Source file src/crypto/tls/conn.go

     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  	quic        *quicState                  // nil for non-QUIC connections
    33  
    34  	// isHandshakeComplete is true if the connection is currently transferring
    35  	// application data (i.e. is not currently processing a handshake).
    36  	// isHandshakeComplete is true implies handshakeErr == nil.
    37  	isHandshakeComplete atomic.Bool
    38  	// constant after handshake; protected by handshakeMutex
    39  	handshakeMutex sync.Mutex
    40  	handshakeErr   error   // error resulting from handshake
    41  	vers           uint16  // TLS version
    42  	haveVers       bool    // version has been negotiated
    43  	config         *Config // configuration passed to constructor
    44  	// handshakes counts the number of handshakes performed on the
    45  	// connection so far. If renegotiation is disabled then this is either
    46  	// zero or one.
    47  	handshakes       int
    48  	extMasterSecret  bool
    49  	didResume        bool // whether this connection was a session resumption
    50  	cipherSuite      uint16
    51  	ocspResponse     []byte   // stapled OCSP response
    52  	scts             [][]byte // signed certificate timestamps from server
    53  	peerCertificates []*x509.Certificate
    54  	// activeCertHandles contains the cache handles to certificates in
    55  	// peerCertificates that are used to track active references.
    56  	activeCertHandles []*activeCert
    57  	// verifiedChains contains the certificate chains that we built, as
    58  	// opposed to the ones presented by the server.
    59  	verifiedChains [][]*x509.Certificate
    60  	// serverName contains the server name indicated by the client, if any.
    61  	serverName string
    62  	// secureRenegotiation is true if the server echoed the secure
    63  	// renegotiation extension. (This is meaningless as a server because
    64  	// renegotiation is not supported in that case.)
    65  	secureRenegotiation bool
    66  	// ekm is a closure for exporting keying material.
    67  	ekm func(label string, context []byte, length int) ([]byte, error)
    68  	// resumptionSecret is the resumption_master_secret for handling
    69  	// or sending NewSessionTicket messages.
    70  	resumptionSecret []byte
    71  
    72  	// ticketKeys is the set of active session ticket keys for this
    73  	// connection. The first one is used to encrypt new tickets and
    74  	// all are tried to decrypt tickets.
    75  	ticketKeys []ticketKey
    76  
    77  	// clientFinishedIsFirst is true if the client sent the first Finished
    78  	// message during the most recent handshake. This is recorded because
    79  	// the first transmitted Finished message is the tls-unique
    80  	// channel-binding value.
    81  	clientFinishedIsFirst bool
    82  
    83  	// closeNotifyErr is any error from sending the alertCloseNotify record.
    84  	closeNotifyErr error
    85  	// closeNotifySent is true if the Conn attempted to send an
    86  	// alertCloseNotify record.
    87  	closeNotifySent bool
    88  
    89  	// clientFinished and serverFinished contain the Finished message sent
    90  	// by the client or server in the most recent handshake. This is
    91  	// retained to support the renegotiation extension and tls-unique
    92  	// channel-binding.
    93  	clientFinished [12]byte
    94  	serverFinished [12]byte
    95  
    96  	// clientProtocol is the negotiated ALPN protocol.
    97  	clientProtocol string
    98  
    99  	// input/output
   100  	in, out   halfConn
   101  	rawInput  bytes.Buffer // raw input, starting with a record header
   102  	input     bytes.Reader // application data waiting to be read, from rawInput.Next
   103  	hand      bytes.Buffer // handshake data waiting to be read
   104  	buffering bool         // whether records are buffered in sendBuf
   105  	sendBuf   []byte       // a buffer of records waiting to be sent
   106  
   107  	// bytesSent counts the bytes of application data sent.
   108  	// packetsSent counts packets.
   109  	bytesSent   int64
   110  	packetsSent int64
   111  
   112  	// retryCount counts the number of consecutive non-advancing records
   113  	// received by Conn.readRecord. That is, records that neither advance the
   114  	// handshake, nor deliver application data. Protected by in.Mutex.
   115  	retryCount int
   116  
   117  	// activeCall indicates whether Close has been call in the low bit.
   118  	// the rest of the bits are the number of goroutines in Conn.Write.
   119  	activeCall atomic.Int32
   120  
   121  	tmp [16]byte
   122  }
   123  
   124  // Access to net.Conn methods.
   125  // Cannot just embed net.Conn because that would
   126  // export the struct field too.
   127  
   128  // LocalAddr returns the local network address.
   129  func (c *Conn) LocalAddr() net.Addr {
   130  	return c.conn.LocalAddr()
   131  }
   132  
   133  // RemoteAddr returns the remote network address.
   134  func (c *Conn) RemoteAddr() net.Addr {
   135  	return c.conn.RemoteAddr()
   136  }
   137  
   138  // SetDeadline sets the read and write deadlines associated with the connection.
   139  // A zero value for t means Read and Write will not time out.
   140  // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
   141  func (c *Conn) SetDeadline(t time.Time) error {
   142  	return c.conn.SetDeadline(t)
   143  }
   144  
   145  // SetReadDeadline sets the read deadline on the underlying connection.
   146  // A zero value for t means Read will not time out.
   147  func (c *Conn) SetReadDeadline(t time.Time) error {
   148  	return c.conn.SetReadDeadline(t)
   149  }
   150  
   151  // SetWriteDeadline sets the write deadline on the underlying connection.
   152  // A zero value for t means Write will not time out.
   153  // After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
   154  func (c *Conn) SetWriteDeadline(t time.Time) error {
   155  	return c.conn.SetWriteDeadline(t)
   156  }
   157  
   158  // NetConn returns the underlying connection that is wrapped by c.
   159  // Note that writing to or reading from this connection directly will corrupt the
   160  // TLS session.
   161  func (c *Conn) NetConn() net.Conn {
   162  	return c.conn
   163  }
   164  
   165  // A halfConn represents one direction of the record layer
   166  // connection, either sending or receiving.
   167  type halfConn struct {
   168  	sync.Mutex
   169  
   170  	err     error  // first permanent error
   171  	version uint16 // protocol version
   172  	cipher  any    // cipher algorithm
   173  	mac     hash.Hash
   174  	seq     [8]byte // 64-bit sequence number
   175  
   176  	scratchBuf [13]byte // to avoid allocs; interface method args escape
   177  
   178  	nextCipher any       // next encryption state
   179  	nextMac    hash.Hash // next MAC algorithm
   180  
   181  	level         QUICEncryptionLevel // current QUIC encryption level
   182  	trafficSecret []byte              // current TLS 1.3 traffic secret
   183  }
   184  
   185  type permanentError struct {
   186  	err net.Error
   187  }
   188  
   189  func (e *permanentError) Error() string   { return e.err.Error() }
   190  func (e *permanentError) Unwrap() error   { return e.err }
   191  func (e *permanentError) Timeout() bool   { return e.err.Timeout() }
   192  func (e *permanentError) Temporary() bool { return false }
   193  
   194  func (hc *halfConn) setErrorLocked(err error) error {
   195  	if e, ok := err.(net.Error); ok {
   196  		hc.err = &permanentError{err: e}
   197  	} else {
   198  		hc.err = err
   199  	}
   200  	return hc.err
   201  }
   202  
   203  // prepareCipherSpec sets the encryption and MAC states
   204  // that a subsequent changeCipherSpec will use.
   205  func (hc *halfConn) prepareCipherSpec(version uint16, cipher any, mac hash.Hash) {
   206  	hc.version = version
   207  	hc.nextCipher = cipher
   208  	hc.nextMac = mac
   209  }
   210  
   211  // changeCipherSpec changes the encryption and MAC states
   212  // to the ones previously passed to prepareCipherSpec.
   213  func (hc *halfConn) changeCipherSpec() error {
   214  	if hc.nextCipher == nil || hc.version == VersionTLS13 {
   215  		return alertInternalError
   216  	}
   217  	hc.cipher = hc.nextCipher
   218  	hc.mac = hc.nextMac
   219  	hc.nextCipher = nil
   220  	hc.nextMac = nil
   221  	for i := range hc.seq {
   222  		hc.seq[i] = 0
   223  	}
   224  	return nil
   225  }
   226  
   227  func (hc *halfConn) setTrafficSecret(suite *cipherSuiteTLS13, level QUICEncryptionLevel, secret []byte) {
   228  	hc.trafficSecret = secret
   229  	hc.level = level
   230  	key, iv := suite.trafficKey(secret)
   231  	hc.cipher = suite.aead(key, iv)
   232  	for i := range hc.seq {
   233  		hc.seq[i] = 0
   234  	}
   235  }
   236  
   237  // incSeq increments the sequence number.
