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Source file src/pkg/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		"crypto/cipher"
    12		"crypto/subtle"
    13		"crypto/x509"
    14		"errors"
    15		"fmt"
    16		"io"
    17		"net"
    18		"sync"
    19		"time"
    20	)
    21	
    22	// A Conn represents a secured connection.
    23	// It implements the net.Conn interface.
    24	type Conn struct {
    25		// constant
    26		conn     net.Conn
    27		isClient bool
    28	
    29		// constant after handshake; protected by handshakeMutex
    30		handshakeMutex    sync.Mutex // handshakeMutex < in.Mutex, out.Mutex, errMutex
    31		handshakeErr      error      // error resulting from handshake
    32		vers              uint16     // TLS version
    33		haveVers          bool       // version has been negotiated
    34		config            *Config    // configuration passed to constructor
    35		handshakeComplete bool
    36		didResume         bool // whether this connection was a session resumption
    37		cipherSuite       uint16
    38		ocspResponse      []byte // stapled OCSP response
    39		peerCertificates  []*x509.Certificate
    40		// verifiedChains contains the certificate chains that we built, as
    41		// opposed to the ones presented by the server.
    42		verifiedChains [][]*x509.Certificate
    43		// serverName contains the server name indicated by the client, if any.
    44		serverName string
    45	
    46		clientProtocol         string
    47		clientProtocolFallback bool
    48	
    49		// input/output
    50		in, out  halfConn     // in.Mutex < out.Mutex
    51		rawInput *block       // raw input, right off the wire
    52		input    *block       // application data waiting to be read
    53		hand     bytes.Buffer // handshake data waiting to be read
    54	
    55		tmp [16]byte
    56	}
    57	
    58	// Access to net.Conn methods.
    59	// Cannot just embed net.Conn because that would
    60	// export the struct field too.
    61	
    62	// LocalAddr returns the local network address.
    63	func (c *Conn) LocalAddr() net.Addr {
    64		return c.conn.LocalAddr()
    65	}
    66	
    67	// RemoteAddr returns the remote network address.
    68	func (c *Conn) RemoteAddr() net.Addr {
    69		return c.conn.RemoteAddr()
    70	}
    71	
    72	// SetDeadline sets the read and write deadlines associated with the connection.
    73	// A zero value for t means Read and Write will not time out.
    74	// After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
    75	func (c *Conn) SetDeadline(t time.Time) error {
    76		return c.conn.SetDeadline(t)
    77	}
    78	
    79	// SetReadDeadline sets the read deadline on the underlying connection.
    80	// A zero value for t means Read will not time out.
    81	func (c *Conn) SetReadDeadline(t time.Time) error {
    82		return c.conn.SetReadDeadline(t)
    83	}
    84	
    85	// SetWriteDeadline sets the write deadline on the underlying connection.
    86	// A zero value for t means Write will not time out.
    87	// After a Write has timed out, the TLS state is corrupt and all future writes will return the same error.
    88	func (c *Conn) SetWriteDeadline(t time.Time) error {
    89		return c.conn.SetWriteDeadline(t)
    90	}
    91	
    92	// A halfConn represents one direction of the record layer
    93	// connection, either sending or receiving.
    94	type halfConn struct {
    95		sync.Mutex
    96	
    97		err     error       // first permanent error
    98		version uint16      // protocol version
    99		cipher  interface{} // cipher algorithm
   100		mac     macFunction
   101		seq     [8]byte // 64-bit sequence number
   102		bfree   *block  // list of free blocks
   103	
   104		nextCipher interface{} // next encryption state
   105		nextMac    macFunction // next MAC algorithm
   106	
   107		// used to save allocating a new buffer for each MAC.
   108		inDigestBuf, outDigestBuf []byte
   109	}
   110	
   111	func (hc *halfConn) setErrorLocked(err error) error {
   112		hc.err = err
   113		return err
   114	}
   115	
   116	func (hc *halfConn) error() error {
   117		hc.Lock()
   118		err := hc.err
   119		hc.Unlock()
   120		return err
   121	}
   122	
   123	// prepareCipherSpec sets the encryption and MAC states
   124	// that a subsequent changeCipherSpec will use.
   125	func (hc *halfConn) prepareCipherSpec(version uint16, cipher interface{}, mac macFunction) {
   126		hc.version = version
   127		hc.nextCipher = cipher
   128		hc.nextMac = mac
   129	}
   130	
   131	// changeCipherSpec changes the encryption and MAC states
   132	// to the ones previously passed to prepareCipherSpec.
