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Source file src/crypto/tls/conn.go

Documentation: crypto/tls

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // TLS low level connection and record layer
     6  
     7  package tls
     8  
     9  import (
    10  	"bytes"
    11  	"context"
    12  	"crypto/cipher"
    13  	"crypto/subtle"
    14  	"crypto/x509"
    15  	"errors"
    16  	"fmt"
    17  	"hash"
    18  	"io"
    19  	"net"
    20  	"sync"
    21  	"sync/atomic"
    22  	"time"
    23  )
    24  
    25  // A Conn represents a secured connection.
    26  // It implements the net.Conn interface.
    27  type Conn struct {
    28  	// constant
    29  	conn        net.Conn
    30  	isClient    bool
    31  	handshakeFn func(context.Context) error // (*Conn).clientHandshake or serverHandshake
    32  
    33  	// handshakeStatus is 1 if the connection is currently transferring
    34  	// application data (i.e. is not currently processing a handshake).
    35  	// This field is only to be accessed with sync/atomic.
    36  	handshakeStatus uint32
    37  	// constant after handshake; protected by handshakeMutex
    38  	handshakeMutex sync.Mutex
    39  	handshakeErr   error   // error resulting from handshake
    40  	vers           uint16  // TLS version
    41  	haveVers       bool    // version has been negotiated
    42  	config         *Config // configuration passed to constructor
    43  	// handshakes counts the number of handshakes performed on the
    44  	// connection so far. If renegotiation is disabled then this is either
    45  	// zero or one.
    46  	handshakes       int
    47  	didResume        bool // whether this connection was a session resumption
    48  	cipherSuite      uint16
    49  	ocspResponse     []byte   // stapled OCSP response
    50  	scts             [][]byte // signed certificate timestamps from server
    51  	peerCertificates []*x509.Certificate
    52  	// verifiedChains contains the certificate chains that we built, as
    53  	// opposed to the ones presented by the server.
    54  	verifiedChains [][]*x509.Certificate
    55  	// serverName contains the server name indicated by the client, if any.
    56  	serverName string
    57  	// secureRenegotiation is true if the server echoed the secure
    58  	// renegotiation extension. (This is meaningless as a server because
    59  	// renegotiation is not supported in that case.)
    60  	secureRenegotiation bool
    61  	// ekm is a closure for exporting keying material.
    62  	ekm func(label string, context []byte, length int) ([]byte, error)
    63  	// resumptionSecret is the resumption_master_secret for handling
    64  	// NewSessionTicket messages. nil if config.SessionTicketsDisabled.
    65  	resumptionSecret []byte
    66  
    67  	// ticketKeys is the set of active session ticket keys for this
    68  	// connection. The first one is used to encrypt new tickets and
    69  	// all are tried to decrypt tickets.
    70  	ticketKeys []ticketKey
    71  
    72  	// clientFinishedIsFirst is true if the client sent the first Finished
    73  	// message during the most recent handshake. This is recorded because
    74  	// the first transmitted Finished message is the tls-unique
    75  	// channel-binding value.
    76  	clientFinishedIsFirst bool
    77  
    78  	// closeNotifyErr is any error from sending the alertCloseNotify record.
    79  	closeNotifyErr error
    80  	// closeNotifySent is true if the Conn attempted to send an
    81  	// alertCloseNotify record.
    82  	closeNotifySent bool
    83  
    84  	// clientFinished and serverFinished contain the Finished message sent
    85  	// by the client or server in the most recent handshake. This is
    86  	// retained to support the renegotiation extension and tls-unique
    87  	// channel-binding.
    88  	clientFinished [12]byte
    89  	serverFinished [12]byte
    90  
    91  	// clientProtocol is the negotiated ALPN protocol.
    92  	clientProtocol string
    93  
    94  	// input/output
    95  	in, out   halfConn
    96  	rawInput  bytes.Buffer // raw input, starting with a record header
    97  	input     bytes.Reader // application data waiting to be read, from rawInput.Next
    98  	hand      bytes.Buffer // handshake data waiting to be read
    99  	buffering bool         // whether records are buffered in sendBuf
   100  	sendBuf   []byte       // a buffer of records waiting to be sent
   101  
   102  	// bytesSent counts the bytes of application data sent.
   103  	// packetsSent counts packets.
   104  	bytesSent   int64
   105  	packetsSent int64
   106  
   107  	// retryCount counts the number of consecutive non-advancing records
   108  	// received by Conn.readRecord. That is, records that neither advance the
   109  	// handshake, nor deliver application data. Protected by in.Mutex.
   110  	retryCount int
   111  
   112  	// activeCall is an atomic int32; the low bit is whether Close has
   113  	// been called. the rest of the bits are the number of goroutines
   114  	// in Conn.Write.
   115  	activeCall int32
   116  
   117  	tmp [16]byte
   118  }
   119  
   120  // Access to net.Conn methods.
   121  // Cannot just embed net.Conn because that would
   122  // export the struct field too.
   123  
   124  // LocalAddr returns the local network address.
   125  func (c *Conn) LocalAddr() net.Addr {
   126  	return c.conn.LocalAddr()
   127  }
   128  
   129  // RemoteAddr returns the remote network address.
   130  func (c *Conn) RemoteAddr() net.Addr {
   131  	return c.conn.RemoteAddr()
   132  }
   133  
   134  // SetDeadline sets the read and write deadlines associated with the connection.
   135  // A zero value for t means Read and Write will not time out.
   136  // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
   137  func (c *Conn) SetDeadline(t time.Time) error {
   138  	return c.conn.SetDeadline(t)
   139  }
   140  
   141  // SetReadDeadline sets the read deadline on the underlying connection.
   142  // A zero value for t means Read will not time out.
   143  func (c *Conn) SetReadDeadline(t time.Time) error {
   144  	return c.conn.SetReadDeadline(t)
   145  }
   146  
   147  // SetWriteDeadline sets the write deadline on the underlying connection.
   148  // A zero value for t means Write will not time out.
   149  // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
   150  func (c *Conn) SetWriteDeadline(t time.Time) error {
   151  	return c.conn.SetWriteDeadline(t)
   152  }
   153  
   154  // A halfConn represents one direction of the record layer
   155  // connection, either sending or receiving.
   156  type halfConn struct {
   157  	sync.Mutex
   158  
   159  	err     error       // first permanent error
   160  	version uint16      // protocol version
   161  	cipher  interface{} // cipher algorithm
   162  	mac     hash.Hash
   163  	seq     [8]byte // 64-bit sequence number
   164  
   165  	scratchBuf [13]byte // to avoid allocs; interface method args escape
   166  
   167  	nextCipher interface{} // next encryption state
   168  	nextMac    hash.Hash   // next MAC algorithm
   169  
   170  	trafficSecret []byte // current TLS 1.3 traffic secret
   171  }
   172  
   173  type permanentError struct {
   174  	err net.Error
   175  }
   176  
   177  func (e *permanentError) Error() string   { return e.err.Error() }
   178  func (e *permanentError) Unwrap() error   { return e.err }
   179  func (e *permanentError) Timeout() bool   { return e.err.Timeout() }
   180  func (e *permanentError) Temporary() bool { return false }
   181  
   182  func (hc *halfConn) setErrorLocked(err error) error {
   183  	if e, ok := err.(net.Error); ok {
   184  		hc.err = &permanentError{err: e}
   185  	} else {
   186  		hc.err = err
   187  	}
   188  	return hc.err
   189  }
   190  
   191  // prepareCipherSpec sets the encryption and MAC states
   192  // that a subsequent changeCipherSpec will use.
   193  func (hc *halfConn) prepareCipherSpec(version uint16, cipher interface{}, mac hash.Hash) {
   194  	hc.version = version
   195  	hc.nextCipher = cipher
   196  	hc.nextMac = mac
   197  }
   198  
   199  // changeCipherSpec changes the encryption and MAC states
   200  // to the ones previously passed to prepareCipherSpec.
