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Egress tunnel capture + agent identity #338
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Nina Polshakova (npolshakova)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,140 @@ | ||
| //go:build linux | ||
|
|
||
| // Copyright 2026 Google LLC | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
||
| package main | ||
|
|
||
| import ( | ||
| "context" | ||
| "encoding/binary" | ||
| "fmt" | ||
| "net" | ||
| "syscall" | ||
| "unsafe" | ||
|
|
||
| "github.com/agent-substrate/substrate/internal/egresscapture" | ||
| "github.com/google/nftables" | ||
| "github.com/google/nftables/binaryutil" | ||
| "github.com/google/nftables/expr" | ||
| "golang.org/x/sys/unix" | ||
| ) | ||
|
|
||
| const ( | ||
| egressCaptureHTTPPort = uint16(15001) | ||
| egressCaptureHTTPSPort = uint16(15002) | ||
| egressOriginalHTTPPort = uint16(80) | ||
| egressOriginalHTTPSPort = uint16(443) | ||
| ) | ||
|
|
||
| var defaultEgressCaptureRedirects = []struct { | ||
| originalPort uint16 | ||
| capturePort uint16 | ||
| }{ | ||
| {originalPort: egressOriginalHTTPPort, capturePort: egressCaptureHTTPPort}, | ||
| {originalPort: egressOriginalHTTPSPort, capturePort: egressCaptureHTTPSPort}, | ||
| } | ||
|
|
||
| var defaultEgressCaptureListeners = []egresscapture.Listener{ | ||
| {Port: egressCaptureHTTPPort}, | ||
| {Port: egressCaptureHTTPSPort}, | ||
| } | ||
|
|
||
| func (s *AteomService) startEgressCaptureIfEnabled(ctx context.Context, identity egresscapture.ActorIdentity) error { | ||
| if !egresscapture.EnabledFromEnv() { | ||
| return nil | ||
| } | ||
| cfg, err := egresscapture.ConfigFromEnv(defaultEgressCaptureListeners) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| capture, err := egresscapture.Start(ctx, identity, cfg, originalDestination) | ||
| if err != nil { | ||
| return fmt.Errorf("while starting actor egress capture: %w", err) | ||
| } | ||
| s.egressCapture = capture | ||
| return nil | ||
| } | ||
|
|
||
| func addEgressCaptureRedirectRules(c *nftables.Conn, table *nftables.Table, prerouting *nftables.Chain, sourceIP string) { | ||
| for _, redirect := range defaultEgressCaptureRedirects { | ||
| c.AddRule(&nftables.Rule{ | ||
| Table: table, | ||
| Chain: prerouting, | ||
| Exprs: tcpRedirectExprs(sourceIP, redirect.originalPort, redirect.capturePort), | ||
| }) | ||
| } | ||
| } | ||
|
|
||
| func tcpRedirectExprs(sourceIP string, originalPort, capturePort uint16) []expr.Any { | ||
| exprs := append(ipSourceEqual(sourceIP), tcpDestinationPortEqual(originalPort)...) | ||
| exprs = append(exprs, | ||
| &expr.Immediate{ | ||
| Register: 1, | ||
| Data: binaryutil.BigEndian.PutUint16(capturePort), | ||
| }, | ||
| &expr.Redir{ | ||
| RegisterProtoMin: 1, | ||
| }, | ||
| ) | ||
| return exprs | ||
| } | ||
|
|
||
| func originalDestination(conn net.Conn) (net.Addr, error) { | ||
| tcpConn, ok := conn.(*net.TCPConn) | ||
| if !ok { | ||
| return nil, fmt.Errorf("captured connection is %T, not *net.TCPConn", conn) | ||
| } | ||
|
|
||
| rawConn, err := tcpConn.SyscallConn() | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
|
||
| var addr *net.TCPAddr | ||
| var controlErr error | ||
| if err := rawConn.Control(func(fd uintptr) { | ||
| addr, controlErr = originalDstFromFD(int(fd)) | ||
| }); err != nil { | ||
| return nil, err | ||
| } | ||
| if controlErr != nil { | ||
| return nil, controlErr | ||
| } | ||
| return addr, nil | ||
| } | ||
|
|
||
| func originalDstFromFD(fd int) (*net.TCPAddr, error) { | ||
| var raw unix.RawSockaddrInet4 | ||
| size := uint32(unsafe.Sizeof(raw)) | ||
| _, _, errno := unix.Syscall6( | ||
| unix.SYS_GETSOCKOPT, | ||
| uintptr(fd), | ||
| uintptr(unix.SOL_IP), | ||
| uintptr(unix.SO_ORIGINAL_DST), | ||
| uintptr(unsafe.Pointer(&raw)), | ||
| uintptr(unsafe.Pointer(&size)), | ||
| 0, | ||
| ) | ||
| if errno != 0 { | ||
| return nil, errno | ||
| } | ||
| if raw.Family != syscall.AF_INET { | ||
| return nil, fmt.Errorf("SO_ORIGINAL_DST returned address family %d", raw.Family) | ||
| } | ||
| return &net.TCPAddr{ | ||
| IP: net.IPv4(raw.Addr[0], raw.Addr[1], raw.Addr[2], raw.Addr[3]), | ||
| Port: int(binary.BigEndian.Uint16((*[2]byte)(unsafe.Pointer(&raw.Port))[:])), | ||
| }, nil | ||
| } | ||
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Why do you need to capture HTTP vs HTTPS separately? A single listener could handle both and since SO_ORIGINAL_DST is used anyway to lookup the original port in
deriveConnectAuthority.