// Copyright 2010 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. // TLS low level connection and record layer package tls import ( "bytes" "crypto/cipher" "crypto/subtle" "crypto/x509" "errors" "fmt" "io" "net" "sync" "sync/atomic" "time" ) // A Conn represents a secured connection. // It implements the net.Conn interface. type Conn struct { // constant conn net.Conn isClient bool // handshakeStatus is 1 if the connection is currently transferring // application data (i.e. is not currently processing a handshake). // This field is only to be accessed with sync/atomic. handshakeStatus uint32 // constant after handshake; protected by handshakeMutex handshakeMutex sync.Mutex handshakeErr error // error resulting from handshake vers uint16 // TLS version haveVers bool // version has been negotiated config *Config // configuration passed to constructor // handshakes counts the number of handshakes performed on the // connection so far. If renegotiation is disabled then this is either // zero or one. handshakes int didResume bool // whether this connection was a session resumption cipherSuite uint16 ocspResponse []byte // stapled OCSP response scts [][]byte // signed certificate timestamps from server peerCertificates []*x509.Certificate // verifiedChains contains the certificate chains that we built, as // opposed to the ones presented by the server. verifiedChains [][]*x509.Certificate // serverName contains the server name indicated by the client, if any. serverName string // secureRenegotiation is true if the server echoed the secure // renegotiation extension. (This is meaningless as a server because // renegotiation is not supported in that case.) secureRenegotiation bool // ekm is a closure for exporting keying material. ekm func(label string, context []byte, length int) ([]byte, error) // resumptionSecret is the resumption_master_secret for handling // NewSessionTicket messages. nil if config.SessionTicketsDisabled. resumptionSecret []byte // clientFinishedIsFirst is true if the client sent the first Finished // message during the most recent handshake. This is recorded because // the first transmitted Finished message is the tls-unique // channel-binding value. clientFinishedIsFirst bool // closeNotifyErr is any error from sending the alertCloseNotify record. closeNotifyErr error // closeNotifySent is true if the Conn attempted to send an // alertCloseNotify record. closeNotifySent bool // clientFinished and serverFinished contain the Finished message sent // by the client or server in the most recent handshake. This is // retained to support the renegotiation extension and tls-unique // channel-binding. clientFinished [12]byte serverFinished [12]byte clientProtocol string clientProtocolFallback bool // input/output in, out halfConn rawInput bytes.Buffer // raw input, starting with a record header input bytes.Reader // application data waiting to be read, from rawInput.Next hand bytes.Buffer // handshake data waiting to be read outBuf []byte // scratch buffer used by out.encrypt buffering bool // whether records are buffered in sendBuf sendBuf []byte // a buffer of records waiting to be sent // bytesSent counts the bytes of application data sent. // packetsSent counts packets. bytesSent int64 packetsSent int64 // retryCount counts the number of consecutive non-advancing records // received by Conn.readRecord. That is, records that neither advance the // handshake, nor deliver application data. Protected by in.Mutex. retryCount int // activeCall is an atomic int32; the low bit is whether Close has // been called. the rest of the bits are the number of goroutines // in Conn.Write. activeCall int32 tmp [16]byte } // Access to net.Conn methods. // Cannot just embed net.Conn because that would // export the struct field too. // LocalAddr returns the local network address. func (c *Conn) LocalAddr() net.Addr { return c.conn.LocalAddr() } // RemoteAddr returns the remote network address. func (c *Conn) RemoteAddr() net.Addr { return c.conn.RemoteAddr() } // SetDeadline sets the read and write deadlines associated with the connection. // A zero value for t means Read and Write will not time out. // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error. func (c *Conn) SetDeadline(t time.Time) error { return c.conn.SetDeadline(t) } // SetReadDeadline sets the read deadline on the underlying connection. // A zero value for t means Read will not time out. func (c *Conn) SetReadDeadline(t time.Time) error { return c.conn.SetReadDeadline(t) } // SetWriteDeadline sets the write deadline on the underlying connection. // A zero value for t means Write will not time out. // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error. func (c *Conn) SetWriteDeadline(t time.Time) error { return c.conn.SetWriteDeadline(t) } // A halfConn represents one direction of the record layer // connection, either sending or receiving. type halfConn struct { sync.Mutex err error // first permanent error version uint16 // protocol version cipher interface{} // cipher algorithm