   201  func (hc *halfConn) changeCipherSpec() error {
   202  	if hc.nextCipher == nil || hc.version == VersionTLS13 {
   203  		return alertInternalError
   204  	}
   205  	hc.cipher = hc.nextCipher
   206  	hc.mac = hc.nextMac
   207  	hc.nextCipher = nil
   208  	hc.nextMac = nil
   209  	for i := range hc.seq {
   210  		hc.seq[i] = 0
   211  	}
   212  	return nil
   213  }
   214  
   215  func (hc *halfConn) setTrafficSecret(suite *cipherSuiteTLS13, secret []byte) {
   216  	hc.trafficSecret = secret
   217  	key, iv := suite.trafficKey(secret)
   218  	hc.cipher = suite.aead(key, iv)
   219  	for i := range hc.seq {
   220  		hc.seq[i] = 0
   221  	}
   222  }
   223  
   224  // incSeq increments the sequence number.
   225  func (hc *halfConn) incSeq() {
   226  	for i := 7; i >= 0; i-- {
   227  		hc.seq[i]++
   228  		if hc.seq[i] != 0 {
   229  			return
   230  		}
   231  	}
   232  
   233  	// Not allowed to let sequence number wrap.
   234  	// Instead, must renegotiate before it does.
   235  	// Not likely enough to bother.
   236  	panic("TLS: sequence number wraparound")
   237  }
   238  
   239  // explicitNonceLen returns the number of bytes of explicit nonce or IV included
   240  // in each record. Explicit nonces are present only in CBC modes after TLS 1.0
   241  // and in certain AEAD modes in TLS 1.2.
   242  func (hc *halfConn) explicitNonceLen() int {
   243  	if hc.cipher == nil {
   244  		return 0
   245  	}
   246  
   247  	switch c := hc.cipher.(type) {
   248  	case cipher.Stream:
   249  		return 0
   250  	case aead:
   251  		return c.explicitNonceLen()
   252  	case cbcMode:
   253  		// TLS 1.1 introduced a per-record explicit IV to fix the BEAST attack.
   254  		if hc.version >= VersionTLS11 {
   255  			return c.BlockSize()
   256  		}
   257  		return 0
   258  	default:
   259  		panic("unknown cipher type")
   260  	}
   261  }
   262  
   263  // extractPadding returns, in constant time, the length of the padding to remove
   264  // from the end of payload. It also returns a byte which is equal to 255 if the
   265  // padding was valid and 0 otherwise. See RFC 2246, Section 6.2.3.2.
   266  func extractPadding(payload []byte) (toRemove int, good byte) {
   267  	if len(payload) < 1 {
   268  		return 0, 0
   269  	}
   270  
   271  	paddingLen := payload[len(payload)-1]
   272  	t := uint(len(payload)-1) - uint(paddingLen)
   273  	// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
   274  	good = byte(int32(^t) >> 31)
   275  
   276  	// The maximum possible padding length plus the actual length field
   277  	toCheck := 256
   278  	// The length of the padded data is public, so we can use an if here
   279  	if toCheck > len(payload) {
   280  		toCheck = len(payload)
   281  	}
   282  
   283  	for i := 0; i < toCheck; i++ {
   284  		t := uint(paddingLen) - uint(i)
   285  		// if i <= paddingLen then the MSB of t is zero
   286  		mask := byte(int32(^t) >> 31)
   287  		b := payload[len(payload)-1-i]
   288  		good &^= mask&paddingLen ^ mask&b
   289  	}
   290  
   291  	// We AND together the bits of good and replicate the result across
   292  	// all the bits.
   293  	good &= good << 4
   294  	good &= good << 2
   295  	good &= good << 1
   296  	good = uint8(int8(good) >> 7)
   297  
   298  	// Zero the padding length on error. This ensures any unchecked bytes
   299  	// are included in the MAC. Otherwise, an attacker that could
   300  	// distinguish MAC failures from padding failures could mount an attack
   301  	// similar to POODLE in SSL 3.0: given a good ciphertext that uses a
   302  	// full block's worth of padding, replace the final block with another
   303  	// block. If the MAC check passed but the padding check failed, the
   304  	// last byte of that block decrypted to the block size.
   305  	//
   306  	// See also macAndPaddingGood logic below.
   307  	paddingLen &= good
   308  
   309  	toRemove = int(paddingLen) + 1
   310  	return
   311  }
   312  
   313  func roundUp(a, b int) int {
   314  	return a + (b-a%b)%b
   315  }
   316  
   317  // cbcMode is an interface for block ciphers using cipher block chaining.
   318  type cbcMode interface {
   319  	cipher.BlockMode
   320  	SetIV([]byte)
   321  }
   322  
   323  // decrypt authenticates and decrypts the record if protection is active at
   324  // this stage. The returned plaintext might overlap with the input.
   325  func (hc *halfConn) decrypt(record []byte) ([]byte, recordType, error) {
   326  	var plaintext []byte
   327  	typ := recordType(record[0])
   328  	payload := record[recordHeaderLen:]
   329  
   330  	// In TLS 1.3, change_cipher_spec messages are to be ignored without being
   331  	// decrypted. See RFC 8446, Appendix D.4.
   332  	if hc.version == VersionTLS13 && typ == recordTypeChangeCipherSpec {
   333  		return payload, typ, nil
   334  	}
   335  
   336  	paddingGood := byte(255)
   337  	paddingLen := 0
   338  
   339  	explicitNonceLen := hc.explicitNonceLen()
   340  
   341  	if hc.cipher != nil {
   342  		switch c := hc.cipher.(type) {
   343  		case cipher.Stream:
   344  			c.XORKeyStream(payload, payload)
   345  		case aead:
   346  			if len(payload) < explicitNonceLen {
   347  				return nil, 0, alertBadRecordMAC
   348  			}
   349  			nonce := payload[:explicitNonceLen]
   350  			if len(nonce) == 0 {
   351  				nonce = hc.seq[:]
   352  			}
   353  			payload = payload[explicitNonceLen:]
   354  
   355  			var additionalData []byte
   356  			if hc.version == VersionTLS13 {
   357  				additionalData = record[:recordHeaderLen]
   358  			} else {
   359  				additionalData = append(hc.scratchBuf[:0], hc.seq[:]...)
   360  				additionalData = append(additionalData, record[:3]...)
   361  				n := len(payload) - c.Overhead()
   362  				additionalData = append(additionalData, byte(n>>8), byte(n))
   363  			}
   364  
   365  			var err error
   366  			plaintext, err = c.Open(payload[:0], nonce, payload, additionalData)
   367  			if err != nil {
   368  				return nil, 0, alertBadRecordMAC
   369  			}
   370  		case cbcMode:
   371  			blockSize := c.BlockSize()
   372  			minPayload := explicitNonceLen + roundUp(hc.mac.Size()+1, blockSize)
   373  			if len(payload)%blockSize != 0 || len(payload) < minPayload {
   374  				return nil, 0, alertBadRecordMAC
   375  			}
   376  
   377  			if explicitNonceLen > 0 {
   378  				c.SetIV(payload[:explicitNonceLen])
   379  				payload = payload[explicitNonceLen:]
   380  			}
   381  			c.CryptBlocks(payload, payload)
   382  
   383  			// In a limited attempt to protect against CBC padding oracles like
   384  			// Lucky13, the data past paddingLen (which is secret) is passed to
   385  			// the MAC function as extra data, to be fed into the HMAC after
   386  			// computing the digest. This makes the MAC roughly constant time as
   387  			// long as the digest computation is constant time and does not
   388  			// affect the subsequent write, modulo cache effects.
   389  			paddingLen, paddingGood = extractPadding(payload)
   390  		default:
   391  			panic("unknown cipher type")
   392  		}
   393  
   394  		if hc.version == VersionTLS13 {
   395  			if typ != recordTypeApplicationData {
   396  				return nil, 0, alertUnexpectedMessage
   397  			}
   398  			if len(plaintext) > maxPlaintext+1 {
   399  				return nil, 0, alertRecordOverflow
   400  			}
   401  			// Remove padding and find the ContentType scanning from the end.