   238  func (hc *halfConn) incSeq() {
   239  	for i := 7; i >= 0; i-- {
   240  		hc.seq[i]++
   241  		if hc.seq[i] != 0 {
   242  			return
   243  		}
   244  	}
   245  
   246  	// Not allowed to let sequence number wrap.
   247  	// Instead, must renegotiate before it does.
   248  	// Not likely enough to bother.
   249  	panic("TLS: sequence number wraparound")
   250  }
   251  
   252  // explicitNonceLen returns the number of bytes of explicit nonce or IV included
   253  // in each record. Explicit nonces are present only in CBC modes after TLS 1.0
   254  // and in certain AEAD modes in TLS 1.2.
   255  func (hc *halfConn) explicitNonceLen() int {
   256  	if hc.cipher == nil {
   257  		return 0
   258  	}
   259  
   260  	switch c := hc.cipher.(type) {
   261  	case cipher.Stream:
   262  		return 0
   263  	case aead:
   264  		return c.explicitNonceLen()
   265  	case cbcMode:
   266  		// TLS 1.1 introduced a per-record explicit IV to fix the BEAST attack.
   267  		if hc.version >= VersionTLS11 {
   268  			return c.BlockSize()
   269  		}
   270  		return 0
   271  	default:
   272  		panic("unknown cipher type")
   273  	}
   274  }
   275  
   276  // extractPadding returns, in constant time, the length of the padding to remove
   277  // from the end of payload. It also returns a byte which is equal to 255 if the
   278  // padding was valid and 0 otherwise. See RFC 2246, Section 6.2.3.2.
   279  func extractPadding(payload []byte) (toRemove int, good byte) {
   280  	if len(payload) < 1 {
   281  		return 0, 0
   282  	}
   283  
   284  	paddingLen := payload[len(payload)-1]
   285  	t := uint(len(payload)-1) - uint(paddingLen)
   286  	// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
   287  	good = byte(int32(^t) >> 31)
   288  
   289  	// The maximum possible padding length plus the actual length field
   290  	toCheck := 256
   291  	// The length of the padded data is public, so we can use an if here
   292  	if toCheck > len(payload) {
   293  		toCheck = len(payload)
   294  	}
   295  
   296  	for i := 0; i < toCheck; i++ {
   297  		t := uint(paddingLen) - uint(i)
   298  		// if i <= paddingLen then the MSB of t is zero
   299  		mask := byte(int32(^t) >> 31)
   300  		b := payload[len(payload)-1-i]
   301  		good &^= mask&paddingLen ^ mask&b
   302  	}
   303  
   304  	// We AND together the bits of good and replicate the result across
   305  	// all the bits.
   306  	good &= good << 4
   307  	good &= good << 2
   308  	good &= good << 1
   309  	good = uint8(int8(good) >> 7)
   310  
   311  	// Zero the padding length on error. This ensures any unchecked bytes
   312  	// are included in the MAC. Otherwise, an attacker that could
   313  	// distinguish MAC failures from padding failures could mount an attack
   314  	// similar to POODLE in SSL 3.0: given a good ciphertext that uses a
   315  	// full block's worth of padding, replace the final block with another
   316  	// block. If the MAC check passed but the padding check failed, the
   317  	// last byte of that block decrypted to the block size.
   318  	//
   319  	// See also macAndPaddingGood logic below.
   320  	paddingLen &= good
   321  
   322  	toRemove = int(paddingLen) + 1
   323  	return
   324  }
   325  
   326  func roundUp(a, b int) int {
   327  	return a + (b-a%b)%b
   328  }
   329  
   330  // cbcMode is an interface for block ciphers using cipher block chaining.
   331  type cbcMode interface {
   332  	cipher.BlockMode
   333  	SetIV([]byte)
   334  }
   335  
   336  // decrypt authenticates and decrypts the record if protection is active at
   337  // this stage. The returned plaintext might overlap with the input.
   338  func (hc *halfConn) decrypt(record []byte) ([]byte, recordType, error) {
   339  	var plaintext []byte
   340  	typ := recordType(record[0])
   341  	payload := record[recordHeaderLen:]
   342  
   343  	// In TLS 1.3, change_cipher_spec messages are to be ignored without being
   344  	// decrypted. See RFC 8446, Appendix D.4.
   345  	if hc.version == VersionTLS13 && typ == recordTypeChangeCipherSpec {
   346  		return payload, typ, nil
   347  	}
   348  
   349  	paddingGood := byte(255)
   350  	paddingLen := 0
   351  
   352  	explicitNonceLen := hc.explicitNonceLen()
   353  
   354  	if hc.cipher != nil {
   355  		switch c := hc.cipher.(type) {
   356  		case cipher.Stream:
   357  			c.XORKeyStream(payload, payload)
   358  		case aead:
   359  			if len(payload) < explicitNonceLen {
   360  				return nil, 0, alertBadRecordMAC
   361  			}
   362  			nonce := payload[:explicitNonceLen]
   363  			if len(nonce) == 0 {
   364  				nonce = hc.seq[:]
   365  			}
   366  			payload = payload[explicitNonceLen:]
   367  
   368  			var additionalData []byte
   369  			if hc.version == VersionTLS13 {
   370  				additionalData = record[:recordHeaderLen]
   371  			} else {
   372  				additionalData = append(hc.scratchBuf[:0], hc.seq[:]...)
   373  				additionalData = append(additionalData, record[:3]...)
   374  				n := len(payload) - c.Overhead()
   375  				additionalData = append(additionalData, byte(n>>8), byte(n))
   376  			}
   377  
   378  			var err error
   379  			plaintext, err = c.Open(payload[:0], nonce, payload, additionalData)
   380  			if err != nil {
   381  				return nil, 0, alertBadRecordMAC
   382  			}
   383  		case cbcMode:
   384  			blockSize := c.BlockSize()
   385  			minPayload := explicitNonceLen + roundUp(hc.mac.Size()+1, blockSize)
   386  			if len(payload)%blockSize != 0 || len(payload) < minPayload {
   387  				return nil, 0, alertBadRecordMAC
   388  			}
   389  
   390  			if explicitNonceLen > 0 {
   391  				c.SetIV(payload[:explicitNonceLen])
   392  				payload = payload[explicitNonceLen:]
   393  			}
   394  			c.CryptBlocks(payload, payload)
   395  
   396  			// In a limited attempt to protect against CBC padding oracles like
   397  			// Lucky13, the data past paddingLen (which is secret) is passed to
   398  			// the MAC function as extra data, to be fed into the HMAC after
   399  			// computing the digest. This makes the MAC roughly constant time as
   400  			// long as the digest computation is constant time and does not
   401  			// affect the subsequent write, modulo cache effects.
   402  			paddingLen, paddingGood = extractPadding(payload)
   403  		default:
   404  			panic("unknown cipher type")
   405  		}
   406  
   407  		if hc.version == VersionTLS13 {
   408  			if typ != recordTypeApplicationData {
   409  				return nil, 0, alertUnexpectedMessage
   410  			}
   411  			if len(plaintext) > maxPlaintext+1 {
   412  				return nil, 0, alertRecordOverflow
   413  			}
   414  			// Remove padding and find the ContentType scanning from the end.
   415  			for i := len(plaintext) - 1; i >= 0; i-- {
   416  				if plaintext[i] != 0 {
   417  					typ = recordType(plaintext[i])
   418  					plaintext = plaintext[:i]
   419  					break
   420  				}
   421  				if i == 0 {
   422  					return nil, 0, alertUnexpectedMessage
   423  				}
   424  			}
   425  		}
   426  	} else {
   427  		plaintext = payload
   428  	}
   429  
   430  	if hc.mac != nil {
   431  		macSize := hc.mac.Size()
   432  		if len(payload) < macSize {
   433  			return nil, 0, alertBadRecordMAC
   434  		}
   435  
   436  		n := len(payload) - macSize - paddingLen
   437  		n = subtle.ConstantTimeSelect(int(uint32(n)>>31), 0, n) // if n < 0 { n = 0 }
   438  		record[3] = byte(n >> 8)
   439  		record[4] = byte(n)
   440  		remoteMAC := payload[n : n+macSize]
   441  		localMAC := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload[:n], payload[n+macSize:])
   442  
   443  		// This is equivalent to checking the MACs and paddingGood
   444  		// separately, but in constant-time to prevent distinguishing
   445  		// padding failures from MAC failures. Depending on what value
   446  		// of paddingLen was returned on bad padding, distinguishing
   447  		// bad MAC from bad padding can lead to an attack.