mac macFunction seq [8]byte // 64-bit sequence number additionalData [13]byte // to avoid allocs; interface method args escape nextCipher interface{} // next encryption state nextMac macFunction // next MAC algorithm trafficSecret []byte // current TLS 1.3 traffic secret } func (hc *halfConn) setErrorLocked(err error) error { hc.err = err return err } // prepareCipherSpec sets the encryption and MAC states // that a subsequent changeCipherSpec will use. func (hc *halfConn) prepareCipherSpec(version uint16, cipher interface{}, mac macFunction) { hc.version = version hc.nextCipher = cipher hc.nextMac = mac } // changeCipherSpec changes the encryption and MAC states // to the ones previously passed to prepareCipherSpec. func (hc *halfConn) changeCipherSpec() error { if hc.nextCipher == nil || hc.version == VersionTLS13 { return alertInternalError } hc.cipher = hc.nextCipher hc.mac = hc.nextMac hc.nextCipher = nil hc.nextMac = nil for i := range hc.seq { hc.seq[i] = 0 } return nil } func (hc *halfConn) setTrafficSecret(suite *cipherSuiteTLS13, secret []byte) { hc.trafficSecret = secret key, iv := suite.trafficKey(secret) hc.cipher = suite.aead(key, iv) for i := range hc.seq { hc.seq[i] = 0 } } // incSeq increments the sequence number. func (hc *halfConn) incSeq() { for i := 7; i >= 0; i-- { hc.seq[i]++ if hc.seq[i] != 0 { return } } // Not allowed to let sequence number wrap. // Instead, must renegotiate before it does. // Not likely enough to bother. panic("TLS: sequence number wraparound") } // explicitNonceLen returns the number of bytes of explicit nonce or IV included // in each record. Explicit nonces are present only in CBC modes after TLS 1.0 // and in certain AEAD modes in TLS 1.2. func (hc *halfConn) explicitNonceLen() int { if hc.cipher == nil { return 0 } switch c := hc.cipher.(type) { case cipher.Stream: return 0 case aead: return c.explicitNonceLen() case cbcMode: // TLS 1.1 introduced a per-record explicit IV to fix the BEAST attack. if hc.version >= VersionTLS11 { return c.BlockSize() } return 0 default: panic("unknown cipher type") } } // extractPadding returns, in constant time, the length of the padding to remove // from the end of payload. It also returns a byte which is equal to 255 if the // padding was valid and 0 otherwise. See RFC 2246, Section 6.2.3.2. func extractPadding(payload []byte) (toRemove int, good byte) { if len(payload) < 1 { return 0, 0 } paddingLen := payload[len(payload)-1] t := uint(len(payload)-1) - uint(paddingLen) // if len(payload) >= (paddingLen - 1) then the MSB of t is zero good = byte(int32(^t) >> 31) // The maximum possible padding length plus the actual length field toCheck := 256 // The length of the padded data is public, so we can use an if here if toCheck > len(payload) { toCheck = len(payload) } for i := 0; i < toCheck; i++ { t := uint(paddingLen) - uint(i) // if i <= paddingLen then the MSB of t is zero mask := byte(int32(^t) >> 31) b := payload[len(payload)-1-i] good &^= mask&paddingLen ^ mask&b } // We AND together the bits of good and replicate the result across // all the bits. good &= good << 4 good &= good << 2 good &= good << 1 good = uint8(int8(good) >> 7) toRemove = int(paddingLen) + 1 return } // extractPaddingSSL30 is a replacement for extractPadding in the case that the // protocol version is SSLv3. In this version, the contents of the padding // are random and cannot be checked. func extractPaddingSSL30(payload []byte) (toRemove int, good byte) { if len(payload) < 1 { return 0, 0 } paddingLen := int(payload[len(payload)-1]) + 1 if paddingLen > len(payload) { return 0, 0 } return paddingLen, 255 } func roundUp(a, b int) int { return a + (b-a%b)%b } // cbcMode is an interface for block ciphers using cipher block chaining. type cbcMode interface { cipher.BlockMode SetIV([]byte) } // decrypt authenticates and decrypts the record if protection is active at // this stage. The returned plaintext might overlap with the input. func (hc *halfConn) decrypt(record []byte) ([]byte, recordType, error) { var plaintext []byte typ := recordType(record[0]) payload := record[recordHeaderLen:] // In TLS 1.3, change_cipher_spec messages are to be ignored without being // decrypted. See RFC 8446, Appendix D.4. if hc.version == VersionTLS13 && typ == recordTypeChangeCipherSpec { return payload, typ, nil } paddingGood := byte(255) paddingLen := 0 explicitNonceLen := hc.explicitNonceLen() if hc.cipher != nil { switch c := hc.cipher.