   402  			for i := len(plaintext) - 1; i >= 0; i-- {
   403  				if plaintext[i] != 0 {
   404  					typ = recordType(plaintext[i])
   405  					plaintext = plaintext[:i]
   406  					break
   407  				}
   408  				if i == 0 {
   409  					return nil, 0, alertUnexpectedMessage
   410  				}
   411  			}
   412  		}
   413  	} else {
   414  		plaintext = payload
   415  	}
   416  
   417  	if hc.mac != nil {
   418  		macSize := hc.mac.Size()
   419  		if len(payload) < macSize {
   420  			return nil, 0, alertBadRecordMAC
   421  		}
   422  
   423  		n := len(payload) - macSize - paddingLen
   424  		n = subtle.ConstantTimeSelect(int(uint32(n)>>31), 0, n) // if n < 0 { n = 0 }
   425  		record[3] = byte(n >> 8)
   426  		record[4] = byte(n)
   427  		remoteMAC := payload[n : n+macSize]
   428  		localMAC := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload[:n], payload[n+macSize:])
   429  
   430  		// This is equivalent to checking the MACs and paddingGood
   431  		// separately, but in constant-time to prevent distinguishing
   432  		// padding failures from MAC failures. Depending on what value
   433  		// of paddingLen was returned on bad padding, distinguishing
   434  		// bad MAC from bad padding can lead to an attack.
   435  		//
   436  		// See also the logic at the end of extractPadding.
   437  		macAndPaddingGood := subtle.ConstantTimeCompare(localMAC, remoteMAC) & int(paddingGood)
   438  		if macAndPaddingGood != 1 {
   439  			return nil, 0, alertBadRecordMAC
   440  		}
   441  
   442  		plaintext = payload[:n]
   443  	}
   444  
   445  	hc.incSeq()
   446  	return plaintext, typ, nil
   447  }
   448  
   449  // sliceForAppend extends the input slice by n bytes. head is the full extended
   450  // slice, while tail is the appended part. If the original slice has sufficient
   451  // capacity no allocation is performed.
   452  func sliceForAppend(in []byte, n int) (head, tail []byte) {
   453  	if total := len(in) + n; cap(in) >= total {
   454  		head = in[:total]
   455  	} else {
   456  		head = make([]byte, total)
   457  		copy(head, in)
   458  	}
   459  	tail = head[len(in):]
   460  	return
   461  }
   462  
   463  // encrypt encrypts payload, adding the appropriate nonce and/or MAC, and
   464  // appends it to record, which must already contain the record header.
   465  func (hc *halfConn) encrypt(record, payload []byte, rand io.Reader) ([]byte, error) {
   466  	if hc.cipher == nil {
   467  		return append(record, payload...), nil
   468  	}
   469  
   470  	var explicitNonce []byte
   471  	if explicitNonceLen := hc.explicitNonceLen(); explicitNonceLen > 0 {
   472  		record, explicitNonce = sliceForAppend(record, explicitNonceLen)
   473  		if _, isCBC := hc.cipher.(cbcMode); !isCBC && explicitNonceLen < 16 {
   474  			// The AES-GCM construction in TLS has an explicit nonce so that the
   475  			// nonce can be random. However, the nonce is only 8 bytes which is
   476  			// too small for a secure, random nonce. Therefore we use the
   477  			// sequence number as the nonce. The 3DES-CBC construction also has
   478  			// an 8 bytes nonce but its nonces must be unpredictable (see RFC
   479  			// 5246, Appendix F.3), forcing us to use randomness. That's not
   480  			// 3DES' biggest problem anyway because the birthday bound on block
   481  			// collision is reached first due to its similarly small block size
   482  			// (see the Sweet32 attack).
   483  			copy(explicitNonce, hc.seq[:])
   484  		} else {
   485  			if _, err := io.ReadFull(rand, explicitNonce); err != nil {
   486  				return nil, err
   487  			}
   488  		}
   489  	}
   490  
   491  	var dst []byte
   492  	switch c := hc.cipher.(type) {
   493  	case cipher.Stream:
   494  		mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
   495  		record, dst = sliceForAppend(record, len(payload)+len(mac))
   496  		c.XORKeyStream(dst[:len(payload)], payload)
   497  		c.XORKeyStream(dst[len(payload):], mac)
   498  	case aead:
   499  		nonce := explicitNonce
   500  		if len(nonce) == 0 {
   501  			nonce = hc.seq[:]
   502  		}
   503  
   504  		if hc.version == VersionTLS13 {
   505  			record = append(record, payload...)
   506  
   507  			// Encrypt the actual ContentType and replace the plaintext one.
   508  			record = append(record, record[0])
   509  			record[0] = byte(recordTypeApplicationData)
   510  
   511  			n := len(payload) + 1 + c.Overhead()
   512  			record[3] = byte(n >> 8)
   513  			record[4] = byte(n)
   514  
   515  			record = c.Seal(record[:recordHeaderLen],
   516  				nonce, record[recordHeaderLen:], record[:recordHeaderLen])
   517  		} else {
   518  			additionalData := append(hc.scratchBuf[:0], hc.seq[:]...)
   519  			additionalData = append(additionalData, record[:recordHeaderLen]...)
   520  			record = c.Seal(record, nonce, payload, additionalData)
   521  		}
   522  	case cbcMode:
   523  		mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
   524  		blockSize := c.BlockSize()
   525  		plaintextLen := len(payload) + len(mac)
   526  		paddingLen := blockSize - plaintextLen%blockSize
   527  		record, dst = sliceForAppend(record, plaintextLen+paddingLen)
   528  		copy(dst, payload)
   529  		copy(dst[len(payload):], mac)
   530  		for i := plaintextLen; i < len(dst); i++ {
   531  			dst[i] = byte(paddingLen - 1)
   532  		}
   533  		if len(explicitNonce) > 0 {
   534  			c.SetIV(explicitNonce)
   535  		}
   536  		c.CryptBlocks(dst, dst)
   537  	default:
   538  		panic("unknown cipher type")
   539  	}
   540  
   541  	// Update length to include nonce, MAC and any block padding needed.
   542  	n := len(record) - recordHeaderLen
   543  	record[3] = byte(n >> 8)
   544  	record[4] = byte(n)
   545  	hc.incSeq()
   546  
   547  	return record, nil
   548  }
   549  
   550  // RecordHeaderError is returned when a TLS record header is invalid.
   551  type RecordHeaderError struct {
   552  	// Msg contains a human readable string that describes the error.
   553  	Msg string
   554  	// RecordHeader contains the five bytes of TLS record header that
   555  	// triggered the error.
   556  	RecordHeader [5]byte
   557  	// Conn provides the underlying net.Conn in the case that a client
   558  	// sent an initial handshake that didn't look like TLS.
   559  	// It is nil if there's already been a handshake or a TLS alert has
   560  	// been written to the connection.
   561  	Conn net.Conn
   562  }
   563  
   564  func (e RecordHeaderError) Error() string { return "tls: " + e.Msg }
   565  
   566  func (c *Conn) newRecordHeaderError(conn net.Conn, msg string) (err RecordHeaderError) {
   567  	err.Msg = msg
   568  	err.Conn = conn
   569  	copy(err.RecordHeader[:], c.rawInput.Bytes())
   570  	return err
   571  }
   572  
   573  func (c *Conn) readRecord() error {
   574  	return c.readRecordOrCCS(false)
   575  }
   576  
   577  func (c *Conn) readChangeCipherSpec() error {
   578  	return c.readRecordOrCCS(true)
   579  }
   580  
   581  // readRecordOrCCS reads one or more TLS records from the connection and
   582  // updates the record layer state. Some invariants:
   583  //   * c.in must be locked
   584  //   * c.input must be empty
   585  // During the handshake one and only one of the following will happen:
   586  //   - c.hand grows
   587  //   - c.in.changeCipherSpec is called
   588  //   - an error is returned
   589  // After the handshake one and only one of the following will happen:
   590  //   - c.hand grows
   591  //   - c.input is set
   592  //   - an error is returned
   593  func (c *Conn) readRecordOrCCS(expectChangeCipherSpec bool) error {
   594  	if c.in.err != nil {
   595  		return c.in.err
   596  	}
   597  	handshakeComplete := c.handshakeComplete()
   598  
   599  	// This function modifies c.rawInput, which owns the c.input memory.
