseif path_id == 3 then subtree:add(PATH, "Synthesized (Outbound / ToPeer)")
if path_id == 0 then subtree:add(PATH, "FromLocal")
elseif path_id == 1 then subtree:add(PATH, "FromPeer")
elseif path_id == 2 then subtree:add(PATH, "Synthesized (Inbound / ToLocal)")
elseif path_id == 3 then subtree:add(PATH, "Synthesized (Outbound / ToPeer)")
elseif path_id == 254 then subtree:add(PATH, "Disco frame")
end
offset = offset + 2
-- -- Get SNAT address
local snat_addr_len = buffer:range(offset, 1):le_uint()
if snat_addr_len == 4 then subtree:add(SNAT_IP_4, buffer:range(offset + 1, snat_addr_len))
elseif snat_addr_len > 0 then subtree:add(SNAT_IP_6, buffer:range(offset + 1, snat_addr_len))
end
offset = offset + 1 + snat_addr_len
-- -- Get DNAT address
local dnat_addr_len = buffer:range(offset, 1):le_uint()
if dnat_addr_len == 4 then subtree:add(DNAT_IP_4, buffer:range(offset + 1, dnat_addr_len))
elseif dnat_addr_len > 0 then subtree:add(DNAT_IP_6, buffer:range(offset + 1, dnat_addr_len))
end
offset = offset + 1 + dnat_addr_len
-- -- Handover rest of data to lower-level dissector
local data_buffer = buffer:range(offset, packet_length-offset):tvb()
if path_id == 254 then

3
wgengine/magicsock/magicsock.go
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@ -47,6 +47,7 @@
"tailscale.com/net/netcheck"
"tailscale.com/net/neterror"
"tailscale.com/net/netns"
"tailscale.com/net/packet"
"tailscale.com/net/portmapper"
"tailscale.com/net/sockstats"
"tailscale.com/net/stun"
@ -2215,7 +2216,7 @@ func (c *Conn) handleDiscoMessage(msg []byte, src netip.AddrPort, derpNodeSrc ke
// Emit information about the disco frame into the pcap stream
// if a capture hook is installed.
if cb := c.captureHook.Load(); cb != nil {
cb(capture.PathDisco, time.Now(), discoPcapFrame(src, derpNodeSrc, payload))
cb(capture.PathDisco, time.Now(), discoPcapFrame(src, derpNodeSrc, payload), packet.CaptureMeta{})
}
dm, err := disco.Parse(payload)