   448  		//
   449  		// See also the logic at the end of extractPadding.
   450  		macAndPaddingGood := subtle.ConstantTimeCompare(localMAC, remoteMAC) & int(paddingGood)
   451  		if macAndPaddingGood != 1 {
   452  			return nil, 0, alertBadRecordMAC
   453  		}
   454  
   455  		plaintext = payload[:n]
   456  	}
   457  
   458  	hc.incSeq()
   459  	return plaintext, typ, nil
   460  }
   461  
   462  // sliceForAppend extends the input slice by n bytes. head is the full extended
   463  // slice, while tail is the appended part. If the original slice has sufficient
   464  // capacity no allocation is performed.
   465  func sliceForAppend(in []byte, n int) (head, tail []byte) {
   466  	if total := len(in) + n; cap(in) >= total {
   467  		head = in[:total]
   468  	} else {
   469  		head = make([]byte, total)
   470  		copy(head, in)
   471  	}
   472  	tail = head[len(in):]
   473  	return
   474  }
   475  
   476  // encrypt encrypts payload, adding the appropriate nonce and/or MAC, and
   477  // appends it to record, which must already contain the record header.
   478  func (hc *halfConn) encrypt(record, payload []byte, rand io.Reader) ([]byte, error) {
   479  	if hc.cipher == nil {
   480  		return append(record, payload...), nil
   481  	}
   482  
   483  	var explicitNonce []byte
   484  	if explicitNonceLen := hc.explicitNonceLen(); explicitNonceLen > 0 {
   485  		record, explicitNonce = sliceForAppend(record, explicitNonceLen)
   486  		if _, isCBC := hc.cipher.(cbcMode); !isCBC && explicitNonceLen < 16 {
   487  			// The AES-GCM construction in TLS has an explicit nonce so that the
   488  			// nonce can be random. However, the nonce is only 8 bytes which is
   489  			// too small for a secure, random nonce. Therefore we use the
   490  			// sequence number as the nonce. The 3DES-CBC construction also has
   491  			// an 8 bytes nonce but its nonces must be unpredictable (see RFC
   492  			// 5246, Appendix F.3), forcing us to use randomness. That's not
   493  			// 3DES' biggest problem anyway because the birthday bound on block
   494  			// collision is reached first due to its similarly small block size
   495  			// (see the Sweet32 attack).
   496  			copy(explicitNonce, hc.seq[:])
   497  		} else {
   498  			if _, err := io.ReadFull(rand, explicitNonce); err != nil {
   499  				return nil, err
   500  			}
   501  		}
   502  	}
   503  
   504  	var dst []byte
   505  	switch c := hc.cipher.(type) {
   506  	case cipher.Stream:
   507  		mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
   508  		record, dst = sliceForAppend(record, len(payload)+len(mac))
   509  		c.XORKeyStream(dst[:len(payload)], payload)
   510  		c.XORKeyStream(dst[len(payload):], mac)
   511  	case aead:
   512  		nonce := explicitNonce
   513  		if len(nonce) == 0 {
   514  			nonce = hc.seq[:]
   515  		}
   516  
   517  		if hc.version == VersionTLS13 {
   518  			record = append(record, payload...)
   519  
   520  			// Encrypt the actual ContentType and replace the plaintext one.
   521  			record = append(record, record[0])
   522  			record[0] = byte(recordTypeApplicationData)
   523  
   524  			n := len(payload) + 1 + c.Overhead()
   525  			record[3] = byte(n >> 8)
   526  			record[4] = byte(n)
   527  
   528  			record = c.Seal(record[:recordHeaderLen],
   529  				nonce, record[recordHeaderLen:], record[:recordHeaderLen])
   530  		} else {
   531  			additionalData := append(hc.scratchBuf[:0], hc.seq[:]...)
   532  			additionalData = append(additionalData, record[:recordHeaderLen]...)
   533  			record = c.Seal(record, nonce, payload, additionalData)
   534  		}
   535  	case cbcMode:
   536  		mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
   537  		blockSize := c.BlockSize()
   538  		plaintextLen := len(payload) + len(mac)
   539  		paddingLen := blockSize - plaintextLen%blockSize
   540  		record, dst = sliceForAppend(record, plaintextLen+paddingLen)
   541  		copy(dst, payload)
   542  		copy(dst[len(payload):], mac)
   543  		for i := plaintextLen; i < len(dst); i++ {
   544  			dst[i] = byte(paddingLen - 1)
   545  		}
   546  		if len(explicitNonce) > 0 {
   547  			c.SetIV(explicitNonce)
   548  		}
   549  		c.CryptBlocks(dst, dst)
   550  	default:
   551  		panic("unknown cipher type")
   552  	}
   553  
   554  	// Update length to include nonce, MAC and any block padding needed.
   555  	n := len(record) - recordHeaderLen
   556  	record[3] = byte(n >> 8)
   557  	record[4] = byte(n)
   558  	hc.incSeq()
   559  
   560  	return record, nil
   561  }
   562  
   563  // RecordHeaderError is returned when a TLS record header is invalid.
   564  type RecordHeaderError struct {
   565  	// Msg contains a human readable string that describes the error.
   566  	Msg string
   567  	// RecordHeader contains the five bytes of TLS record header that
   568  	// triggered the error.
   569  	RecordHeader [5]byte
   570  	// Conn provides the underlying net.Conn in the case that a client
   571  	// sent an initial handshake that didn't look like TLS.
   572  	// It is nil if there's already been a handshake or a TLS alert has
   573  	// been written to the connection.
   574  	Conn net.Conn
   575  }
   576  
   577  func (e RecordHeaderError) Error() string { return "tls: " + e.Msg }
   578  
   579  func (c *Conn) newRecordHeaderError(conn net.Conn, msg string) (err RecordHeaderError) {
   580  	err.Msg = msg
   581  	err.Conn = conn
   582  	copy(err.RecordHeader[:], c.rawInput.Bytes())
   583  	return err
   584  }
   585  
   586  func (c *Conn) readRecord() error {
   587  	return c.readRecordOrCCS(false)
   588  }
   589  
   590  func (c *Conn) readChangeCipherSpec() error {
   591  	return c.readRecordOrCCS(true)
   592  }
   593  
   594  // readRecordOrCCS reads one or more TLS records from the connection and
   595  // updates the record layer state. Some invariants:
   596  //   - c.in must be locked
   597  //   - c.input must be empty
   598  //
   599  // During the handshake one and only one of the following will happen:
   600  //   - c.hand grows
   601  //   - c.in.changeCipherSpec is called
   602  //   - an error is returned
   603  //
   604  // After the handshake one and only one of the following will happen:
   605  //   - c.hand grows
   606  //   - c.input is set
   607  //   - an error is returned
   608  func (c *Conn) readRecordOrCCS(expectChangeCipherSpec bool) error {
   609  	if c.in.err != nil {
   610  		return c.in.err
   611  	}
   612  	handshakeComplete := c.isHandshakeComplete.Load()
   613  
   614  	// This function modifies c.rawInput, which owns the c.input memory.
   615  	if c.input.Len() != 0 {
   616  		return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with pending application data"))
   617  	}
   618  	c.input.Reset(nil)
   619  
   620  	if c.quic != nil {
   621  		return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with QUIC transport"))
   622  	}
   623  
   624  	// Read header, payload.
   625  	if err := c.readFromUntil(c.conn, recordHeaderLen); err != nil {
   626  		// RFC 8446, Section 6.1 suggests that EOF without an alertCloseNotify
   627  		// is an error, but popular web sites seem to do this, so we accept it
   628  		// if and only if at the record boundary.
   629  		if err == io.ErrUnexpectedEOF && c.rawInput.Len() == 0 {
   630  			err = io.EOF
   631  		}
   632  		if e, ok := err.(net.Error); !ok || !e.Temporary() {
   633  			c.in.setErrorLocked(err)
   634  		}
   635  		return err
   636  	}
   637  	hdr := c.rawInput.Bytes()[:recordHeaderLen]
   638  	typ := recordType(hdr[0])
   639  
   640  	// No valid TLS record has a type of 0x80, however SSLv2 handshakes
   641  	// start with a uint16 length where the MSB is set and the first record
   642  	// is always < 256 bytes long. Therefore typ == 0x80 strongly suggests
   643  	// an SSLv2 client.
