diff options
Diffstat (limited to 'vendor/golang.org/x/crypto/ssh/handshake.go')
| -rw-r--r-- | vendor/golang.org/x/crypto/ssh/handshake.go | 63 |
1 files changed, 59 insertions, 4 deletions
diff --git a/vendor/golang.org/x/crypto/ssh/handshake.go b/vendor/golang.org/x/crypto/ssh/handshake.go index 70a7369ff..56cdc7c21 100644 --- a/vendor/golang.org/x/crypto/ssh/handshake.go +++ b/vendor/golang.org/x/crypto/ssh/handshake.go @@ -11,6 +11,7 @@ import ( "io" "log" "net" + "strings" "sync" ) @@ -34,6 +35,16 @@ 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 @@ -50,6 +61,10 @@ type handshakeTransport struct { // connection. hostKeys []Signer + // publicKeyAuthAlgorithms is non-empty if we are the server. In that case, + // it contains the supported client public key authentication algorithms. + publicKeyAuthAlgorithms []string + // hostKeyAlgorithms is non-empty if we are the client. In that case, // we accept these key types from the server as host key. hostKeyAlgorithms []string @@ -95,6 +110,10 @@ 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 { @@ -141,6 +160,7 @@ func newClientTransport(conn keyingTransport, clientVersion, serverVersion []byt func newServerTransport(conn keyingTransport, clientVersion, serverVersion []byte, config *ServerConfig) *handshakeTransport { t := newHandshakeTransport(conn, &config.Config, clientVersion, serverVersion) t.hostKeys = config.hostKeys + t.publicKeyAuthAlgorithms = config.PublicKeyAuthAlgorithms go t.readLoop() go t.kexLoop() return t @@ -203,7 +223,10 @@ 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 @@ -435,6 +458,11 @@ 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() @@ -448,7 +476,6 @@ func (t *handshakeTransport) sendKexInit() error { } msg := &kexInitMsg{ - KexAlgos: t.config.KeyExchanges, CiphersClientServer: t.config.Ciphers, CiphersServerClient: t.config.Ciphers, MACsClientServer: t.config.MACs, @@ -458,6 +485,13 @@ 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 { @@ -482,17 +516,24 @@ 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) @@ -598,6 +639,13 @@ 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 @@ -649,6 +697,7 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error { // message with the server-sig-algs extension if the client supports it. See // RFC 8308, Sections 2.4 and 3.1, and [PROTOCOL], Section 1.9. if !isClient && firstKeyExchange && contains(clientInit.KexAlgos, "ext-info-c") { + supportedPubKeyAuthAlgosList := strings.Join(t.publicKeyAuthAlgorithms, ",") extInfo := &extInfoMsg{ NumExtensions: 2, Payload: make([]byte, 0, 4+15+4+len(supportedPubKeyAuthAlgosList)+4+16+4+1), @@ -672,6 +721,12 @@ 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 } |