(type) { case cipher.Stream: c.XORKeyStream(payload, payload) case aead: if len(payload) < explicitNonceLen { return nil, 0, alertBadRecordMAC } nonce := payload[:explicitNonceLen] if len(nonce) == 0 { nonce = hc.seq[:] } payload = payload[explicitNonceLen:] additionalData := hc.additionalData[:] if hc.version == VersionTLS13 { additionalData = record[:recordHeaderLen] } else { copy(additionalData, hc.seq[:]) copy(additionalData[8:], record[:3]) n := len(payload) - c.Overhead() additionalData[11] = byte(n >> 8) additionalData[12] = byte(n) } var err error plaintext, err = c.Open(payload[:0], nonce, payload, additionalData) if err != nil { return nil, 0, alertBadRecordMAC } case cbcMode: blockSize := c.BlockSize() minPayload := explicitNonceLen + roundUp(hc.mac.Size()+1, blockSize) if len(payload)%blockSize != 0 || len(payload) < minPayload { return nil, 0, alertBadRecordMAC } if explicitNonceLen > 0 { c.SetIV(payload[:explicitNonceLen]) payload = payload[explicitNonceLen:] } c.CryptBlocks(payload, payload) // In a limited attempt to protect against CBC padding oracles like // Lucky13, the data past paddingLen (which is secret) is passed to // the MAC function as extra data, to be fed into the HMAC after // computing the digest. This makes the MAC roughly constant time as // long as the digest computation is constant time and does not // affect the subsequent write, modulo cache effects. if hc.version == VersionSSL30 { paddingLen, paddingGood = extractPaddingSSL30(payload) } else { paddingLen, paddingGood = extractPadding(payload) } default: panic("unknown cipher type") } if hc.version == VersionTLS13 { if typ != recordTypeApplicationData { return nil, 0, alertUnexpectedMessage } if len(plaintext) > maxPlaintext+1 { return nil, 0, alertRecordOverflow } // Remove padding and find the ContentType scanning from the end. for i := len(plaintext) - 1; i >= 0; i-- { if plaintext[i] != 0 { typ = recordType(plaintext[i]) plaintext = plaintext[:i] break } if i == 0 { return nil, 0, alertUnexpectedMessage } } } } else { plaintext = payload } if hc.mac != nil { macSize := hc.mac.Size() if len(payload) < macSize { return nil, 0, alertBadRecordMAC } n := len(payload) - macSize - paddingLen n = subtle.ConstantTimeSelect(int(uint32(n)>>31), 0, n) // if n < 0 { n = 0 } record[3] = byte(n >> 8) record[4] = byte(n) remoteMAC := payload[n : n+macSize] localMAC := hc.mac.MAC(hc.seq[0:], record[:recordHeaderLen], payload[:n], payload[n+macSize:]) if subtle.ConstantTimeCompare(localMAC, remoteMAC) != 1 || paddingGood != 255 { return nil, 0, alertBadRecordMAC } plaintext = payload[:n] } hc.incSeq() return plaintext, typ, nil } // sliceForAppend extends the input slice by n bytes. head is the full extended // slice, while tail is the appended part. If the original slice has sufficient // capacity no allocation is performed. func sliceForAppend(in []byte, n int) (head, tail []byte) { if total := len(in) + n; cap(in) >= total { head = in[:total] } else { head = make([]byte, total) copy(head, in) } tail = head[len(in):] return } // encrypt encrypts payload, adding the appropriate nonce and/or MAC, and // appends it to record, which contains the record header. func (hc *halfConn) encrypt(record, payload []byte, rand io.Reader) ([]byte, error) { if hc.cipher == nil { return append(record, payload...), nil } var explicitNonce []byte if explicitNonceLen := hc.explicitNonceLen(); explicitNonceLen > 0 { record, explicitNonce = sliceForAppend(record, explicitNonceLen) if _, isCBC := hc.cipher.(cbcMode); !isCBC && explicitNonceLen < 16 { // The AES-GCM construction in TLS has an explicit nonce so that the // nonce can be random. However, the nonce is only 8 bytes which is // too small for a secure, random nonce. Therefore we use the // sequence number as the nonce. The 3DES-CBC construction also has // an 8 bytes nonce but its nonces must be unpredictable (see RFC // 5246, Appendix F.3), forcing us to use randomness. That's not // 3DES' biggest problem anyway because the birthday bound on block // collision is reached first due to its simlarly small block size // (see the Sweet32 attack). copy(explicitNonce, hc.seq[:]) } else { if _, err := io.ReadFull(rand, explicitNonce); err != nil { return nil, err } } } var mac []byte if hc.mac != nil { mac = hc.mac.MAC(hc.seq[:], record[:recordHeaderLen], payload, nil) } var dst []byte switch c := hc.cipher.(type) { case cipher.Stream: record, dst = sliceForAppend(record, len(payload)+len(mac)) c.XORKeyStream(dst[:len(payload)], payload) c.XORKeyStream(dst[len(payload):], mac) case aead: nonce := explicitNonce if len(nonce) == 0 { nonce = hc.seq[:] } if hc.version == VersionTLS13 { record = append(record, payload...) // Encrypt the actual ContentType and replace the plaintext one. record = append(record, record[0]) record[0] = byte(recordTypeApplicationData) n := len(payload) + 1 + c.Overhead() record[3] = byte(n >> 8) record[4] = byte(n) record = c.Seal(record[:recordHeaderLen], nonce, record[recordHeaderLen:], record[:recordHeaderLen]) } else { copy(hc.additionalData[:], hc.seq[:]) copy(hc.additionalData[8:], record) record = c.Seal(record, nonce, payload, hc.additionalData[:]) } case cbcMode: blockSize := c.BlockSize() plaintextLen := len(payload) + len(mac) paddingLen := blockSize - plaintextLen%blockSize record, dst = sliceForAppend(record, plaintextLen+paddingLen) copy(dst, payload) copy(dst[len(payload):], mac) for i := plaintextLen; i < len(dst); i++ { dst[i] = byte(paddingLen - 1) } if len(explicitNonce) > 0 { c.SetIV(explicitNonce) } c.CryptBlocks(dst, dst) default: panic("unknown cipher type") } // Update length to include nonce, MAC