   600  	if c.input.Len() != 0 {
   601  		return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with pending application data"))
   602  	}
   603  	c.input.Reset(nil)
   604  
   605  	// Read header, payload.
   606  	if err := c.readFromUntil(c.conn, recordHeaderLen); err != nil {
   607  		// RFC 8446, Section 6.1 suggests that EOF without an alertCloseNotify
   608  		// is an error, but popular web sites seem to do this, so we accept it
   609  		// if and only if at the record boundary.
   610  		if err == io.ErrUnexpectedEOF && c.rawInput.Len() == 0 {
   611  			err = io.EOF
   612  		}
   613  		if e, ok := err.(net.Error); !ok || !e.Temporary() {
   614  			c.in.setErrorLocked(err)
   615  		}
   616  		return err
   617  	}
   618  	hdr := c.rawInput.Bytes()[:recordHeaderLen]
   619  	typ := recordType(hdr[0])
   620  
   621  	// No valid TLS record has a type of 0x80, however SSLv2 handshakes
   622  	// start with a uint16 length where the MSB is set and the first record
   623  	// is always < 256 bytes long. Therefore typ == 0x80 strongly suggests
   624  	// an SSLv2 client.
   625  	if !handshakeComplete && typ == 0x80 {
   626  		c.sendAlert(alertProtocolVersion)
   627  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, "unsupported SSLv2 handshake received"))
   628  	}
   629  
   630  	vers := uint16(hdr[1])<<8 | uint16(hdr[2])
   631  	n := int(hdr[3])<<8 | int(hdr[4])
   632  	if c.haveVers && c.vers != VersionTLS13 && vers != c.vers {
   633  		c.sendAlert(alertProtocolVersion)
   634  		msg := fmt.Sprintf("received record with version %x when expecting version %x", vers, c.vers)
   635  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
   636  	}
   637  	if !c.haveVers {
   638  		// First message, be extra suspicious: this might not be a TLS
   639  		// client. Bail out before reading a full 'body', if possible.
   640  		// The current max version is 3.3 so if the version is >= 16.0,
   641  		// it's probably not real.
   642  		if (typ != recordTypeAlert && typ != recordTypeHandshake) || vers >= 0x1000 {
   643  			return c.in.setErrorLocked(c.newRecordHeaderError(c.conn, "first record does not look like a TLS handshake"))
   644  		}
   645  	}
   646  	if c.vers == VersionTLS13 && n > maxCiphertextTLS13 || n > maxCiphertext {
   647  		c.sendAlert(alertRecordOverflow)
   648  		msg := fmt.Sprintf("oversized record received with length %d", n)
   649  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
   650  	}
   651  	if err := c.readFromUntil(c.conn, recordHeaderLen+n); err != nil {
   652  		if e, ok := err.(net.Error); !ok || !e.Temporary() {
   653  			c.in.setErrorLocked(err)
   654  		}
   655  		return err
   656  	}
   657  
   658  	// Process message.
   659  	record := c.rawInput.Next(recordHeaderLen + n)
   660  	data, typ, err := c.in.decrypt(record)
   661  	if err != nil {
   662  		return c.in.setErrorLocked(c.sendAlert(err.(alert)))
   663  	}
   664  	if len(data) > maxPlaintext {
   665  		return c.in.setErrorLocked(c.sendAlert(alertRecordOverflow))
   666  	}
   667  
   668  	// Application Data messages are always protected.
   669  	if c.in.cipher == nil && typ == recordTypeApplicationData {
   670  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   671  	}
   672  
   673  	if typ != recordTypeAlert && typ != recordTypeChangeCipherSpec && len(data) > 0 {
   674  		// This is a state-advancing message: reset the retry count.
   675  		c.retryCount = 0
   676  	}
   677  
   678  	// Handshake messages MUST NOT be interleaved with other record types in TLS 1.3.
   679  	if c.vers == VersionTLS13 && typ != recordTypeHandshake && c.hand.Len() > 0 {
   680  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   681  	}
   682  
   683  	switch typ {
   684  	default:
   685  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   686  
   687  	case recordTypeAlert:
   688  		if len(data) != 2 {
   689  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   690  		}
   691  		if alert(data[1]) == alertCloseNotify {
   692  			return c.in.setErrorLocked(io.EOF)
   693  		}
   694  		if c.vers == VersionTLS13 {
   695  			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   696  		}
   697  		switch data[0] {
   698  		case alertLevelWarning:
   699  			// Drop the record on the floor and retry.
   700  			return c.retryReadRecord(expectChangeCipherSpec)
   701  		case alertLevelError:
   702  			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   703  		default:
   704  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   705  		}
   706  
   707  	case recordTypeChangeCipherSpec:
   708  		if len(data) != 1 || data[0] != 1 {
   709  			return c.in.setErrorLocked(c.sendAlert(alertDecodeError))
   710  		}
   711  		// Handshake messages are not allowed to fragment across the CCS.
   712  		if c.hand.Len() > 0 {
   713  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   714  		}
   715  		// In TLS 1.3, change_cipher_spec records are ignored until the
   716  		// Finished. See RFC 8446, Appendix D.4. Note that according to Section
   717  		// 5, a server can send a ChangeCipherSpec before its ServerHello, when
   718  		// c.vers is still unset. That's not useful though and suspicious if the
   719  		// server then selects a lower protocol version, so don't allow that.
   720  		if c.vers == VersionTLS13 {
   721  			return c.retryReadRecord(expectChangeCipherSpec)
   722  		}
   723  		if !expectChangeCipherSpec {
   724  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   725  		}
   726  		if err := c.in.changeCipherSpec(); err != nil {
   727  			return c.in.setErrorLocked(c.sendAlert(err.(alert)))
   728  		}
   729  
   730  	case recordTypeApplicationData:
   731  		if !handshakeComplete || expectChangeCipherSpec {
   732  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   733  		}
   734  		// Some OpenSSL servers send empty records in order to randomize the
   735  		// CBC IV. Ignore a limited number of empty records.
   736  		if len(data) == 0 {
   737  			return c.retryReadRecord(expectChangeCipherSpec)
   738  		}
   739  		// Note that data is owned by c.rawInput, following the Next call above,
   740  		// to avoid copying the plaintext. This is safe because c.rawInput is
   741  		// not read from or written to until c.input is drained.
   742  		c.input.Reset(data)
   743  
   744  	case recordTypeHandshake:
   745  		if len(data) == 0 || expectChangeCipherSpec {
   746  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   747  		}
   748  		c.hand.Write(data)
   749  	}
   750  
   751  	return nil
   752  }
   753  
   754  // retryReadRecord recurses into readRecordOrCCS to drop a non-advancing record, like
   755  // a warning alert, empty application_data, or a change_cipher_spec in TLS 1.3.
   756  func (c *Conn) retryReadRecord(expectChangeCipherSpec bool) error {
   757  	c.retryCount++
   758  	if c.retryCount > maxUselessRecords {
   759  		c.sendAlert(alertUnexpectedMessage)
   760  		return c.in.setErrorLocked(errors.New("tls: too many ignored records"))
   761  	}
   762  	return c.readRecordOrCCS(expectChangeCipherSpec)
   763  }
   764  
   765  // atLeastReader reads from R, stopping with EOF once at least N bytes have been
   766  // read. It is different from an io.LimitedReader in that it doesn't cut short
   767  // the last Read call, and in that it considers an early EOF an error.