   644  	if !handshakeComplete && typ == 0x80 {
   645  		c.sendAlert(alertProtocolVersion)
   646  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, "unsupported SSLv2 handshake received"))
   647  	}
   648  
   649  	vers := uint16(hdr[1])<<8 | uint16(hdr[2])
   650  	expectedVers := c.vers
   651  	if expectedVers == VersionTLS13 {
   652  		// All TLS 1.3 records are expected to have 0x0303 (1.2) after
   653  		// the initial hello (RFC 8446 Section 5.1).
   654  		expectedVers = VersionTLS12
   655  	}
   656  	n := int(hdr[3])<<8 | int(hdr[4])
   657  	if c.haveVers && vers != expectedVers {
   658  		c.sendAlert(alertProtocolVersion)
   659  		msg := fmt.Sprintf("received record with version %x when expecting version %x", vers, expectedVers)
   660  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
   661  	}
   662  	if !c.haveVers {
   663  		// First message, be extra suspicious: this might not be a TLS
   664  		// client. Bail out before reading a full 'body', if possible.
   665  		// The current max version is 3.3 so if the version is >= 16.0,
   666  		// it's probably not real.
   667  		if (typ != recordTypeAlert && typ != recordTypeHandshake) || vers >= 0x1000 {
   668  			return c.in.setErrorLocked(c.newRecordHeaderError(c.conn, "first record does not look like a TLS handshake"))
   669  		}
   670  	}
   671  	if c.vers == VersionTLS13 && n > maxCiphertextTLS13 || n > maxCiphertext {
   672  		c.sendAlert(alertRecordOverflow)
   673  		msg := fmt.Sprintf("oversized record received with length %d", n)
   674  		return c.in.setErrorLocked(c.newRecordHeaderError(nil, msg))
   675  	}
   676  	if err := c.readFromUntil(c.conn, recordHeaderLen+n); err != nil {
   677  		if e, ok := err.(net.Error); !ok || !e.Temporary() {
   678  			c.in.setErrorLocked(err)
   679  		}
   680  		return err
   681  	}
   682  
   683  	// Process message.
   684  	record := c.rawInput.Next(recordHeaderLen + n)
   685  	data, typ, err := c.in.decrypt(record)
   686  	if err != nil {
   687  		return c.in.setErrorLocked(c.sendAlert(err.(alert)))
   688  	}
   689  	if len(data) > maxPlaintext {
   690  		return c.in.setErrorLocked(c.sendAlert(alertRecordOverflow))
   691  	}
   692  
   693  	// Application Data messages are always protected.
   694  	if c.in.cipher == nil && typ == recordTypeApplicationData {
   695  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   696  	}
   697  
   698  	if typ != recordTypeAlert && typ != recordTypeChangeCipherSpec && len(data) > 0 {
   699  		// This is a state-advancing message: reset the retry count.
   700  		c.retryCount = 0
   701  	}
   702  
   703  	// Handshake messages MUST NOT be interleaved with other record types in TLS 1.3.
   704  	if c.vers == VersionTLS13 && typ != recordTypeHandshake && c.hand.Len() > 0 {
   705  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   706  	}
   707  
   708  	switch typ {
   709  	default:
   710  		return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   711  
   712  	case recordTypeAlert:
   713  		if c.quic != nil {
   714  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   715  		}
   716  		if len(data) != 2 {
   717  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   718  		}
   719  		if alert(data[1]) == alertCloseNotify {
   720  			return c.in.setErrorLocked(io.EOF)
   721  		}
   722  		if c.vers == VersionTLS13 {
   723  			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   724  		}
   725  		switch data[0] {
   726  		case alertLevelWarning:
   727  			// Drop the record on the floor and retry.
   728  			return c.retryReadRecord(expectChangeCipherSpec)
   729  		case alertLevelError:
   730  			return c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   731  		default:
   732  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   733  		}
   734  
   735  	case recordTypeChangeCipherSpec:
   736  		if len(data) != 1 || data[0] != 1 {
   737  			return c.in.setErrorLocked(c.sendAlert(alertDecodeError))
   738  		}
   739  		// Handshake messages are not allowed to fragment across the CCS.
   740  		if c.hand.Len() > 0 {
   741  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   742  		}
   743  		// In TLS 1.3, change_cipher_spec records are ignored until the
   744  		// Finished. See RFC 8446, Appendix D.4. Note that according to Section
   745  		// 5, a server can send a ChangeCipherSpec before its ServerHello, when
   746  		// c.vers is still unset. That's not useful though and suspicious if the
   747  		// server then selects a lower protocol version, so don't allow that.
   748  		if c.vers == VersionTLS13 {
   749  			return c.retryReadRecord(expectChangeCipherSpec)
   750  		}
   751  		if !expectChangeCipherSpec {
   752  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   753  		}
   754  		if err := c.in.changeCipherSpec(); err != nil {
   755  			return c.in.setErrorLocked(c.sendAlert(err.(alert)))
   756  		}
   757  
   758  	case recordTypeApplicationData:
   759  		if !handshakeComplete || expectChangeCipherSpec {
   760  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   761  		}
   762  		// Some OpenSSL servers send empty records in order to randomize the
   763  		// CBC IV. Ignore a limited number of empty records.
   764  		if len(data) == 0 {
   765  			return c.retryReadRecord(expectChangeCipherSpec)
   766  		}
   767  		// Note that data is owned by c.rawInput, following the Next call above,
   768  		// to avoid copying the plaintext. This is safe because c.rawInput is
   769  		// not read from or written to until c.input is drained.
   770  		c.input.Reset(data)
   771  
   772  	case recordTypeHandshake:
   773  		if len(data) == 0 || expectChangeCipherSpec {
   774  			return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   775  		}
   776  		c.hand.Write(data)
   777  	}
   778  
   779  	return nil
   780  }
   781  
   782  // retryReadRecord recurs into readRecordOrCCS to drop a non-advancing record, like
   783  // a warning alert, empty application_data, or a change_cipher_spec in TLS 1.3.
   784  func (c *Conn) retryReadRecord(expectChangeCipherSpec bool) error {
   785  	c.retryCount++
   786  	if c.retryCount > maxUselessRecords {
   787  		c.sendAlert(alertUnexpectedMessage)
   788  		return c.in.setErrorLocked(errors.New("tls: too many ignored records"))
   789  	}
   790  	return c.readRecordOrCCS(expectChangeCipherSpec)
   791  }
   792  
   793  // atLeastReader reads from R, stopping with EOF once at least N bytes have been
   794  // read. It is different from an io.LimitedReader in that it doesn't cut short
   795  // the last Read call, and in that it considers an early EOF an error.
   796  type atLeastReader struct {
   797  	R io.Reader
   798  	N int64
   799  }
   800  
   801  func (r *atLeastReader) Read(p []byte) (int, error) {
   802  	if r.N <= 0 {
   803  		return 0, io.EOF
   804  	}
   805  	n, err := r.R.Read(p)
   806  	r.N -= int64(n) // won't underflow unless len(p) >= n > 9223372036854775809
   807  	if r.N > 0 && err == io.EOF {
   808  		return n, io.ErrUnexpectedEOF
   809  	}
   810  	if r.N <= 0 && err == nil {
   811  		return n, io.EOF
   812  	}
   813  	return n, err
   814  }
   815  
   816  // readFromUntil reads from r into c.rawInput until c.rawInput contains
   817  // at least n bytes or else returns an error.
   818  func (c *Conn) readFromUntil(r io.Reader, n int) error {
   819  	if c.rawInput.Len() >= n {
   820  		return nil
   821  	}
   822  	needs := n - c.rawInput.Len()
   823  	// There might be extra input waiting on the wire. Make a best effort
   824  	// attempt to fetch it so that it can be used in (*Conn).Read to
   825  	// "predict" closeNotify alerts.
   826  	c.rawInput.Grow(needs + bytes.MinRead)
   827  	_, err := c.rawInput.ReadFrom(&atLeastReader{r, int64(needs)})
   828  	return err
   829  }
   830  
   831  // sendAlertLocked sends a TLS alert message.
   832  func (c *Conn) sendAlertLocked(err alert) error {
   833  	if c.quic != nil {
   834  		return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
   835  	}
   836  
   837  	switch err {
   838  	case alertNoRenegotiation, alertCloseNotify:
   839  		c.tmp[0] = alertLevelWarning
   840  	default:
   841  		c.tmp[0] = alertLevelError
   842  	}
   843  	c.tmp[1] = byte(err)
   844  
   845  	_, writeErr := c.writeRecordLocked(recordTypeAlert, c.tmp[0:2])
   846  	if err == alertCloseNotify {
   847  		// closeNotify is a special case in that it isn't an error.