and any block padding needed. n := len(record) - recordHeaderLen record[3] = byte(n >> 8) record[4] = byte(n) hc.incSeq() return record, nil } // RecordHeaderError is returned when a TLS record header is invalid. type RecordHeaderError struct { // Msg contains a human readable string that describes the error. Msg string // RecordHeader contains the five bytes of TLS record header that // triggered the error. RecordHeader [5]byte // Conn provides the underlying net.Conn in the case that a client // sent an initial handshake that didn't look like TLS. // It is nil if there's already been a handshake or a TLS alert has // been written to the connection. Conn net.Conn } func (e RecordHeaderError) Error() string { return "tls: " + e.Msg } func (c *Conn) newRecordHeaderError(conn net.Conn, msg string) (err RecordHeaderError) { err.Msg = msg err.Conn = conn copy(err.RecordHeader[:], c.rawInput.Bytes()) return err } func (c *Conn) readRecord() error { return c.readRecordOrCCS(false) } func (c *Conn) readChangeCipherSpec() error { return c.readRecordOrCCS(true) } // readRecordOrCCS reads one or more TLS records from the connection and // updates the record layer state. Some invariants: // * c.in must be locked // * c.input must be empty // During the handshake one and only one of the following will happen: // - c.hand grows // - c.in.changeCipherSpec is called // - an error is returned // After the handshake one and only one of the following will happen: // - c.hand grows // - c.input is set // - an error is returned func (c *Conn) readRecordOrCCS(expectChangeCipherSpec bool) error { if c.in.err != nil { return c.in.err } handshakeComplete := c.handshakeComplete() // This function modifies c.rawInput, which owns the c.input memory. if c.input.Len() != 0 { return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with pending application data")) } c.input.Reset(nil) // Read header, payload. if err := c.readFromUntil(c.conn, recordHeaderLen); err != nil { // RFC 8446, Section 6.1 suggests that EOF without an alertCloseNotify // is an error, but popular web sites seem to do this, so we accept it // if and only if at the record boundary. if err == io.ErrUnexpectedEOF && c.rawInput.Len() == 0 { err = io.EOF } if e, ok := err.(net.Error); !ok || !e.Temporary() { c.in.setErrorLocked(err) } return err } hdr := c.rawInput.Bytes()[:recordHeaderLen] typ := recordType(hdr[0]) // No valid TLS record has a type of 0x80, however SSLv2 handshakes // start with a uint16 length where the MSB is set and the first record // is always < 256 bytes long. Therefore typ == 0x80 strongly suggests // an SSLv2 client. if !handshakeComplete && typ == 0x80 { c.sendAlert(alertProtocolVersion) return c.in.setErrorLocked(c.newRecordHeaderError(nil, "unsupported SSLv2 handshake received")) } vers := uint16(hdr[1])<<8 | uint16(hdr[2]) n := int(hdr[3])<<8 | int(hdr[4]) if c.haveVers && c.vers != VersionTLS13 && vers != c.vers { c.sendAlert(alertProtocolVersion) msg := fmt.Sprintf("received record with version %x when expecting version %x", vers, c.vers) return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg)) } if !c.haveVers { // First message, be extra suspicious: this might not be a TLS // client. Bail out before reading a full 'body', if possible. // The current max version is 3.3 so if the version is >= 16.0, // it's probably not real. if (typ != recordTypeAlert && typ != recordTypeHandshake) || vers >= 0x1000 { return c.in.setErrorLocked(c.newRecordHeaderError(c.conn, "first record does not look like a TLS handshake")) } } if c.vers == VersionTLS13 && n > maxCiphertextTLS13 || n > maxCiphertext { c.sendAlert(alertRecordOverflow) msg := fmt.Sprintf("oversized record received with length %d", n) return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg)) } if err := c.readFromUntil(c.conn, recordHeaderLen+n); err != nil { if e, ok := err.(net.Error); !ok || !e.Temporary() { c.in.setErrorLocked(err) } return err } // Process message. record := c.rawInput.Next(recordHeaderLen + n) data, typ, err := c.in.decrypt(record) if err != nil { return c.in.setErrorLocked(c.sendAlert(err.(alert))) } if len(data) > maxPlaintext { return c.in.setErrorLocked(c.sendAlert(alertRecordOverflow)) } // Application Data messages are always protected. if c.in.cipher == nil && typ == recordTypeApplicationData { return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } if typ != recordTypeAlert && typ != recordTypeChangeCipherSpec && len(data) > 0 { // This is a state-advancing message: reset the retry count. c.retryCount = 0 } // Handshake messages MUST NOT be interleaved with other record types in TLS 1.3. if c.vers == VersionTLS13 && typ != recordTypeHandshake && c.hand.Len() > 0 { return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } switch typ { default: return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) case recordTypeAlert: if len(data) != 2 { return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } if alert(data[1]) == alertCloseNotify { return c.in.setErrorLocked(io.EOF) } if