From 409a35189b23ca1490265c4eeb13ea370d3144ba Mon Sep 17 00:00:00 2001 From: Jianmin Date: Mon, 23 Dec 2024 17:47:26 +0800 Subject: [PATCH] [backport] ssh: implement strict KEX protocol changes --- vendor/golang.org/x/crypto/ssh/handshake.go | 59 +++++++++++++++++++-- vendor/golang.org/x/crypto/ssh/transport.go | 32 +++++++++-- 2 files changed, 81 insertions(+), 10 deletions(-) diff --git a/vendor/golang.org/x/crypto/ssh/handshake.go b/vendor/golang.org/x/crypto/ssh/handshake.go index 653dc4d..e7d4545 100644 --- a/vendor/golang.org/x/crypto/ssh/handshake.go +++ b/vendor/golang.org/x/crypto/ssh/handshake.go @@ -34,6 +34,16 @@ type keyingTransport interface { // direction will be effected if a msgNewKeys message is sent // or received. prepareKeyChange(*algorithms, *kexResult) error + + // setStrictMode sets the strict KEX mode, notably triggering + // sequence number resets on sending or receiving msgNewKeys. + // If the sequence number is already > 1 when setStrictMode + // is called, an error is returned. + setStrictMode() error + + // setInitialKEXDone indicates to the transport that the initial key exchange + // was completed + setInitialKEXDone() } // handshakeTransport implements rekeying on top of a keyingTransport @@ -94,6 +104,10 @@ type handshakeTransport struct { // The session ID or nil if first kex did not complete yet. sessionID []byte + + // strictMode indicates if the other side of the handshake indicated + // that we should be following the strict KEX protocol restrictions. + strictMode bool } type pendingKex struct { @@ -201,7 +215,10 @@ func (t *handshakeTransport) readLoop() { close(t.incoming) break } - if p[0] == msgIgnore || p[0] == msgDebug { + // If this is the first kex, and strict KEX mode is enabled, + // we don't ignore any messages, as they may be used to manipulate + // the packet sequence numbers. + if !(t.sessionID == nil && t.strictMode) && (p[0] == msgIgnore || p[0] == msgDebug) { continue } t.incoming <- p @@ -432,6 +449,11 @@ func (t *handshakeTransport) readOnePacket(first bool) ([]byte, error) { return successPacket, nil } +const ( + kexStrictClient = "kex-strict-c-v00@openssh.com" + kexStrictServer = "kex-strict-s-v00@openssh.com" +) + // sendKexInit sends a key change message. func (t *handshakeTransport) sendKexInit() error { t.mu.Lock() @@ -445,7 +467,6 @@ func (t *handshakeTransport) sendKexInit() error { } msg := &kexInitMsg{ - KexAlgos: t.config.KeyExchanges, CiphersClientServer: t.config.Ciphers, CiphersServerClient: t.config.Ciphers, MACsClientServer: t.config.MACs, @@ -455,6 +476,13 @@ func (t *handshakeTransport) sendKexInit() error { } io.ReadFull(rand.Reader, msg.Cookie[:]) + // We mutate the KexAlgos slice, in order to add the kex-strict extension algorithm, + // and possibly to add the ext-info extension algorithm. Since the slice may be the + // user owned KeyExchanges, we create our own slice in order to avoid using user + // owned memory by mistake. + msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+2) // room for kex-strict and ext-info + msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...) + isServer := len(t.hostKeys) > 0 if isServer { for _, k := range t.hostKeys { @@ -474,17 +502,24 @@ func (t *handshakeTransport) sendKexInit() error { msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, keyFormat) } } + + if t.sessionID == nil { + msg.KexAlgos = append(msg.KexAlgos, kexStrictServer) + } } else { msg.ServerHostKeyAlgos = t.hostKeyAlgorithms // As a client we opt in to receiving SSH_MSG_EXT_INFO so we know what // algorithms the server supports for public key authentication. See RFC // 8308, Section 2.1. + // + // We also send the strict KEX mode extension algorithm, in order to opt + // into the strict KEX mode. if firstKeyExchange := t.sessionID == nil; firstKeyExchange { - msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+1) - msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...) msg.KexAlgos = append(msg.KexAlgos, "ext-info-c") + msg.KexAlgos = append(msg.KexAlgos, kexStrictClient) } + } packet := Marshal(msg) @@ -581,6 +616,13 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error { return err } + if t.sessionID == nil && ((isClient && contains(serverInit.KexAlgos, kexStrictServer)) || (!isClient && contains(clientInit.KexAlgos, kexStrictClient))) { + t.strictMode = true + if err := t.conn.setStrictMode(); err != nil { + return err + } + } + // We don't send FirstKexFollows, but we handle receiving it. // // RFC 4253 section 7 defines the kex and the agreement method for @@ -615,7 +657,8 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error { return err } - if t.sessionID == nil { + firstKeyExchange := t.sessionID == nil + if firstKeyExchange { t.sessionID = result.H } result.SessionID = t.sessionID @@ -632,6 +675,12 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error { return unexpectedMessageError(msgNewKeys, packet[0]) } + if firstKeyExchange { + // Indicates to the transport that the first key exchange is completed + // after receiving SSH_MSG_NEWKEYS. + t.conn.setInitialKEXDone() + } + return nil } diff --git a/vendor/golang.org/x/crypto/ssh/transport.go b/vendor/golang.org/x/crypto/ssh/transport.go index acf5a21..4df45fc 100644 --- a/vendor/golang.org/x/crypto/ssh/transport.go +++ b/vendor/golang.org/x/crypto/ssh/transport.go @@ -48,6 +48,9 @@ type transport struct { rand io.Reader isClient bool io.Closer + + strictMode bool + initialKEXDone bool } // packetCipher represents a combination of SSH encryption/MAC @@ -73,6 +76,18 @@ type connectionState struct { pendingKeyChange chan packetCipher } +func (t *transport) setStrictMode() error { + if t.reader.seqNum != 1 { + return errors.New("ssh: sequence number != 1 when strict KEX mode requested") + } + t.strictMode = true + return nil +} + +func (t *transport) setInitialKEXDone() { + t.initialKEXDone = true +} + // prepareKeyChange sets up key material for a keychange. The key changes in // both directions are triggered by reading and writing a msgNewKey packet // respectively. @@ -111,11 +126,12 @@ func (t *transport) printPacket(p []byte, write bool) { // Read and decrypt next packet. func (t *transport) readPacket() (p []byte, err error) { for { - p, err = t.reader.readPacket(t.bufReader) + p, err = t.reader.readPacket(t.bufReader, t.strictMode) if err != nil { break } - if len(p) == 0 || (p[0] != msgIgnore && p[0] != msgDebug) { + // in strict mode we pass through DEBUG and IGNORE packets only during the initial KEX + if len(p) == 0 || (t.strictMode && !t.initialKEXDone) || (p[0] != msgIgnore && p[0] != msgDebug) { break } } @@ -126,7 +142,7 @@ func (t *transport) readPacket() (p []byte, err error) { return p, err } -func (s *connectionState) readPacket(r *bufio.Reader) ([]byte, error) { +func (s *connectionState) readPacket(r *bufio.Reader, strictMode bool) ([]byte, error) { packet, err := s.packetCipher.readCipherPacket(s.seqNum, r) s.seqNum++ if err == nil && len(packet) == 0 { @@ -139,6 +155,9 @@ func (s *connectionState) readPacket(r *bufio.Reader) ([]byte, error) { select { case cipher := <-s.pendingKeyChange: s.packetCipher = cipher + if strictMode { + s.seqNum = 0 + } default: return nil, errors.New("ssh: got bogus newkeys message") } @@ -169,10 +188,10 @@ func (t *transport) writePacket(packet []byte) error { if debugTransport { t.printPacket(packet, true) } - return t.writer.writePacket(t.bufWriter, t.rand, packet) + return t.writer.writePacket(t.bufWriter, t.rand, packet, t.strictMode) } -func (s *connectionState) writePacket(w *bufio.Writer, rand io.Reader, packet []byte) error { +func (s *connectionState) writePacket(w *bufio.Writer, rand io.Reader, packet []byte, strictMode bool) error { changeKeys := len(packet) > 0 && packet[0] == msgNewKeys err := s.packetCipher.writeCipherPacket(s.seqNum, w, rand, packet) @@ -187,6 +206,9 @@ func (s *connectionState) writePacket(w *bufio.Writer, rand io.Reader, packet [] select { case cipher := <-s.pendingKeyChange: s.packetCipher = cipher + if strictMode { + s.seqNum = 0 + } default: panic("ssh: no key material for msgNewKeys") } -- 2.39.5 (Apple Git-154)