   848  		return writeErr
   849  	}
   850  
   851  	return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
   852  }
   853  
   854  // sendAlert sends a TLS alert message.
   855  func (c *Conn) sendAlert(err alert) error {
   856  	c.out.Lock()
   857  	defer c.out.Unlock()
   858  	return c.sendAlertLocked(err)
   859  }
   860  
   861  const (
   862  	// tcpMSSEstimate is a conservative estimate of the TCP maximum segment
   863  	// size (MSS). A constant is used, rather than querying the kernel for
   864  	// the actual MSS, to avoid complexity. The value here is the IPv6
   865  	// minimum MTU (1280 bytes) minus the overhead of an IPv6 header (40
   866  	// bytes) and a TCP header with timestamps (32 bytes).
   867  	tcpMSSEstimate = 1208
   868  
   869  	// recordSizeBoostThreshold is the number of bytes of application data
   870  	// sent after which the TLS record size will be increased to the
   871  	// maximum.
   872  	recordSizeBoostThreshold = 128 * 1024
   873  )
   874  
   875  // maxPayloadSizeForWrite returns the maximum TLS payload size to use for the
   876  // next application data record. There is the following trade-off:
   877  //
   878  //   - For latency-sensitive applications, such as web browsing, each TLS
   879  //     record should fit in one TCP segment.
   880  //   - For throughput-sensitive applications, such as large file transfers,
   881  //     larger TLS records better amortize framing and encryption overheads.
   882  //
   883  // A simple heuristic that works well in practice is to use small records for
   884  // the first 1MB of data, then use larger records for subsequent data, and
   885  // reset back to smaller records after the connection becomes idle. See "High
   886  // Performance Web Networking", Chapter 4, or:
   887  // https://www.igvita.com/2013/10/24/optimizing-tls-record-size-and-buffering-latency/
   888  //
   889  // In the interests of simplicity and determinism, this code does not attempt
   890  // to reset the record size once the connection is idle, however.
   891  func (c *Conn) maxPayloadSizeForWrite(typ recordType) int {
   892  	if c.config.DynamicRecordSizingDisabled || typ != recordTypeApplicationData {
   893  		return maxPlaintext
   894  	}
   895  
   896  	if c.bytesSent >= recordSizeBoostThreshold {
   897  		return maxPlaintext
   898  	}
   899  
   900  	// Subtract TLS overheads to get the maximum payload size.
   901  	payloadBytes := tcpMSSEstimate - recordHeaderLen - c.out.explicitNonceLen()
   902  	if c.out.cipher != nil {
   903  		switch ciph := c.out.cipher.(type) {
   904  		case cipher.Stream:
   905  			payloadBytes -= c.out.mac.Size()
   906  		case cipher.AEAD:
   907  			payloadBytes -= ciph.Overhead()
   908  		case cbcMode:
   909  			blockSize := ciph.BlockSize()
   910  			// The payload must fit in a multiple of blockSize, with
   911  			// room for at least one padding byte.
   912  			payloadBytes = (payloadBytes & ^(blockSize - 1)) - 1
   913  			// The MAC is appended before padding so affects the
   914  			// payload size directly.
   915  			payloadBytes -= c.out.mac.Size()
   916  		default:
   917  			panic("unknown cipher type")
   918  		}
   919  	}
   920  	if c.vers == VersionTLS13 {
   921  		payloadBytes-- // encrypted ContentType
   922  	}
   923  
   924  	// Allow packet growth in arithmetic progression up to max.
   925  	pkt := c.packetsSent
   926  	c.packetsSent++
   927  	if pkt > 1000 {
   928  		return maxPlaintext // avoid overflow in multiply below
   929  	}
   930  
   931  	n := payloadBytes * int(pkt+1)
   932  	if n > maxPlaintext {
   933  		n = maxPlaintext
   934  	}
   935  	return n
   936  }
   937  
   938  func (c *Conn) write(data []byte) (int, error) {
   939  	if c.buffering {
   940  		c.sendBuf = append(c.sendBuf, data...)
   941  		return len(data), nil
   942  	}
   943  
   944  	n, err := c.conn.Write(data)
   945  	c.bytesSent += int64(n)
   946  	return n, err
   947  }
   948  
   949  func (c *Conn) flush() (int, error) {
   950  	if len(c.sendBuf) == 0 {
   951  		return 0, nil
   952  	}
   953  
   954  	n, err := c.conn.Write(c.sendBuf)
   955  	c.bytesSent += int64(n)
   956  	c.sendBuf = nil
   957  	c.buffering = false
   958  	return n, err
   959  }
   960  
   961  // outBufPool pools the record-sized scratch buffers used by writeRecordLocked.
   962  var outBufPool = sync.Pool{
   963  	New: func() any {
   964  		return new([]byte)
   965  	},
   966  }
   967  
   968  // writeRecordLocked writes a TLS record with the given type and payload to the
   969  // connection and updates the record layer state.
   970  func (c *Conn) writeRecordLocked(typ recordType, data []byte) (int, error) {
   971  	if c.quic != nil {
   972  		if typ != recordTypeHandshake {
   973  			return 0, errors.New("tls: internal error: sending non-handshake message to QUIC transport")
   974  		}
   975  		c.quicWriteCryptoData(c.out.level, data)
   976  		if !c.buffering {
   977  			if _, err := c.flush(); err != nil {
   978  				return 0, err
   979  			}
   980  		}
   981  		return len(data), nil
   982  	}
   983  
   984  	outBufPtr := outBufPool.Get().(*[]byte)
   985  	outBuf := *outBufPtr
   986  	defer func() {
   987  		// You might be tempted to simplify this by just passing &outBuf to Put,
   988  		// but that would make the local copy of the outBuf slice header escape
   989  		// to the heap, causing an allocation. Instead, we keep around the
   990  		// pointer to the slice header returned by Get, which is already on the
   991  		// heap, and overwrite and return that.
   992  		*outBufPtr = outBuf
   993  		outBufPool.Put(outBufPtr)
   994  	}()
   995  
   996  	var n int
   997  	for len(data) > 0 {
   998  		m := len(data)
   999  		if maxPayload := c.maxPayloadSizeForWrite(typ); m > maxPayload {
  1000  			m = maxPayload
  1001  		}
  1002  
  1003  		_, outBuf = sliceForAppend(outBuf[:0], recordHeaderLen)
  1004  		outBuf[0] = byte(typ)
  1005  		vers := c.vers
  1006  		if vers == 0 {
  1007  			// Some TLS servers fail if the record version is
  1008  			// greater than TLS 1.0 for the initial ClientHello.
  1009  			vers = VersionTLS10
  1010  		} else if vers == VersionTLS13 {
  1011  			// TLS 1.3 froze the record layer version to 1.2.
  1012  			// See RFC 8446, Section 5.1.
  1013  			vers = VersionTLS12
  1014  		}
  1015  		outBuf[1] = byte(vers >> 8)
  1016  		outBuf[2] = byte(vers)
  1017  		outBuf[3] = byte(m >> 8)
  1018  		outBuf[4] = byte(m)
  1019  
  1020  		var err error
  1021  		outBuf, err = c.out.encrypt(outBuf, data[:m], c.config.rand())
  1022  		if err != nil {
  1023  			return n, err
  1024  		}
  1025  		if _, err := c.write(outBuf); err != nil {
  1026  			return n, err
  1027  		}
  1028  		n += m
  1029  		data = data[m:]
  1030  	}
  1031  
  1032  	if typ == recordTypeChangeCipherSpec && c.vers != VersionTLS13 {
  1033  		if err := c.out.changeCipherSpec(); err != nil {
  1034  			return n, c.sendAlertLocked(err.(alert))
  1035  		}
  1036  	}
  1037  
  1038  	return n, nil
  1039  }
  1040  
  1041  // writeHandshakeRecord writes a handshake message to the connection and updates
  1042  // the record layer state. If transcript is non-nil the marshalled message is
  1043  // written to it.
  1044  func (c *Conn) writeHandshakeRecord(msg handshakeMessage, transcript transcriptHash) (int, error) {
  1045  	c.out.Lock()
  1046  	defer c.out.Unlock()
  1047  
  1048  	data, err := msg.marshal()
  1049  	if err != nil {
  1050  		return 0, err
  1051  	}
  1052  	if transcript != nil {
  1053  		transcript.Write(data)
  1054  	}
  1055  
  1056  	return c.writeRecordLocked(recordTypeHandshake, data)
  1057  }
  1058  
  1059  // writeChangeCipherRecord writes a ChangeCipherSpec message to the connection and
  1060  // updates the record layer state.