   768  type atLeastReader struct {
   769  	R io.Reader
   770  	N int64
   771  }
   772  
   773  func (r *atLeastReader) Read(p []byte) (int, error) {
   774  	if r.N <= 0 {
   775  		return 0, io.EOF
   776  	}
   777  	n, err := r.R.Read(p)
   778  	r.N -= int64(n) // won't underflow unless len(p) >= n > 9223372036854775809
   779  	if r.N > 0 && err == io.EOF {
   780  		return n, io.ErrUnexpectedEOF
   781  	}
   782  	if r.N <= 0 && err == nil {
   783  		return n, io.EOF
   784  	}
   785  	return n, err
   786  }
   787  
   788  // readFromUntil reads from r into c.rawInput until c.rawInput contains
   789  // at least n bytes or else returns an error.
   790  func (c *Conn) readFromUntil(r io.Reader, n int) error {
   791  	if c.rawInput.Len() >= n {
   792  		return nil
   793  	}
   794  	needs := n - c.rawInput.Len()
   795  	// There might be extra input waiting on the wire. Make a best effort
   796  	// attempt to fetch it so that it can be used in (*Conn).Read to
   797  	// "predict" closeNotify alerts.
   798  	c.rawInput.Grow(needs + bytes.MinRead)
   799  	_, err := c.rawInput.ReadFrom(&atLeastReader{r, int64(needs)})
   800  	return err
   801  }
   802  
   803  // sendAlert sends a TLS alert message.
   804  func (c *Conn) sendAlertLocked(err alert) error {
   805  	switch err {
   806  	case alertNoRenegotiation, alertCloseNotify:
   807  		c.tmp[0] = alertLevelWarning
   808  	default:
   809  		c.tmp[0] = alertLevelError
   810  	}
   811  	c.tmp[1] = byte(err)
   812  
   813  	_, writeErr := c.writeRecordLocked(recordTypeAlert, c.tmp[0:2])
   814  	if err == alertCloseNotify {
   815  		// closeNotify is a special case in that it isn't an error.
   816  		return writeErr
   817  	}
   818  
   819  	return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
   820  }
   821  
   822  // sendAlert sends a TLS alert message.
   823  func (c *Conn) sendAlert(err alert) error {
   824  	c.out.Lock()
   825  	defer c.out.Unlock()
   826  	return c.sendAlertLocked(err)
   827  }
   828  
   829  const (
   830  	// tcpMSSEstimate is a conservative estimate of the TCP maximum segment
   831  	// size (MSS). A constant is used, rather than querying the kernel for
   832  	// the actual MSS, to avoid complexity. The value here is the IPv6
   833  	// minimum MTU (1280 bytes) minus the overhead of an IPv6 header (40
   834  	// bytes) and a TCP header with timestamps (32 bytes).
   835  	tcpMSSEstimate = 1208
   836  
   837  	// recordSizeBoostThreshold is the number of bytes of application data
   838  	// sent after which the TLS record size will be increased to the
   839  	// maximum.
   840  	recordSizeBoostThreshold = 128 * 1024
   841  )
   842  
   843  // maxPayloadSizeForWrite returns the maximum TLS payload size to use for the
   844  // next application data record. There is the following trade-off:
   845  //
   846  //   - For latency-sensitive applications, such as web browsing, each TLS
   847  //     record should fit in one TCP segment.
   848  //   - For throughput-sensitive applications, such as large file transfers,
   849  //     larger TLS records better amortize framing and encryption overheads.
   850  //
   851  // A simple heuristic that works well in practice is to use small records for
   852  // the first 1MB of data, then use larger records for subsequent data, and
   853  // reset back to smaller records after the connection becomes idle. See "High
   854  // Performance Web Networking", Chapter 4, or:
   855  // https://www.igvita.com/2013/10/24/optimizing-tls-record-size-and-buffering-latency/
   856  //
   857  // In the interests of simplicity and determinism, this code does not attempt
   858  // to reset the record size once the connection is idle, however.
   859  func (c *Conn) maxPayloadSizeForWrite(typ recordType) int {
   860  	if c.config.DynamicRecordSizingDisabled || typ != recordTypeApplicationData {
   861  		return maxPlaintext
   862  	}
   863  
   864  	if c.bytesSent >= recordSizeBoostThreshold {
   865  		return maxPlaintext
   866  	}
   867  
   868  	// Subtract TLS overheads to get the maximum payload size.
   869  	payloadBytes := tcpMSSEstimate - recordHeaderLen - c.out.explicitNonceLen()
   870  	if c.out.cipher != nil {
   871  		switch ciph := c.out.cipher.(type) {
   872  		case cipher.Stream:
   873  			payloadBytes -= c.out.mac.Size()
   874  		case cipher.AEAD:
   875  			payloadBytes -= ciph.Overhead()
   876  		case cbcMode:
   877  			blockSize := ciph.BlockSize()
   878  			// The payload must fit in a multiple of blockSize, with
   879  			// room for at least one padding byte.
   880  			payloadBytes = (payloadBytes & ^(blockSize - 1)) - 1
   881  			// The MAC is appended before padding so affects the
   882  			// payload size directly.
   883  			payloadBytes -= c.out.mac.Size()
   884  		default:
   885  			panic("unknown cipher type")
   886  		}
   887  	}
   888  	if c.vers == VersionTLS13 {
   889  		payloadBytes-- // encrypted ContentType
   890  	}
   891  
   892  	// Allow packet growth in arithmetic progression up to max.
   893  	pkt := c.packetsSent
   894  	c.packetsSent++
   895  	if pkt > 1000 {
   896  		return maxPlaintext // avoid overflow in multiply below
   897  	}
   898  
   899  	n := payloadBytes * int(pkt+1)
   900  	if n > maxPlaintext {
   901  		n = maxPlaintext
   902  	}
   903  	return n
   904  }
   905  
   906  func (c *Conn) write(data []byte) (int, error) {
   907  	if c.buffering {
   908  		c.sendBuf = append(c.sendBuf, data...)
   909  		return len(data), nil
   910  	}
   911  
   912  	n, err := c.conn.Write(data)
   913  	c.bytesSent += int64(n)
   914  	return n, err
   915  }
   916  
   917  func (c *Conn) flush() (int, error) {
   918  	if len(c.sendBuf) == 0 {
   919  		return 0, nil
   920  	}
   921  
   922  	n, err := c.conn.Write(c.sendBuf)
   923  	c.bytesSent += int64(n)
   924  	c.sendBuf = nil
   925  	c.buffering = false
   926  	return n, err
   927  }
   928  
   929  // outBufPool pools the record-sized scratch buffers used by writeRecordLocked.
   930  var outBufPool = sync.Pool{
   931  	New: func() interface{} {
   932  		return new([]byte)
   933  	},
   934  }
   935  
   936  // writeRecordLocked writes a TLS record with the given type and payload to the
   937  // connection and updates the record layer state.
   938  func (c *Conn) writeRecordLocked(typ recordType, data []byte) (int, error) {
   939  	outBufPtr := outBufPool.Get().(*[]byte)
   940  	outBuf := *outBufPtr
   941  	defer func() {
   942  		// You might be tempted to simplify this by just passing &outBuf to Put,
   943  		// but that would make the local copy of the outBuf slice header escape
   944  		// to the heap, causing an allocation. Instead, we keep around the
   945  		// pointer to the slice header returned by Get, which is already on the
   946  		// heap, and overwrite and return that.