c.vers == VersionTLS13 { return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])}) } switch data[0] { case alertLevelWarning: // Drop the record on the floor and retry. return c.retryReadRecord(expectChangeCipherSpec) case alertLevelError: return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])}) default: return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } case recordTypeChangeCipherSpec: if len(data) != 1 || data[0] != 1 { return c.in.setErrorLocked(c.sendAlert(alertDecodeError)) } // Handshake messages are not allowed to fragment across the CCS. if c.hand.Len() > 0 { return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } // In TLS 1.3, change_cipher_spec records are ignored until the // Finished. See RFC 8446, Appendix D.4. Note that according to Section // 5, a server can send a ChangeCipherSpec before its ServerHello, when // c.vers is still unset. That's not useful though and suspicious if the // server then selects a lower protocol version, so don't allow that. if c.vers == VersionTLS13 { return c.retryReadRecord(expectChangeCipherSpec) } if !expectChangeCipherSpec { return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } if err := c.in.changeCipherSpec(); err != nil { return c.in.setErrorLocked(c.sendAlert(err.(alert))) } case recordTypeApplicationData: if !handshakeComplete || expectChangeCipherSpec { return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } // Some OpenSSL servers send empty records in order to randomize the // CBC IV. Ignore a limited number of empty records. if len(data) == 0 { return c.retryReadRecord(expectChangeCipherSpec) } // Note that data is owned by c.rawInput, following the Next call above, // to avoid copying the plaintext. This is safe because c.rawInput is // not read from or written to until c.input is drained. c.input.Reset(data) case recordTypeHandshake: if len(data) == 0 || expectChangeCipherSpec { return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } c.hand.Write(data) } return nil } // retryReadRecord recurses into readRecordOrCCS to drop a non-advancing record, like // a warning alert, empty application_data, or a change_cipher_spec in TLS 1.3. func (c *Conn) retryReadRecord(expectChangeCipherSpec bool) error { c.retryCount++ if c.retryCount > maxUselessRecords { c.sendAlert(alertUnexpectedMessage) return c.in.setErrorLocked(errors.New("tls: too many ignored records")) } return c.readRecordOrCCS(expectChangeCipherSpec) } // atLeastReader reads from R, stopping with EOF once at least N bytes have been // read. It is different from an io.LimitedReader in that it doesn't cut short // the last Read call, and in that it considers an early EOF an error. type atLeastReader struct { R io.Reader N int64 } func (r *atLeastReader) Read(p []byte) (int, error) { if r.N <= 0 { return 0, io.EOF } n, err := r.R.Read(p) r.N -= int64(n) // won't underflow unless len(p) >= n > 9223372036854775809 if r.N > 0 && err == io.EOF { return n, io.ErrUnexpectedEOF } if r.N <= 0 && err == nil { return n, io.EOF } return n, err } // readFromUntil reads from r into c.rawInput until c.rawInput contains // at least n bytes or else returns an error. func (c *Conn) readFromUntil(r io.Reader, n int) error { if c.rawInput.Len() >= n { return nil } needs := n - c.rawInput.Len() // There might be extra input waiting on the wire. Make a best effort // attempt to fetch it so that it can be used in (*Conn).Read to // "predict" closeNotify alerts. c.rawInput.Grow(needs + bytes.MinRead) _, err := c.rawInput.ReadFrom(&atLeastReader{r, int64(needs)}) return err } // sendAlert sends a TLS alert message. func (c *Conn) sendAlertLocked(err alert) error { switch err { case alertNoRenegotiation, alertCloseNotify: c.tmp[0] = alertLevelWarning default: c.tmp[0] = alertLevelError } c.tmp[1] = byte(err) _, writeErr := c.writeRecordLocked(recordTypeAlert, c.tmp[0:2]) if err == alertCloseNotify { // closeNotify is a special case in that it isn't an error. return writeErr } return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err}) } // sendAlert sends a TLS alert message. func (c *Conn) sendAlert(err alert) error { c.out.Lock() defer c.out.Unlock() return c.sendAlertLocked(err) } const ( // tcpMSSEstimate is a conservative estimate of the TCP maximum segment // size (MSS). A constant is used, rather than querying the kernel for // the actual MSS, to avoid complexity. The value here is the IPv6 // minimum MTU (1280 bytes) minus the overhead of an IPv6 header (40 // bytes) and a TCP header with timestamps (32 bytes). tcpMSSEstimate = 1208 // recordSizeBoostThreshold is the number of bytes of application data // sent after which the TLS record size will be increased to the // maximum. recordSizeBoostThreshold = 128 * 1024 ) // maxPayloadSizeForWrite returns the maximum TLS payload size to use for the // next application data record. There is the following trade-off: // // - For latency-sensitive applications, such as web browsing, each TLS // record should fit in one TCP segment. // - For throughput-sensitive applications, such