forked from cloudflare/redoctober
/
server.go
274 lines (225 loc) · 6.03 KB
/
server.go
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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package roagent
import (
"encoding/binary"
"errors"
"fmt"
"io"
"log"
"golang.org/x/crypto/ssh"
)
const SSHROKey string = "ssh-ro"
var errLocked = errors.New("agent: locked")
// Server wraps an Agent and uses it to implement the agent side of
// the SSH-agent, wire protocol.
type server struct {
roagent *ROAgent
}
func parseROSigner(req []byte) (*AddedKey, error) {
var k roSignerMsg
if err := ssh.Unmarshal(req, &k); err != nil {
return nil, err
}
pubKey, err := ssh.ParsePublicKey(k.Pub)
if err != nil {
return nil, errors.New("received ill-formatted public key")
}
return &AddedKey{
PrivateKey: &ROSigner{
pub: pubKey,
encKey: k.EncKey,
},
Comment: k.Comments,
}, nil
}
func (s *server) insertIdentity(req []byte) error {
var record struct {
Type string `sshtype:"17|25"`
Rest []byte `ssh:"rest"`
}
// FIXME what is record?
if err := ssh.Unmarshal(req, &record); err != nil {
return err
}
var addedKey *AddedKey
var err error
if record.Type == SSHROKey {
addedKey, err = parseROSigner(req)
} else {
return errors.New("roagent can only accept keys encrypted by a Red October server")
}
if err != nil {
return err
}
return s.roagent.Add(*addedKey)
}
func (s *server) processRequestBytes(reqData []byte) []byte {
rep, err := s.processRequest(reqData)
if err != nil {
if err != errLocked {
// TODO(hanwen): provide better logging interface?
log.Printf("agent %d: %v", reqData[0], err)
}
return []byte{agentFailure}
}
if err == nil && rep == nil {
return []byte{agentSuccess}
}
return ssh.Marshal(rep)
}
func marshalKey(k *Key) []byte {
var record struct {
Blob []byte
Comment string
}
record.Blob = k.Marshal()
record.Comment = k.Comment
return ssh.Marshal(&record)
}
// See [PROTOCOL.agent], section 2.5.1.
const agentV1IdentitiesAnswer = 2
type agentV1IdentityMsg struct {
Numkeys uint32 `sshtype:"2"`
}
type agentRemoveIdentityMsg struct {
KeyBlob []byte `sshtype:"18"`
}
type agentLockMsg struct {
Passphrase []byte `sshtype:"22"`
}
type agentUnlockMsg struct {
Passphrase []byte `sshtype:"23"`
}
func (s *server) processRequest(data []byte) (interface{}, error) {
switch data[0] {
case agentRequestV1Identities:
return &agentV1IdentityMsg{0}, nil
case agentRemoveAllV1Identities:
return nil, nil
case agentRemoveIdentity:
var req agentRemoveIdentityMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
var wk wireKey
if err := ssh.Unmarshal(req.KeyBlob, &wk); err != nil {
return nil, err
}
return nil, s.roagent.Remove(&Key{Format: wk.Format, Blob: req.KeyBlob})
case agentRemoveAllIdentities:
return nil, s.roagent.RemoveAll()
case agentLock:
var req agentLockMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
return nil, s.roagent.Lock(req.Passphrase)
case agentUnlock:
var req agentUnlockMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
return nil, s.roagent.Unlock(req.Passphrase)
case agentSignRequest:
var req signRequestAgentMsg
if err := ssh.Unmarshal(data, &req); err != nil {
return nil, err
}
var wk wireKey
if err := ssh.Unmarshal(req.KeyBlob, &wk); err != nil {
return nil, err
}
k := &Key{
Format: wk.Format,
Blob: req.KeyBlob,
}
sig, err := s.roagent.Sign(k, req.Data) // TODO(hanwen): flags.
if err != nil {
return nil, err
}
return &signResponseAgentMsg{SigBlob: ssh.Marshal(sig)}, nil
case agentRequestIdentities:
keys, err := s.roagent.List()
if err != nil {
return nil, err
}
rep := identitiesAnswerAgentMsg{
NumKeys: uint32(len(keys)),
}
for _, k := range keys {
rep.Keys = append(rep.Keys, marshalKey(k)...)
}
return rep, nil
case agentAddIDConstrained, agentAddIdentity:
return nil, s.insertIdentity(data)
}
return nil, fmt.Errorf("unknown opcode %d", data[0])
}
func parseConstraints(constraints []byte) (lifetimeSecs uint32, confirmBeforeUse bool, extensions []ConstraintExtension, err error) {
for len(constraints) != 0 {
switch constraints[0] {
case agentConstrainLifetime:
lifetimeSecs = binary.BigEndian.Uint32(constraints[1:5])
constraints = constraints[5:]
case agentConstrainConfirm:
confirmBeforeUse = true
constraints = constraints[1:]
case agentConstrainExtension:
var msg constrainExtensionAgentMsg
if err = ssh.Unmarshal(constraints, &msg); err != nil {
return 0, false, nil, err
}
extensions = append(extensions, ConstraintExtension{
ExtensionName: msg.ExtensionName,
ExtensionDetails: msg.ExtensionDetails,
})
constraints = msg.Rest
default:
return 0, false, nil, fmt.Errorf("unknown constraint type: %d", constraints[0])
}
}
return
}
func setConstraints(key *AddedKey, constraintBytes []byte) error {
lifetimeSecs, confirmBeforeUse, constraintExtensions, err := parseConstraints(constraintBytes)
if err != nil {
return err
}
key.LifetimeSecs = lifetimeSecs
key.ConfirmBeforeUse = confirmBeforeUse
key.ConstraintExtensions = constraintExtensions
return nil
}
// ServeAgent serves the agent protocol on the given connection. It
// returns when an I/O error occurs.
func ServeAgent(roagent *ROAgent, c io.ReadWriter) error {
s := &server{roagent}
var length [4]byte
for {
if _, err := io.ReadFull(c, length[:]); err != nil {
return err
}
l := binary.BigEndian.Uint32(length[:])
if l > maxAgentResponseBytes {
// We also cap requests.
return fmt.Errorf("agent: request too large: %d", l)
}
req := make([]byte, l)
if _, err := io.ReadFull(c, req); err != nil {
return err
}
repData := s.processRequestBytes(req)
if len(repData) > maxAgentResponseBytes {
return fmt.Errorf("agent: reply too large: %d bytes", len(repData))
}
binary.BigEndian.PutUint32(length[:], uint32(len(repData)))
if _, err := c.Write(length[:]); err != nil {
return err
}
if _, err := c.Write(repData); err != nil {
return err
}
}
}