   947  		*outBufPtr = outBuf
   948  		outBufPool.Put(outBufPtr)
   949  	}()
   950  
   951  	var n int
   952  	for len(data) > 0 {
   953  		m := len(data)
   954  		if maxPayload := c.maxPayloadSizeForWrite(typ); m > maxPayload {
   955  			m = maxPayload
   956  		}
   957  
   958  		_, outBuf = sliceForAppend(outBuf[:0], recordHeaderLen)
   959  		outBuf[0] = byte(typ)
   960  		vers := c.vers
   961  		if vers == 0 {
   962  			// Some TLS servers fail if the record version is
   963  			// greater than TLS 1.0 for the initial ClientHello.
   964  			vers = VersionTLS10
   965  		} else if vers == VersionTLS13 {
   966  			// TLS 1.3 froze the record layer version to 1.2.
   967  			// See RFC 8446, Section 5.1.
   968  			vers = VersionTLS12
   969  		}
   970  		outBuf[1] = byte(vers >> 8)
   971  		outBuf[2] = byte(vers)
   972  		outBuf[3] = byte(m >> 8)
   973  		outBuf[4] = byte(m)
   974  
   975  		var err error
   976  		outBuf, err = c.out.encrypt(outBuf, data[:m], c.config.rand())
   977  		if err != nil {
   978  			return n, err
   979  		}
   980  		if _, err := c.write(outBuf); err != nil {
   981  			return n, err
   982  		}
   983  		n += m
   984  		data = data[m:]
   985  	}
   986  
   987  	if typ == recordTypeChangeCipherSpec && c.vers != VersionTLS13 {
   988  		if err := c.out.changeCipherSpec(); err != nil {
   989  			return n, c.sendAlertLocked(err.(alert))
   990  		}
   991  	}
   992  
   993  	return n, nil
   994  }
   995  
   996  // writeRecord writes a TLS record with the given type and payload to the
   997  // connection and updates the record layer state.
   998  func (c *Conn) writeRecord(typ recordType, data []byte) (int, error) {
   999  	c.out.Lock()
  1000  	defer c.out.Unlock()
  1001  
  1002  	return c.writeRecordLocked(typ, data)
  1003  }
  1004  
  1005  // readHandshake reads the next handshake message from
  1006  // the record layer.
  1007  func (c *Conn) readHandshake() (interface{}, error) {
  1008  	for c.hand.Len() < 4 {
  1009  		if err := c.readRecord(); err != nil {
  1010  			return nil, err
  1011  		}
  1012  	}
  1013  
  1014  	data := c.hand.Bytes()
  1015  	n := int(data[1])<<16 | int(data[2])<<8 | int(data[3])
  1016  	if n > maxHandshake {
  1017  		c.sendAlertLocked(alertInternalError)
  1018  		return nil, c.in.setErrorLocked(fmt.Errorf("tls: handshake message of length %d bytes exceeds maximum of %d bytes", n, maxHandshake))
  1019  	}
  1020  	for c.hand.Len() < 4+n {
  1021  		if err := c.readRecord(); err != nil {
  1022  			return nil, err
  1023  		}
  1024  	}
  1025  	data = c.hand.Next(4 + n)
  1026  	var m handshakeMessage
  1027  	switch data[0] {
  1028  	case typeHelloRequest:
  1029  		m = new(helloRequestMsg)
  1030  	case typeClientHello:
  1031  		m = new(clientHelloMsg)
  1032  	case typeServerHello:
  1033  		m = new(serverHelloMsg)
  1034  	case typeNewSessionTicket:
  1035  		if c.vers == VersionTLS13 {
  1036  			m = new(newSessionTicketMsgTLS13)
  1037  		} else {
  1038  			m = new(newSessionTicketMsg)
  1039  		}
  1040  	case typeCertificate:
  1041  		if c.vers == VersionTLS13 {
  1042  			m = new(certificateMsgTLS13)
  1043  		} else {
  1044  			m = new(certificateMsg)
  1045  		}
  1046  	case typeCertificateRequest:
  1047  		if c.vers == VersionTLS13 {
  1048  			m = new(certificateRequestMsgTLS13)
  1049  		} else {
  1050  			m = &certificateRequestMsg{
  1051  				hasSignatureAlgorithm: c.vers >= VersionTLS12,
  1052  			}
  1053  		}
  1054  	case typeCertificateStatus:
  1055  		m = new(certificateStatusMsg)
  1056  	case typeServerKeyExchange:
  1057  		m = new(serverKeyExchangeMsg)
  1058  	case typeServerHelloDone:
  1059  		m = new(serverHelloDoneMsg)
  1060  	case typeClientKeyExchange:
  1061  		m = new(clientKeyExchangeMsg)
  1062  	case typeCertificateVerify:
  1063  		m = &certificateVerifyMsg{
  1064  			hasSignatureAlgorithm: c.vers >= VersionTLS12,
  1065  		}
  1066  	case typeFinished:
  1067  		m = new(finishedMsg)
  1068  	case typeEncryptedExtensions:
  1069  		m = new(encryptedExtensionsMsg)
  1070  	case typeEndOfEarlyData:
  1071  		m = new(endOfEarlyDataMsg)
  1072  	case typeKeyUpdate:
  1073  		m = new(keyUpdateMsg)
  1074  	default:
  1075  		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
  1076  	}
  1077  
  1078  	// The handshake message unmarshalers
  1079  	// expect to be able to keep references to data,
  1080  	// so pass in a fresh copy that won't be overwritten.
  1081  	data = append([]byte(nil), data...)
  1082  
  1083  	if !m.unmarshal(data) {
  1084  		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
  1085  	}
  1086  	return m, nil
  1087  }
  1088  
  1089  var (
  1090  	errShutdown = errors.New("tls: protocol is shutdown")
  1091  )
  1092  
  1093  // Write writes data to the connection.
  1094  //
  1095  // As Write calls Handshake, in order to prevent indefinite blocking a deadline
  1096  // must be set for both Read and Write before Write is called when the handshake
  1097  // has not yet completed. See SetDeadline, SetReadDeadline, and
  1098  // SetWriteDeadline.
  1099  func (c *Conn) Write(b []byte) (int, error) {
  1100  	// interlock with Close below
  1101  	for {
  1102  		x := atomic.LoadInt32(&c.activeCall)
  1103  		if x&1 != 0 {
  1104  			return 0, net.ErrClosed
  1105  		}
  1106  		if atomic.CompareAndSwapInt32(&c.activeCall, x, x+2) {
  1107  			break
  1108  		}
  1109  	}
  1110  	defer atomic.AddInt32(&c.activeCall, -2)
  1111  
  1112  	if err := c.Handshake(); err != nil {
  1113  		return 0, err
  1114  	}
  1115  
  1116  	c.out.Lock()
  1117  	defer c.out.Unlock()
  1118  
  1119  	if err := c.out.err; err != nil {
  1120  		return 0, err
  1121  	}
  1122  
  1123  	if !c.handshakeComplete() {
  1124  		return 0, alertInternalError
  1125  	}
  1126  
  1127  	if c.closeNotifySent {
  1128  		return 0, errShutdown
  1129  	}
  1130  
  1131  	// TLS 1.0 is susceptible to a chosen-plaintext
  1132  	// attack when using block mode ciphers due to predictable IVs.
  1133  	// This can be prevented by splitting each Application Data
  1134  	// record into two records, effectively randomizing the IV.
  1135  	//
  1136  	// https://www.openssl.org/~bodo/tls-cbc.txt
  1137  	// https://bugzilla.mozilla.org/show_bug.cgi?id=665814
  1138  	// https://www.imperialviolet.org/2012/01/15/beastfollowup.html
  1139  
  1140  	var m int
  1141  	if len(b) > 1 && c.vers == VersionTLS10 {
  1142  		if _, ok := c.out.cipher.(cipher.BlockMode); ok {
  1143  			n, err := c.writeRecordLocked(recordTypeApplicationData, b[:1])
  1144  			if err != nil {
  1145  				return n, c.out.setErrorLocked(err)
  1146  			}
  1147  			m, b = 1, b[1:]
  1148  		}
  1149  	}
  1150  
  1151  	n, err := c.writeRecordLocked(recordTypeApplicationData, b)
  1152  	return n + m, c.out.setErrorLocked(err)
  1153  }
  1154  
  1155  // handleRenegotiation processes a HelloRequest handshake message.