as large file transfers, // larger TLS records better amortize framing and encryption overheads. // // A simple heuristic that works well in practice is to use small records for // the first 1MB of data, then use larger records for subsequent data, and // reset back to smaller records after the connection becomes idle. See "High // Performance Web Networking", Chapter 4, or: // https://www.igvita.com/2013/10/24/optimizing-tls-record-size-and-buffering-latency/ // // In the interests of simplicity and determinism, this code does not attempt // to reset the record size once the connection is idle, however. func (c *Conn) maxPayloadSizeForWrite(typ recordType) int { if c.config.DynamicRecordSizingDisabled || typ != recordTypeApplicationData { return maxPlaintext } if c.bytesSent >= recordSizeBoostThreshold { return maxPlaintext } // Subtract TLS overheads to get the maximum payload size. payloadBytes := tcpMSSEstimate - recordHeaderLen - c.out.explicitNonceLen() if c.out.cipher != nil { switch ciph := c.out.cipher.(type) { case cipher.Stream: payloadBytes -= c.out.mac.Size() case cipher.AEAD: payloadBytes -= ciph.Overhead() case cbcMode: blockSize := ciph.BlockSize() // The payload must fit in a multiple of blockSize, with // room for at least one padding byte. payloadBytes = (payloadBytes & ^(blockSize - 1)) - 1 // The MAC is appended before padding so affects the // payload size directly. payloadBytes -= c.out.mac.Size() default: panic("unknown cipher type") } } if c.vers == VersionTLS13 { payloadBytes-- // encrypted ContentType } // Allow packet growth in arithmetic progression up to max. pkt := c.packetsSent c.packetsSent++ if pkt > 1000 { return maxPlaintext // avoid overflow in multiply below } n := payloadBytes * int(pkt+1) if n > maxPlaintext { n = maxPlaintext } return n } func (c *Conn) write(data []byte) (int, error) { if c.buffering { c.sendBuf = append(c.sendBuf, data...) return len(data), nil } n, err := c.conn.Write(data) c.bytesSent += int64(n) return n, err } func (c *Conn) flush() (int, error) { if len(c.sendBuf) == 0 { return 0, nil } n, err := c.conn.Write(c.sendBuf) c.bytesSent += int64(n) c.sendBuf = nil c.buffering = false return n, err } // writeRecordLocked writes a TLS record with the given type and payload to the // connection and updates the record layer state. func (c *Conn) writeRecordLocked(typ recordType, data []byte) (int, error) { var n int for len(data) > 0 { m := len(data) if maxPayload := c.maxPayloadSizeForWrite(typ); m > maxPayload { m = maxPayload } _, c.outBuf = sliceForAppend(c.outBuf[:0], recordHeaderLen) c.outBuf[0] = byte(typ) vers := c.vers if vers == 0 { // Some TLS servers fail if the record version is // greater than TLS 1.0 for the initial ClientHello. vers = VersionTLS10 } else if vers == VersionTLS13 { // TLS 1.3 froze the record layer version to 1.2. // See RFC 8446, Section 5.1. vers = VersionTLS12 } c.outBuf[1] = byte(vers >> 8) c.outBuf[2] = byte(vers) c.outBuf[3] = byte(m >> 8) c.outBuf[4] = byte(m) var err error c.outBuf, err = c.out.encrypt(c.outBuf, data[:m], c.config.rand()) if err != nil { return n, err } if _, err := c.write(c.outBuf); err != nil { return n, err } n += m data = data[m:] } if typ == recordTypeChangeCipherSpec && c.vers != VersionTLS13 { if err := c.out.changeCipherSpec(); err != nil { return n, c.sendAlertLocked(err.(alert)) } } return n, nil } // writeRecord writes a TLS record with the given type and payload to the // connection and updates the record layer state. func (c *Conn) writeRecord(typ recordType, data []byte) (int, error) { c.out.Lock() defer c.out.Unlock() return c.writeRecordLocked(typ, data) } // readHandshake reads the next handshake message from // the record layer. func (c *Conn) readHandshake() (interface{}, error) { for c.hand.Len() < 4 { if err := c.readRecord(); err != nil { return nil, err } } data := c.hand.Bytes() n := int(data[1])<<16 | int(data[2])<<8 | int(data[3]) if n > maxHandshake { c.sendAlertLocked(alertInternalError) return nil, c.in.setErrorLocked(fmt.Errorf("tls: handshake message of length %d bytes exceeds maximum of %d bytes", n, maxHandshake)) } for c.hand.Len() < 4+n { if err := c.readRecord(); err != nil { return nil, err } } data = c.hand.Next(4 + n) var m handshakeMessage switch data[0] { case typeHelloRequest: m = new(helloRequestMsg) case typeClientHello: m = new(clientHelloMsg) case typeServerHello: m = new(serverHelloMsg) case typeNewSessionTicket: if c.vers == VersionTLS13 { m = new(newSessionTicketMsgTLS13) } else { m = new(newSessionTicketMsg) } case typeCertificate: if c.vers == VersionTLS13 { m = new(certificateMsgTLS13) } else { m = new(certificateMsg) } case typeCertificateRequest: if c.vers == VersionTLS13 { m = new(certificateRequestMsgTLS13) } else { m = &certificateRequestMsg{ hasSignatureAlgorithm: c.vers >= VersionTLS12, } } case typeCertificateStatus: m = new(certificateStatusMsg) case typeServerKeyExchange: m = new(serverKeyExchangeMsg) case typeServerHelloDone: m = new(serverHelloDoneMsg) case typeClientKeyExchange: