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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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35
wgengine/capture/capture.go
View File

@@ -15,6 +15,7 @@ import (
_ "embed"
"tailscale.com/net/packet"
"tailscale.com/util/set"
)
@@ -26,7 +27,7 @@ var DissectorLua string
// 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
View File

@@ -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