  1061  func (c *Conn) writeChangeCipherRecord() error {
  1062  	c.out.Lock()
  1063  	defer c.out.Unlock()
  1064  	_, err := c.writeRecordLocked(recordTypeChangeCipherSpec, []byte{1})
  1065  	return err
  1066  }
  1067  
  1068  // readHandshakeBytes reads handshake data until c.hand contains at least n bytes.
  1069  func (c *Conn) readHandshakeBytes(n int) error {
  1070  	if c.quic != nil {
  1071  		return c.quicReadHandshakeBytes(n)
  1072  	}
  1073  	for c.hand.Len() < n {
  1074  		if err := c.readRecord(); err != nil {
  1075  			return err
  1076  		}
  1077  	}
  1078  	return nil
  1079  }
  1080  
  1081  // readHandshake reads the next handshake message from
  1082  // the record layer. If transcript is non-nil, the message
  1083  // is written to the passed transcriptHash.
  1084  func (c *Conn) readHandshake(transcript transcriptHash) (any, error) {
  1085  	if err := c.readHandshakeBytes(4); err != nil {
  1086  		return nil, err
  1087  	}
  1088  	data := c.hand.Bytes()
  1089  	n := int(data[1])<<16 | int(data[2])<<8 | int(data[3])
  1090  	if n > maxHandshake {
  1091  		c.sendAlertLocked(alertInternalError)
  1092  		return nil, c.in.setErrorLocked(fmt.Errorf("tls: handshake message of length %d bytes exceeds maximum of %d bytes", n, maxHandshake))
  1093  	}
  1094  	if err := c.readHandshakeBytes(4 + n); err != nil {
  1095  		return nil, err
  1096  	}
  1097  	data = c.hand.Next(4 + n)
  1098  	return c.unmarshalHandshakeMessage(data, transcript)
  1099  }
  1100  
  1101  func (c *Conn) unmarshalHandshakeMessage(data []byte, transcript transcriptHash) (handshakeMessage, error) {
  1102  	var m handshakeMessage
  1103  	switch data[0] {
  1104  	case typeHelloRequest:
  1105  		m = new(helloRequestMsg)
  1106  	case typeClientHello:
  1107  		m = new(clientHelloMsg)
  1108  	case typeServerHello:
  1109  		m = new(serverHelloMsg)
  1110  	case typeNewSessionTicket:
  1111  		if c.vers == VersionTLS13 {
  1112  			m = new(newSessionTicketMsgTLS13)
  1113  		} else {
  1114  			m = new(newSessionTicketMsg)
  1115  		}
  1116  	case typeCertificate:
  1117  		if c.vers == VersionTLS13 {
  1118  			m = new(certificateMsgTLS13)
  1119  		} else {
  1120  			m = new(certificateMsg)
  1121  		}
  1122  	case typeCertificateRequest:
  1123  		if c.vers == VersionTLS13 {
  1124  			m = new(certificateRequestMsgTLS13)
  1125  		} else {
  1126  			m = &certificateRequestMsg{
  1127  				hasSignatureAlgorithm: c.vers >= VersionTLS12,
  1128  			}
  1129  		}
  1130  	case typeCertificateStatus:
  1131  		m = new(certificateStatusMsg)
  1132  	case typeServerKeyExchange:
  1133  		m = new(serverKeyExchangeMsg)
  1134  	case typeServerHelloDone:
  1135  		m = new(serverHelloDoneMsg)
  1136  	case typeClientKeyExchange:
  1137  		m = new(clientKeyExchangeMsg)
  1138  	case typeCertificateVerify:
  1139  		m = &certificateVerifyMsg{
  1140  			hasSignatureAlgorithm: c.vers >= VersionTLS12,
  1141  		}
  1142  	case typeFinished:
  1143  		m = new(finishedMsg)
  1144  	case typeEncryptedExtensions:
  1145  		m = new(encryptedExtensionsMsg)
  1146  	case typeEndOfEarlyData:
  1147  		m = new(endOfEarlyDataMsg)
  1148  	case typeKeyUpdate:
  1149  		m = new(keyUpdateMsg)
  1150  	default:
  1151  		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
  1152  	}
  1153  
  1154  	// The handshake message unmarshalers
  1155  	// expect to be able to keep references to data,
  1156  	// so pass in a fresh copy that won't be overwritten.
  1157  	data = append([]byte(nil), data...)
  1158  
  1159  	if !m.unmarshal(data) {
  1160  		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
  1161  	}
  1162  
  1163  	if transcript != nil {
  1164  		transcript.Write(data)
  1165  	}
  1166  
  1167  	return m, nil
  1168  }
  1169  
  1170  var (
  1171  	errShutdown = errors.New("tls: protocol is shutdown")
  1172  )
  1173  
  1174  // Write writes data to the connection.
  1175  //
  1176  // As Write calls Handshake, in order to prevent indefinite blocking a deadline
  1177  // must be set for both Read and Write before Write is called when the handshake
  1178  // has not yet completed. See SetDeadline, SetReadDeadline, and
  1179  // SetWriteDeadline.
  1180  func (c *Conn) Write(b []byte) (int, error) {
  1181  	// interlock with Close below
  1182  	for {
  1183  		x := c.activeCall.Load()
  1184  		if x&1 != 0 {
  1185  			return 0, net.ErrClosed
  1186  		}
  1187  		if c.activeCall.CompareAndSwap(x, x+2) {
  1188  			break
  1189  		}
  1190  	}
  1191  	defer c.activeCall.Add(-2)
  1192  
  1193  	if err := c.Handshake(); err != nil {
  1194  		return 0, err
  1195  	}
  1196  
  1197  	c.out.Lock()
  1198  	defer c.out.Unlock()
  1199  
  1200  	if err := c.out.err; err != nil {
  1201  		return 0, err
  1202  	}
  1203  
  1204  	if !c.isHandshakeComplete.Load() {
  1205  		return 0, alertInternalError
  1206  	}
  1207  
  1208  	if c.closeNotifySent {
  1209  		return 0, errShutdown
  1210  	}
  1211  
  1212  	// TLS 1.0 is susceptible to a chosen-plaintext
  1213  	// attack when using block mode ciphers due to predictable IVs.
  1214  	// This can be prevented by splitting each Application Data
  1215  	// record into two records, effectively randomizing the IV.
  1216  	//
  1217  	// https://www.openssl.org/~bodo/tls-cbc.txt
  1218  	// https://bugzilla.mozilla.org/show_bug.cgi?id=665814
  1219  	// https://www.imperialviolet.org/2012/01/15/beastfollowup.html
  1220  
  1221  	var m int
  1222  	if len(b) > 1 && c.vers == VersionTLS10 {
  1223  		if _, ok := c.out.cipher.(cipher.BlockMode); ok {
  1224  			n, err := c.writeRecordLocked(recordTypeApplicationData, b[:1])
  1225  			if err != nil {
  1226  				return n, c.out.setErrorLocked(err)
  1227  			}
  1228  			m, b = 1, b[1:]
  1229  		}
  1230  	}
  1231  
  1232  	n, err := c.writeRecordLocked(recordTypeApplicationData, b)
  1233  	return n + m, c.out.setErrorLocked(err)
  1234  }
  1235  
  1236  // handleRenegotiation processes a HelloRequest handshake message.
  1237  func (c *Conn) handleRenegotiation() error {
  1238  	if c.vers == VersionTLS13 {
  1239  		return errors.New("tls: internal error: unexpected renegotiation")
  1240  	}
  1241  
  1242  	msg, err := c.readHandshake(nil)
  1243  	if err != nil {
  1244  		return err
  1245  	}
  1246  
  1247  	helloReq, ok := msg.(*helloRequestMsg)
  1248  	if !ok {
  1249  		c.sendAlert(alertUnexpectedMessage)
  1250  		return unexpectedMessageError(helloReq, msg)
  1251  	}
  1252  
  1253  	if !c.isClient {
  1254  		return c.sendAlert(alertNoRenegotiation)
  1255  	}
  1256  
  1257  	switch c.config.Renegotiation {
  1258  	case RenegotiateNever:
  1259  		return c.sendAlert(alertNoRenegotiation)
  1260  	case RenegotiateOnceAsClient:
  1261  		if c.handshakes > 1 {
  1262  			return c.sendAlert(alertNoRenegotiation)
  1263  		}
  1264  	case RenegotiateFreelyAsClient:
  1265  		// Ok.