  1156  func (c *Conn) handleRenegotiation() error {
  1157  	if c.vers == VersionTLS13 {
  1158  		return errors.New("tls: internal error: unexpected renegotiation")
  1159  	}
  1160  
  1161  	msg, err := c.readHandshake()
  1162  	if err != nil {
  1163  		return err
  1164  	}
  1165  
  1166  	helloReq, ok := msg.(*helloRequestMsg)
  1167  	if !ok {
  1168  		c.sendAlert(alertUnexpectedMessage)
  1169  		return unexpectedMessageError(helloReq, msg)
  1170  	}
  1171  
  1172  	if !c.isClient {
  1173  		return c.sendAlert(alertNoRenegotiation)
  1174  	}
  1175  
  1176  	switch c.config.Renegotiation {
  1177  	case RenegotiateNever:
  1178  		return c.sendAlert(alertNoRenegotiation)
  1179  	case RenegotiateOnceAsClient:
  1180  		if c.handshakes > 1 {
  1181  			return c.sendAlert(alertNoRenegotiation)
  1182  		}
  1183  	case RenegotiateFreelyAsClient:
  1184  		// Ok.
  1185  	default:
  1186  		c.sendAlert(alertInternalError)
  1187  		return errors.New("tls: unknown Renegotiation value")
  1188  	}
  1189  
  1190  	c.handshakeMutex.Lock()
  1191  	defer c.handshakeMutex.Unlock()
  1192  
  1193  	atomic.StoreUint32(&c.handshakeStatus, 0)
  1194  	if c.handshakeErr = c.clientHandshake(context.Background()); c.handshakeErr == nil {
  1195  		c.handshakes++
  1196  	}
  1197  	return c.handshakeErr
  1198  }
  1199  
  1200  // handlePostHandshakeMessage processes a handshake message arrived after the
  1201  // handshake is complete. Up to TLS 1.2, it indicates the start of a renegotiation.
  1202  func (c *Conn) handlePostHandshakeMessage() error {
  1203  	if c.vers != VersionTLS13 {
  1204  		return c.handleRenegotiation()
  1205  	}
  1206  
  1207  	msg, err := c.readHandshake()
  1208  	if err != nil {
  1209  		return err
  1210  	}
  1211  
  1212  	c.retryCount++
  1213  	if c.retryCount > maxUselessRecords {
  1214  		c.sendAlert(alertUnexpectedMessage)
  1215  		return c.in.setErrorLocked(errors.New("tls: too many non-advancing records"))
  1216  	}
  1217  
  1218  	switch msg := msg.(type) {
  1219  	case *newSessionTicketMsgTLS13:
  1220  		return c.handleNewSessionTicket(msg)
  1221  	case *keyUpdateMsg:
  1222  		return c.handleKeyUpdate(msg)
  1223  	default:
  1224  		c.sendAlert(alertUnexpectedMessage)
  1225  		return fmt.Errorf("tls: received unexpected handshake message of type %T", msg)
  1226  	}
  1227  }
  1228  
  1229  func (c *Conn) handleKeyUpdate(keyUpdate *keyUpdateMsg) error {
  1230  	cipherSuite := cipherSuiteTLS13ByID(c.cipherSuite)
  1231  	if cipherSuite == nil {
  1232  		return c.in.setErrorLocked(c.sendAlert(alertInternalError))
  1233  	}
  1234  
  1235  	newSecret := cipherSuite.nextTrafficSecret(c.in.trafficSecret)
  1236  	c.in.setTrafficSecret(cipherSuite, newSecret)
  1237  
  1238  	if keyUpdate.updateRequested {
  1239  		c.out.Lock()
  1240  		defer c.out.Unlock()
  1241  
  1242  		msg := &keyUpdateMsg{}
  1243  		_, err := c.writeRecordLocked(recordTypeHandshake, msg.marshal())
  1244  		if err != nil {
  1245  			// Surface the error at the next write.
  1246  			c.out.setErrorLocked(err)
  1247  			return nil
  1248  		}
  1249  
  1250  		newSecret := cipherSuite.nextTrafficSecret(c.out.trafficSecret)
  1251  		c.out.setTrafficSecret(cipherSuite, newSecret)
  1252  	}
  1253  
  1254  	return nil
  1255  }
  1256  
  1257  // Read reads data from the connection.
  1258  //
  1259  // As Read calls Handshake, in order to prevent indefinite blocking a deadline
  1260  // must be set for both Read and Write before Read is called when the handshake
  1261  // has not yet completed. See SetDeadline, SetReadDeadline, and
  1262  // SetWriteDeadline.
  1263  func (c *Conn) Read(b []byte) (int, error) {
  1264  	if err := c.Handshake(); err != nil {
  1265  		return 0, err
  1266  	}
  1267  	if len(b) == 0 {
  1268  		// Put this after Handshake, in case people were calling
  1269  		// Read(nil) for the side effect of the Handshake.
  1270  		return 0, nil
  1271  	}
  1272  
  1273  	c.in.Lock()
  1274  	defer c.in.Unlock()
  1275  
  1276  	for c.input.Len() == 0 {
  1277  		if err := c.readRecord(); err != nil {
  1278  			return 0, err
  1279  		}
  1280  		for c.hand.Len() > 0 {
  1281  			if err := c.handlePostHandshakeMessage(); err != nil {
  1282  				return 0, err
  1283  			}
  1284  		}
  1285  	}
  1286  
  1287  	n, _ := c.input.Read(b)
  1288  
  1289  	// If a close-notify alert is waiting, read it so that we can return (n,
  1290  	// EOF) instead of (n, nil), to signal to the HTTP response reading
  1291  	// goroutine that the connection is now closed. This eliminates a race
  1292  	// where the HTTP response reading goroutine would otherwise not observe
  1293  	// the EOF until its next read, by which time a client goroutine might
  1294  	// have already tried to reuse the HTTP connection for a new request.
  1295  	// See https://golang.org/cl/76400046 and https://golang.org/issue/3514
  1296  	if n != 0 && c.input.Len() == 0 && c.rawInput.Len() > 0 &&
  1297  		recordType(c.rawInput.Bytes()[0]) == recordTypeAlert {
  1298  		if err := c.readRecord(); err != nil {
  1299  			return n, err // will be io.EOF on closeNotify
  1300  		}
  1301  	}
  1302  
  1303  	return n, nil
  1304  }
  1305  
  1306  // Close closes the connection.
  1307  func (c *Conn) Close() error {
  1308  	// Interlock with Conn.Write above.
  1309  	var x int32
  1310  	for {
  1311  		x = atomic.LoadInt32(&c.activeCall)
  1312  		if x&1 != 0 {
  1313  			return net.ErrClosed
  1314  		}
  1315  		if atomic.CompareAndSwapInt32(&c.activeCall, x, x|1) {
  1316  			break
  1317  		}
  1318  	}
  1319  	if x != 0 {
  1320  		// io.Writer and io.Closer should not be used concurrently.
  1321  		// If Close is called while a Write is currently in-flight,
  1322  		// interpret that as a sign that this Close is really just
  1323  		// being used to break the Write and/or clean up resources and
  1324  		// avoid sending the alertCloseNotify, which may block
  1325  		// waiting on handshakeMutex or the c.out mutex.
  1326  		return c.conn.Close()
  1327  	}
  1328  
  1329  	var alertErr error
  1330  	if c.handshakeComplete() {
  1331  		if err := c.closeNotify(); err != nil {
  1332  			alertErr = fmt.Errorf("tls: failed to send closeNotify alert (but connection was closed anyway): %w", err)
  1333  		}
  1334  	}
  1335  
  1336  	if err := c.conn.Close(); err != nil {
  1337  		return err
  1338  	}
  1339  	return alertErr
  1340  }
  1341  
  1342  var errEarlyCloseWrite = errors.New("tls: CloseWrite called before handshake complete")
  1343  
  1344  // CloseWrite shuts down the writing side of the connection. It should only be
  1345  // called once the handshake has completed and does not call CloseWrite on the
  1346  // underlying connection. Most callers should just use Close.