m = new(clientKeyExchangeMsg) case typeCertificateVerify: m = &certificateVerifyMsg{ hasSignatureAlgorithm: c.vers >= VersionTLS12, } case typeNextProtocol: m = new(nextProtoMsg) case typeFinished: m = new(finishedMsg) case typeEncryptedExtensions: m = new(encryptedExtensionsMsg) case typeEndOfEarlyData: m = new(endOfEarlyDataMsg) case typeKeyUpdate: m = new(keyUpdateMsg) default: return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } // The handshake message unmarshalers // expect to be able to keep references to data, // so pass in a fresh copy that won't be overwritten. data = append([]byte(nil), data...) if !m.unmarshal(data) { return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage)) } return m, nil } var ( errClosed = errors.New("tls: use of closed connection") errShutdown = errors.New("tls: protocol is shutdown") ) // Write writes data to the connection. func (c *Conn) Write(b []byte) (int, error) { // interlock with Close below for { x := atomic.LoadInt32(&c.activeCall) if x&1 != 0 { return 0, errClosed } if atomic.CompareAndSwapInt32(&c.activeCall, x, x+2) { defer atomic.AddInt32(&c.activeCall, -2) break } } if err := c.Handshake(); err != nil { return 0, err } c.out.Lock() defer c.out.Unlock() if err := c.out.err; err != nil { return 0, err } if !c.handshakeComplete() { return 0, alertInternalError } if c.closeNotifySent { return 0, errShutdown } // SSL 3.0 and TLS 1.0 are susceptible to a chosen-plaintext // attack when using block mode ciphers due to predictable IVs. // This can be prevented by splitting each Application Data // record into two records, effectively randomizing the IV. // // https://www.openssl.org/~bodo/tls-cbc.txt // https://bugzilla.mozilla.org/show_bug.cgi?id=665814 // https://www.imperialviolet.org/2012/01/15/beastfollowup.html var m int if len(b) > 1 && c.vers <= VersionTLS10 { if _, ok := c.out.cipher.(cipher.BlockMode); ok { n, err := c.writeRecordLocked(recordTypeApplicationData, b[:1]) if err != nil { return n, c.out.setErrorLocked(err) } m, b = 1, b[1:] } } n, err := c.writeRecordLocked(recordTypeApplicationData, b) return n + m, c.out.setErrorLocked(err) } // handleRenegotiation processes a HelloRequest handshake message. func (c *Conn) handleRenegotiation() error { if c.vers == VersionTLS13 { return errors.New("tls: internal error: unexpected renegotiation") } msg, err := c.readHandshake() if err != nil { return err } helloReq, ok := msg.(*helloRequestMsg) if !ok { c.sendAlert(alertUnexpectedMessage) return unexpectedMessageError(helloReq, msg) } if !c.isClient { return c.sendAlert(alertNoRenegotiation) } switch c.config.Renegotiation { case RenegotiateNever: return c.sendAlert(alertNoRenegotiation) case RenegotiateOnceAsClient: if c.handshakes > 1 { return c.sendAlert(alertNoRenegotiation) } case RenegotiateFreelyAsClient: // Ok. default: c.sendAlert(alertInternalError) return errors.New("tls: unknown Renegotiation value") } c.handshakeMutex.Lock() defer c.handshakeMutex.Unlock() atomic.StoreUint32(&c.handshakeStatus, 0) if c.handshakeErr = c.clientHandshake(); c.handshakeErr == nil { c.handshakes++ } return c.handshakeErr } // handlePostHandshakeMessage processes a handshake message arrived after the // handshake is complete. Up to TLS 1.2, it indicates the start of a renegotiation. func (c *Conn) handlePostHandshakeMessage() error { if c.vers != VersionTLS13 { return c.handleRenegotiation() } msg, err := c.readHandshake() if err != nil { return err } c.retryCount++ if c.retryCount > maxUselessRecords { c.sendAlert(alertUnexpectedMessage) return c.in.setErrorLocked(errors.New("tls: too many non-advancing records")) } switch msg := msg.(type) { case *newSessionTicketMsgTLS13: return c.handleNewSessionTicket(msg) case *keyUpdateMsg: return c.handleKeyUpdate(msg) default: c.sendAlert(alertUnexpectedMessage) return fmt.Errorf("tls: received unexpected handshake message of type %T", msg) } } func (c *Conn) handleKeyUpdate(keyUpdate *keyUpdateMsg) error { cipherSuite := cipherSuiteTLS13ByID(c.cipherSuite) if cipherSuite == nil { return c.in.setErrorLocked(c.sendAlert(alertInternalError)) } newSecret := cipherSuite.nextTrafficSecret(c.in.trafficSecret) c.in.setTrafficSecret(cipherSuite, newSecret) if keyUpdate.updateRequested { c.out.Lock() defer c.out.Unlock() msg := &keyUpdateMsg{} _, err := c.writeRecordLocked(recordTypeHandshake, msg.marshal()) if err != nil { // Surface the error at the next write. c.out.setErrorLocked(err) return nil } newSecret := cipherSuite.nextTrafficSecret(c.out.trafficSecret) c.out.setTrafficSecret(cipherSuite, newSecret) } return nil } // Read can be made to time out and return a net.Error with Timeout() == true // after a fixed time limit; see SetDeadline and SetReadDeadline. func (c *Conn) Read(b []byte) (int, error) { if err := c.Handshake(); err != nil { return 0, err } if len(b) == 0 { // Put this after Handshake, in case people were calling // Read(nil) for the side effect of the Handshake. return 0, nil } c.in.Lock() defer c.in.Unlock() for c.input.Len() == 0 { if err := c.readRecord(); err != nil { return 0, err } for c.hand.Len() > 0 { if err := c.handlePostHandshakeMessage(); err != nil { return 0, err } } } n, _ := c.input.Read(b) // If a close-notify alert is waiting, read it so that we can return (n, // EOF) instead of (n, nil), to signal to the HTTP response reading // goroutine that the connection is now closed. This eliminates a race // where the HTTP response reading goroutine would otherwise not observe // the EOF until its next read, by which time a client goroutine might // have already tried to reuse the HTTP connection for a new request. // See https://golang.org/cl/76400046 and https://golang.org/issue/3514 if n != 0 && c.input.Len() == 0 && c.rawInput.Len() > 0 && recordType(c.rawInput.Bytes()[0]) == recordTypeAlert { if err := c.readRecord(); err != nil { return n, err // will be io.EOF on closeNotify } } return n, nil } // Close closes the connection. func (c *Conn) Close() error { // Interlock with Conn.Write above. var x int32 for { x = atomic.LoadInt32(&c.activeCall) if x&1 != 0 { return errClosed } if atomic.CompareAndSwapInt32(&c.activeCall, x, x|1) { break } } if x != 0 { // io.Writer and io.Closer should not be used concurrently. // If Close is called while a Write is currently in-flight, // interpret that as a sign that this Close is really just // being used to break the Write and/or clean up resources and // avoid sending the alertCloseNotify, which may block // waiting on handshakeMutex or the c.out mutex. return c.conn.Close() } var alertErr error if c.handshakeComplete() { alertErr = c.closeNotify() } if err := c.conn.Close(); err != nil { return err } return alertErr } var errEarlyCloseWrite = errors.New("tls: CloseWrite called before handshake complete") // CloseWrite shuts down the writing side of the connection. It should only be // called once the handshake has completed and does not call CloseWrite on the // underlying connection. Most callers should just use Close. func (c *Conn) CloseWrite() error { if !c.handshakeComplete() { return errEarlyCloseWrite } return c.closeNotify() } func (c *Conn) closeNotify() error { c.out.Lock() defer c.out.Unlock() if !c.closeNotifySent { c.closeNotifyErr = c.sendAlertLocked(alertCloseNotify) c.closeNotifySent = true } return c.closeNotifyErr } // Handshake runs the client or server handshake // protocol if it has not yet been run. // Most uses of this package need not call Handshake // explicitly: the first Read or Write will call it automatically. func (c *Conn) Handshake() error { c.handshakeMutex.Lock() defer c.handshakeMutex.Unlock() if err := c.handshakeErr; err != nil { return err } if c.handshakeComplete() { return nil } c.in.Lock() defer c.in.Unlock() if c.isClient { c.handshakeErr = c.clientHandshake() } else { c.handshakeErr = c.serverHandshake() } if c.handshakeErr == nil { c.handshakes++ } else { // If an error occurred during the hadshake try to flush the // alert that might be left in the buffer. c.flush() } if c.handshakeErr == nil && !c.handshakeComplete() { c.handshakeErr = errors.New("tls: internal error: handshake should have had a result") } return c.handshakeErr } // ConnectionState returns basic TLS details about the connection. func (c *Conn) ConnectionState() ConnectionState { c.handshakeMutex.Lock() defer c.handshakeMutex.Unlock() var state ConnectionState state.HandshakeComplete = c.handshakeComplete() state.ServerName = c.serverName if state.HandshakeComplete { state.Version = c.vers state.NegotiatedProtocol = c.clientProtocol state.DidResume = c.didResume state.NegotiatedProtocolIsMutual = !c.clientProtocolFallback state.CipherSuite = c.cipherSuite state.PeerCertificates = c.peerCertificates state.VerifiedChains = c.verifiedChains state.SignedCertificateTimestamps = c.scts state.OCSPResponse = c.ocspResponse if !c.didResume && c.vers != VersionTLS13 { if c.clientFinishedIsFirst { state.TLSUnique = c.clientFinished[:] } else { state.TLSUnique = c.serverFinished[:] } } if c.config.Renegotiation != RenegotiateNever { state.ekm = noExportedKeyingMaterial } else { state.ekm = c.ekm } } return state } // OCSPResponse returns the stapled OCSP response from the TLS server, if // any. (Only valid for client connections.) func (c *Conn) OCSPResponse() []byte { c.handshakeMutex.Lock() defer c.handshakeMutex.Unlock() return c.ocspResponse } // VerifyHostname checks that the peer certificate chain is valid for // connecting to host. If so, it returns nil; if not, it returns an error // describing the problem. func (c *Conn) VerifyHostname(host string) error { c.handshakeMutex.Lock() defer c.handshakeMutex.Unlock() if !c.isClient { return errors.New("tls: VerifyHostname called on TLS server connection") } if !c.handshakeComplete() { return errors.New("tls: handshake has not yet been performed") } if len(c.verifiedChains) == 0 { return errors.New("tls: handshake did not verify certificate chain") } return c.peerCertificates[0].VerifyHostname(host) } func (c *Conn) handshakeComplete() bool { return atomic.LoadUint32(&c.handshakeStatus) == 1 }