  1266  	default:
  1267  		c.sendAlert(alertInternalError)
  1268  		return errors.New("tls: unknown Renegotiation value")
  1269  	}
  1270  
  1271  	c.handshakeMutex.Lock()
  1272  	defer c.handshakeMutex.Unlock()
  1273  
  1274  	c.isHandshakeComplete.Store(false)
  1275  	if c.handshakeErr = c.clientHandshake(context.Background()); c.handshakeErr == nil {
  1276  		c.handshakes++
  1277  	}
  1278  	return c.handshakeErr
  1279  }
  1280  
  1281  // handlePostHandshakeMessage processes a handshake message arrived after the
  1282  // handshake is complete. Up to TLS 1.2, it indicates the start of a renegotiation.
  1283  func (c *Conn) handlePostHandshakeMessage() error {
  1284  	if c.vers != VersionTLS13 {
  1285  		return c.handleRenegotiation()
  1286  	}
  1287  
  1288  	msg, err := c.readHandshake(nil)
  1289  	if err != nil {
  1290  		return err
  1291  	}
  1292  	c.retryCount++
  1293  	if c.retryCount > maxUselessRecords {
  1294  		c.sendAlert(alertUnexpectedMessage)
  1295  		return c.in.setErrorLocked(errors.New("tls: too many non-advancing records"))
  1296  	}
  1297  
  1298  	switch msg := msg.(type) {
  1299  	case *newSessionTicketMsgTLS13:
  1300  		return c.handleNewSessionTicket(msg)
  1301  	case *keyUpdateMsg:
  1302  		return c.handleKeyUpdate(msg)
  1303  	}
  1304  	// The QUIC layer is supposed to treat an unexpected post-handshake CertificateRequest
  1305  	// as a QUIC-level PROTOCOL_VIOLATION error (RFC 9001, Section 4.4). Returning an
  1306  	// unexpected_message alert here doesn't provide it with enough information to distinguish
  1307  	// this condition from other unexpected messages. This is probably fine.
  1308  	c.sendAlert(alertUnexpectedMessage)
  1309  	return fmt.Errorf("tls: received unexpected handshake message of type %T", msg)
  1310  }
  1311  
  1312  func (c *Conn) handleKeyUpdate(keyUpdate *keyUpdateMsg) error {
  1313  	if c.quic != nil {
  1314  		c.sendAlert(alertUnexpectedMessage)
  1315  		return c.in.setErrorLocked(errors.New("tls: received unexpected key update message"))
  1316  	}
  1317  
  1318  	cipherSuite := cipherSuiteTLS13ByID(c.cipherSuite)
  1319  	if cipherSuite == nil {
  1320  		return c.in.setErrorLocked(c.sendAlert(alertInternalError))
  1321  	}
  1322  
  1323  	newSecret := cipherSuite.nextTrafficSecret(c.in.trafficSecret)
  1324  	c.in.setTrafficSecret(cipherSuite, QUICEncryptionLevelInitial, newSecret)
  1325  
  1326  	if keyUpdate.updateRequested {
  1327  		c.out.Lock()
  1328  		defer c.out.Unlock()
  1329  
  1330  		msg := &keyUpdateMsg{}
  1331  		msgBytes, err := msg.marshal()
  1332  		if err != nil {
  1333  			return err
  1334  		}
  1335  		_, err = c.writeRecordLocked(recordTypeHandshake, msgBytes)
  1336  		if err != nil {
  1337  			// Surface the error at the next write.
  1338  			c.out.setErrorLocked(err)
  1339  			return nil
  1340  		}
  1341  
  1342  		newSecret := cipherSuite.nextTrafficSecret(c.out.trafficSecret)
  1343  		c.out.setTrafficSecret(cipherSuite, QUICEncryptionLevelInitial, newSecret)
  1344  	}
  1345  
  1346  	return nil
  1347  }
  1348  
  1349  // Read reads data from the connection.
  1350  //
  1351  // As Read calls Handshake, in order to prevent indefinite blocking a deadline
  1352  // must be set for both Read and Write before Read is called when the handshake
  1353  // has not yet completed. See SetDeadline, SetReadDeadline, and
  1354  // SetWriteDeadline.
  1355  func (c *Conn) Read(b []byte) (int, error) {
  1356  	if err := c.Handshake(); err != nil {
  1357  		return 0, err
  1358  	}
  1359  	if len(b) == 0 {
  1360  		// Put this after Handshake, in case people were calling
  1361  		// Read(nil) for the side effect of the Handshake.
  1362  		return 0, nil
  1363  	}
  1364  
  1365  	c.in.Lock()
  1366  	defer c.in.Unlock()
  1367  
  1368  	for c.input.Len() == 0 {
  1369  		if err := c.readRecord(); err != nil {
  1370  			return 0, err
  1371  		}
  1372  		for c.hand.Len() > 0 {
  1373  			if err := c.handlePostHandshakeMessage(); err != nil {
  1374  				return 0, err
  1375  			}
  1376  		}
  1377  	}
  1378  
  1379  	n, _ := c.input.Read(b)
  1380  
  1381  	// If a close-notify alert is waiting, read it so that we can return (n,
  1382  	// EOF) instead of (n, nil), to signal to the HTTP response reading
  1383  	// goroutine that the connection is now closed. This eliminates a race
  1384  	// where the HTTP response reading goroutine would otherwise not observe
  1385  	// the EOF until its next read, by which time a client goroutine might
  1386  	// have already tried to reuse the HTTP connection for a new request.
  1387  	// See https://golang.org/cl/76400046 and https://golang.org/issue/3514
  1388  	if n != 0 && c.input.Len() == 0 && c.rawInput.Len() > 0 &&
  1389  		recordType(c.rawInput.Bytes()[0]) == recordTypeAlert {
  1390  		if err := c.readRecord(); err != nil {
  1391  			return n, err // will be io.EOF on closeNotify
  1392  		}
  1393  	}
  1394  
  1395  	return n, nil
  1396  }
  1397  
  1398  // Close closes the connection.
  1399  func (c *Conn) Close() error {
  1400  	// Interlock with Conn.Write above.
  1401  	var x int32
  1402  	for {
  1403  		x = c.activeCall.Load()
  1404  		if x&1 != 0 {
  1405  			return net.ErrClosed
  1406  		}
  1407  		if c.activeCall.CompareAndSwap(x, x|1) {
  1408  			break
  1409  		}
  1410  	}
  1411  	if x != 0 {
  1412  		// io.Writer and io.Closer should not be used concurrently.
  1413  		// If Close is called while a Write is currently in-flight,
  1414  		// interpret that as a sign that this Close is really just
  1415  		// being used to break the Write and/or clean up resources and
  1416  		// avoid sending the alertCloseNotify, which may block
  1417  		// waiting on handshakeMutex or the c.out mutex.
  1418  		return c.conn.Close()
  1419  	}
  1420  
  1421  	var alertErr error
  1422  	if c.isHandshakeComplete.Load() {
  1423  		if err := c.closeNotify(); err != nil {
  1424  			alertErr = fmt.Errorf("tls: failed to send closeNotify alert (but connection was closed anyway): %w", err)
  1425  		}
  1426  	}
  1427  
  1428  	if err := c.conn.Close(); err != nil {
  1429  		return err
  1430  	}
  1431  	return alertErr
  1432  }
  1433  
  1434  var errEarlyCloseWrite = errors.New("tls: CloseWrite called before handshake complete")
  1435  
  1436  // CloseWrite shuts down the writing side of the connection. It should only be
  1437  // called once the handshake has completed and does not call CloseWrite on the
  1438  // underlying connection. Most callers should just use Close.
  1439  func (c *Conn) CloseWrite() error {
  1440  	if !c.isHandshakeComplete.Load() {
  1441  		return errEarlyCloseWrite
  1442  	}
  1443  
  1444  	return c.closeNotify()
  1445  }
  1446  
  1447  func (c *Conn) closeNotify() error {
  1448  	c.out.Lock()
  1449  	defer c.out.Unlock()
  1450  
  1451  	if !c.closeNotifySent {
  1452  		// Set a Write Deadline to prevent possibly blocking forever.
  1453  		c.SetWriteDeadline(time.Now().Add(time.Second * 5))
  1454  		c.closeNotifyErr = c.sendAlertLocked(alertCloseNotify)
  1455  		c.closeNotifySent = true
  1456  		// Any subsequent writes will fail.
  1457  		c.SetWriteDeadline(time.Now())
  1458  	}
  1459  	return c.closeNotifyErr
  1460  }
  1461  
  1462  // Handshake runs the client or server handshake
  1463  // protocol if it has not yet been run.