  1347  func (c *Conn) CloseWrite() error {
  1348  	if !c.handshakeComplete() {
  1349  		return errEarlyCloseWrite
  1350  	}
  1351  
  1352  	return c.closeNotify()
  1353  }
  1354  
  1355  func (c *Conn) closeNotify() error {
  1356  	c.out.Lock()
  1357  	defer c.out.Unlock()
  1358  
  1359  	if !c.closeNotifySent {
  1360  		// Set a Write Deadline to prevent possibly blocking forever.
  1361  		c.SetWriteDeadline(time.Now().Add(time.Second * 5))
  1362  		c.closeNotifyErr = c.sendAlertLocked(alertCloseNotify)
  1363  		c.closeNotifySent = true
  1364  		// Any subsequent writes will fail.
  1365  		c.SetWriteDeadline(time.Now())
  1366  	}
  1367  	return c.closeNotifyErr
  1368  }
  1369  
  1370  // Handshake runs the client or server handshake
  1371  // protocol if it has not yet been run.
  1372  //
  1373  // Most uses of this package need not call Handshake explicitly: the
  1374  // first Read or Write will call it automatically.
  1375  //
  1376  // For control over canceling or setting a timeout on a handshake, use
  1377  // HandshakeContext or the Dialer's DialContext method instead.
  1378  func (c *Conn) Handshake() error {
  1379  	return c.HandshakeContext(context.Background())
  1380  }
  1381  
  1382  // HandshakeContext runs the client or server handshake
  1383  // protocol if it has not yet been run.
  1384  //
  1385  // The provided Context must be non-nil. If the context is canceled before
  1386  // the handshake is complete, the handshake is interrupted and an error is returned.
  1387  // Once the handshake has completed, cancellation of the context will not affect the
  1388  // connection.
  1389  //
  1390  // Most uses of this package need not call HandshakeContext explicitly: the
  1391  // first Read or Write will call it automatically.
  1392  func (c *Conn) HandshakeContext(ctx context.Context) error {
  1393  	// Delegate to unexported method for named return
  1394  	// without confusing documented signature.
  1395  	return c.handshakeContext(ctx)
  1396  }
  1397  
  1398  func (c *Conn) handshakeContext(ctx context.Context) (ret error) {
  1399  	handshakeCtx, cancel := context.WithCancel(ctx)
  1400  	// Note: defer this before starting the "interrupter" goroutine
  1401  	// so that we can tell the difference between the input being canceled and
  1402  	// this cancellation. In the former case, we need to close the connection.
  1403  	defer cancel()
  1404  
  1405  	// Start the "interrupter" goroutine, if this context might be canceled.
  1406  	// (The background context cannot).
  1407  	//
  1408  	// The interrupter goroutine waits for the input context to be done and
  1409  	// closes the connection if this happens before the function returns.
  1410  	if ctx.Done() != nil {
  1411  		done := make(chan struct{})
  1412  		interruptRes := make(chan error, 1)
  1413  		defer func() {
  1414  			close(done)
  1415  			if ctxErr := <-interruptRes; ctxErr != nil {
  1416  				// Return context error to user.
  1417  				ret = ctxErr
  1418  			}
  1419  		}()
  1420  		go func() {
  1421  			select {
  1422  			case <-handshakeCtx.Done():
  1423  				// Close the connection, discarding the error
  1424  				_ = c.conn.Close()
  1425  				interruptRes <- handshakeCtx.Err()
  1426  			case <-done:
  1427  				interruptRes <- nil
  1428  			}
  1429  		}()
  1430  	}
  1431  
  1432  	c.handshakeMutex.Lock()
  1433  	defer c.handshakeMutex.Unlock()
  1434  
  1435  	if err := c.handshakeErr; err != nil {
  1436  		return err
  1437  	}
  1438  	if c.handshakeComplete() {
  1439  		return nil
  1440  	}
  1441  
  1442  	c.in.Lock()
  1443  	defer c.in.Unlock()
  1444  
  1445  	c.handshakeErr = c.handshakeFn(handshakeCtx)
  1446  	if c.handshakeErr == nil {
  1447  		c.handshakes++
  1448  	} else {
  1449  		// If an error occurred during the handshake try to flush the
  1450  		// alert that might be left in the buffer.
  1451  		c.flush()
  1452  	}
  1453  
  1454  	if c.handshakeErr == nil && !c.handshakeComplete() {
  1455  		c.handshakeErr = errors.New("tls: internal error: handshake should have had a result")
  1456  	}
  1457  
  1458  	return c.handshakeErr
  1459  }
  1460  
  1461  // ConnectionState returns basic TLS details about the connection.
  1462  func (c *Conn) ConnectionState() ConnectionState {
  1463  	c.handshakeMutex.Lock()
  1464  	defer c.handshakeMutex.Unlock()
  1465  	return c.connectionStateLocked()
  1466  }
  1467  
  1468  func (c *Conn) connectionStateLocked() ConnectionState {
  1469  	var state ConnectionState
  1470  	state.HandshakeComplete = c.handshakeComplete()
  1471  	state.Version = c.vers
  1472  	state.NegotiatedProtocol = c.clientProtocol
  1473  	state.DidResume = c.didResume
  1474  	state.NegotiatedProtocolIsMutual = true
  1475  	state.ServerName = c.serverName
  1476  	state.CipherSuite = c.cipherSuite
  1477  	state.PeerCertificates = c.peerCertificates
  1478  	state.VerifiedChains = c.verifiedChains
  1479  	state.SignedCertificateTimestamps = c.scts
  1480  	state.OCSPResponse = c.ocspResponse
  1481  	if !c.didResume && c.vers != VersionTLS13 {
  1482  		if c.clientFinishedIsFirst {
  1483  			state.TLSUnique = c.clientFinished[:]
  1484  		} else {
  1485  			state.TLSUnique = c.serverFinished[:]
  1486  		}
  1487  	}
  1488  	if c.config.Renegotiation != RenegotiateNever {
  1489  		state.ekm = noExportedKeyingMaterial
  1490  	} else {
  1491  		state.ekm = c.ekm
  1492  	}
  1493  	return state
  1494  }
  1495  
  1496  // OCSPResponse returns the stapled OCSP response from the TLS server, if
  1497  // any. (Only valid for client connections.)
  1498  func (c *Conn) OCSPResponse() []byte {
  1499  	c.handshakeMutex.Lock()
  1500  	defer c.handshakeMutex.Unlock()
  1501  
  1502  	return c.ocspResponse
  1503  }
  1504  
  1505  // VerifyHostname checks that the peer certificate chain is valid for
  1506  // connecting to host. If so, it returns nil; if not, it returns an error
  1507  // describing the problem.
  1508  func (c *Conn) VerifyHostname(host string) error {
  1509  	c.handshakeMutex.Lock()
  1510  	defer c.handshakeMutex.Unlock()
  1511  	if !c.isClient {
  1512  		return errors.New("tls: VerifyHostname called on TLS server connection")
  1513  	}
  1514  	if !c.handshakeComplete() {
  1515  		return errors.New("tls: handshake has not yet been performed")
  1516  	}
  1517  	if len(c.verifiedChains) == 0 {
  1518  		return errors.New("tls: handshake did not verify certificate chain")
  1519  	}
  1520  	return c.peerCertificates[0].VerifyHostname(host)
  1521  }
  1522  
  1523  func (c *Conn) handshakeComplete() bool {
  1524  	return atomic.LoadUint32(&c.handshakeStatus) == 1
  1525  }
  1526  

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