  1464  //
  1465  // Most uses of this package need not call Handshake explicitly: the
  1466  // first Read or Write will call it automatically.
  1467  //
  1468  // For control over canceling or setting a timeout on a handshake, use
  1469  // HandshakeContext or the Dialer's DialContext method instead.
  1470  //
  1471  // In order to avoid denial of service attacks, the maximum RSA key size allowed
  1472  // in certificates sent by either the TLS server or client is limited to 8192
  1473  // bits. This limit can be overridden by setting tlsmaxrsasize in the GODEBUG
  1474  // environment variable (e.g. GODEBUG=tlsmaxrsasize=4096).
  1475  func (c *Conn) Handshake() error {
  1476  	return c.HandshakeContext(context.Background())
  1477  }
  1478  
  1479  // HandshakeContext runs the client or server handshake
  1480  // protocol if it has not yet been run.
  1481  //
  1482  // The provided Context must be non-nil. If the context is canceled before
  1483  // the handshake is complete, the handshake is interrupted and an error is returned.
  1484  // Once the handshake has completed, cancellation of the context will not affect the
  1485  // connection.
  1486  //
  1487  // Most uses of this package need not call HandshakeContext explicitly: the
  1488  // first Read or Write will call it automatically.
  1489  func (c *Conn) HandshakeContext(ctx context.Context) error {
  1490  	// Delegate to unexported method for named return
  1491  	// without confusing documented signature.
  1492  	return c.handshakeContext(ctx)
  1493  }
  1494  
  1495  func (c *Conn) handshakeContext(ctx context.Context) (ret error) {
  1496  	// Fast sync/atomic-based exit if there is no handshake in flight and the
  1497  	// last one succeeded without an error. Avoids the expensive context setup
  1498  	// and mutex for most Read and Write calls.
  1499  	if c.isHandshakeComplete.Load() {
  1500  		return nil
  1501  	}
  1502  
  1503  	handshakeCtx, cancel := context.WithCancel(ctx)
  1504  	// Note: defer this before starting the "interrupter" goroutine
  1505  	// so that we can tell the difference between the input being canceled and
  1506  	// this cancellation. In the former case, we need to close the connection.
  1507  	defer cancel()
  1508  
  1509  	if c.quic != nil {
  1510  		c.quic.cancelc = handshakeCtx.Done()
  1511  		c.quic.cancel = cancel
  1512  	} else if ctx.Done() != nil {
  1513  		// Start the "interrupter" goroutine, if this context might be canceled.
  1514  		// (The background context cannot).
  1515  		//
  1516  		// The interrupter goroutine waits for the input context to be done and
  1517  		// closes the connection if this happens before the function returns.
  1518  		done := make(chan struct{})
  1519  		interruptRes := make(chan error, 1)
  1520  		defer func() {
  1521  			close(done)
  1522  			if ctxErr := <-interruptRes; ctxErr != nil {
  1523  				// Return context error to user.
  1524  				ret = ctxErr
  1525  			}
  1526  		}()
  1527  		go func() {
  1528  			select {
  1529  			case <-handshakeCtx.Done():
  1530  				// Close the connection, discarding the error
  1531  				_ = c.conn.Close()
  1532  				interruptRes <- handshakeCtx.Err()
  1533  			case <-done:
  1534  				interruptRes <- nil
  1535  			}
  1536  		}()
  1537  	}
  1538  
  1539  	c.handshakeMutex.Lock()
  1540  	defer c.handshakeMutex.Unlock()
  1541  
  1542  	if err := c.handshakeErr; err != nil {
  1543  		return err
  1544  	}
  1545  	if c.isHandshakeComplete.Load() {
  1546  		return nil
  1547  	}
  1548  
  1549  	c.in.Lock()
  1550  	defer c.in.Unlock()
  1551  
  1552  	c.handshakeErr = c.handshakeFn(handshakeCtx)
  1553  	if c.handshakeErr == nil {
  1554  		c.handshakes++
  1555  	} else {
  1556  		// If an error occurred during the handshake try to flush the
  1557  		// alert that might be left in the buffer.
  1558  		c.flush()
  1559  	}
  1560  
  1561  	if c.handshakeErr == nil && !c.isHandshakeComplete.Load() {
  1562  		c.handshakeErr = errors.New("tls: internal error: handshake should have had a result")
  1563  	}
  1564  	if c.handshakeErr != nil && c.isHandshakeComplete.Load() {
  1565  		panic("tls: internal error: handshake returned an error but is marked successful")
  1566  	}
  1567  
  1568  	if c.quic != nil {
  1569  		if c.handshakeErr == nil {
  1570  			c.quicHandshakeComplete()
  1571  			// Provide the 1-RTT read secret now that the handshake is complete.
  1572  			// The QUIC layer MUST NOT decrypt 1-RTT packets prior to completing
  1573  			// the handshake (RFC 9001, Section 5.7).
  1574  			c.quicSetReadSecret(QUICEncryptionLevelApplication, c.cipherSuite, c.in.trafficSecret)
  1575  		} else {
  1576  			var a alert
  1577  			c.out.Lock()
  1578  			if !errors.As(c.out.err, &a) {
  1579  				a = alertInternalError
  1580  			}
  1581  			c.out.Unlock()
  1582  			// Return an error which wraps both the handshake error and
  1583  			// any alert error we may have sent, or alertInternalError
  1584  			// if we didn't send an alert.
  1585  			// Truncate the text of the alert to 0 characters.
  1586  			c.handshakeErr = fmt.Errorf("%w%.0w", c.handshakeErr, AlertError(a))
  1587  		}
  1588  		close(c.quic.blockedc)
  1589  		close(c.quic.signalc)
  1590  	}
  1591  
  1592  	return c.handshakeErr
  1593  }
  1594  
  1595  // ConnectionState returns basic TLS details about the connection.
  1596  func (c *Conn) ConnectionState() ConnectionState {
  1597  	c.handshakeMutex.Lock()
  1598  	defer c.handshakeMutex.Unlock()
  1599  	return c.connectionStateLocked()
  1600  }
  1601  
  1602  func (c *Conn) connectionStateLocked() ConnectionState {
  1603  	var state ConnectionState
  1604  	state.HandshakeComplete = c.isHandshakeComplete.Load()
  1605  	state.Version = c.vers
  1606  	state.NegotiatedProtocol = c.clientProtocol
  1607  	state.DidResume = c.didResume
  1608  	state.NegotiatedProtocolIsMutual = true
  1609  	state.ServerName = c.serverName
  1610  	state.CipherSuite = c.cipherSuite
  1611  	state.PeerCertificates = c.peerCertificates
  1612  	state.VerifiedChains = c.verifiedChains
  1613  	state.SignedCertificateTimestamps = c.scts
  1614  	state.OCSPResponse = c.ocspResponse
  1615  	if (!c.didResume || c.extMasterSecret) && c.vers != VersionTLS13 {
  1616  		if c.clientFinishedIsFirst {
  1617  			state.TLSUnique = c.clientFinished[:]
  1618  		} else {
  1619  			state.TLSUnique = c.serverFinished[:]
  1620  		}
  1621  	}
  1622  	if c.config.Renegotiation != RenegotiateNever {
  1623  		state.ekm = noExportedKeyingMaterial
  1624  	} else {
  1625  		state.ekm = c.ekm
  1626  	}
  1627  	return state
  1628  }
  1629  
  1630  // OCSPResponse returns the stapled OCSP response from the TLS server, if
  1631  // any. (Only valid for client connections.)
  1632  func (c *Conn) OCSPResponse() []byte {
  1633  	c.handshakeMutex.Lock()
  1634  	defer c.handshakeMutex.Unlock()
  1635  
  1636  	return c.ocspResponse
  1637  }
  1638  
  1639  // VerifyHostname checks that the peer certificate chain is valid for
  1640  // connecting to host. If so, it returns nil; if not, it returns an error
  1641  // describing the problem.
  1642  func (c *Conn) VerifyHostname(host string) error {
  1643  	c.handshakeMutex.Lock()
  1644  	defer c.handshakeMutex.Unlock()
  1645  	if !c.isClient {
  1646  		return errors.New("tls: VerifyHostname called on TLS server connection")
  1647  	}
  1648  	if !c.isHandshakeComplete.Load() {
  1649  		return errors.New("tls: handshake has not yet been performed")
  1650  	}
  1651  	if len(c.verifiedChains) == 0 {
  1652  		return errors.New("tls: handshake did not verify certificate chain")
  1653  	}
  1654  	return c.peerCertificates[0].VerifyHostname(host)
  1655  }
  1656  

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