   133	func (hc *halfConn) changeCipherSpec() error {
   134		if hc.nextCipher == nil {
   135			return alertInternalError
   136		}
   137		hc.cipher = hc.nextCipher
   138		hc.mac = hc.nextMac
   139		hc.nextCipher = nil
   140		hc.nextMac = nil
   141		for i := range hc.seq {
   142			hc.seq[i] = 0
   143		}
   144		return nil
   145	}
   146	
   147	// incSeq increments the sequence number.
   148	func (hc *halfConn) incSeq() {
   149		for i := 7; i >= 0; i-- {
   150			hc.seq[i]++
   151			if hc.seq[i] != 0 {
   152				return
   153			}
   154		}
   155	
   156		// Not allowed to let sequence number wrap.
   157		// Instead, must renegotiate before it does.
   158		// Not likely enough to bother.
   159		panic("TLS: sequence number wraparound")
   160	}
   161	
   162	// resetSeq resets the sequence number to zero.
   163	func (hc *halfConn) resetSeq() {
   164		for i := range hc.seq {
   165			hc.seq[i] = 0
   166		}
   167	}
   168	
   169	// removePadding returns an unpadded slice, in constant time, which is a prefix
   170	// of the input. It also returns a byte which is equal to 255 if the padding
   171	// was valid and 0 otherwise. See RFC 2246, section 6.2.3.2
   172	func removePadding(payload []byte) ([]byte, byte) {
   173		if len(payload) < 1 {
   174			return payload, 0
   175		}
   176	
   177		paddingLen := payload[len(payload)-1]
   178		t := uint(len(payload)-1) - uint(paddingLen)
   179		// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
   180		good := byte(int32(^t) >> 31)
   181	
   182		toCheck := 255 // the maximum possible padding length
   183		// The length of the padded data is public, so we can use an if here
   184		if toCheck+1 > len(payload) {
   185			toCheck = len(payload) - 1
   186		}
   187	
   188		for i := 0; i < toCheck; i++ {
   189			t := uint(paddingLen) - uint(i)
   190			// if i <= paddingLen then the MSB of t is zero
   191			mask := byte(int32(^t) >> 31)
   192			b := payload[len(payload)-1-i]
   193			good &^= mask&paddingLen ^ mask&b
   194		}
   195	
   196		// We AND together the bits of good and replicate the result across
   197		// all the bits.
   198		good &= good << 4
   199		good &= good << 2
   200		good &= good << 1
   201		good = uint8(int8(good) >> 7)
   202	
   203		toRemove := good&paddingLen + 1
   204		return payload[:len(payload)-int(toRemove)], good
   205	}
   206	
   207	// removePaddingSSL30 is a replacement for removePadding in the case that the
   208	// protocol version is SSLv3. In this version, the contents of the padding
   209	// are random and cannot be checked.
   210	func removePaddingSSL30(payload []byte) ([]byte, byte) {
   211		if len(payload) < 1 {
   212			return payload, 0
   213		}
   214	
   215		paddingLen := int(payload[len(payload)-1]) + 1
   216		if paddingLen > len(payload) {
   217			return payload, 0
   218		}
   219	
   220		return payload[:len(payload)-paddingLen], 255
   221	}
   222	
   223	func roundUp(a, b int) int {
   224		return a + (b-a%b)%b
   225	}
   226	
   227	// cbcMode is an interface for block ciphers using cipher block chaining.
   228	type cbcMode interface {
   229		cipher.BlockMode
   230		SetIV([]byte)
   231	}
   232	
   233	// decrypt checks and strips the mac and decrypts the data in b. Returns a
   234	// success boolean, the number of bytes to skip from the start of the record in
   235	// order to get the application payload, and an optional alert value.
   236	func (hc *halfConn) decrypt(b *block) (ok bool, prefixLen int, alertValue alert) {
   237		// pull out payload
   238		payload := b.data[recordHeaderLen:]
   239	
   240		macSize := 0
   241		if hc.mac != nil {
   242			macSize = hc.mac.Size()
   243		}
   244	
   245		paddingGood := byte(255)
   246		explicitIVLen := 0
   247	
   248		// decrypt
   249		if hc.cipher != nil {
   250			switch c := hc.cipher.(type) {
   251			case cipher.Stream:
   252				c.XORKeyStream(payload, payload)
   253			case cipher.AEAD:
   254				explicitIVLen = 8
   255				if len(payload) < explicitIVLen {
   256					return false, 0, alertBadRecordMAC
   257				}
   258				nonce := payload[:8]
   259				payload = payload[8:]
   260	
   261				var additionalData [13]byte
   262				copy(additionalData[:], hc.seq[:])
   263				copy(additionalData[8:], b.data[:3])
   264				n := len(payload) - c.Overhead()
   265				additionalData[11] = byte(n >> 8)
   266				additionalData[12] = byte(n)
   267				var err error
   268				payload, err = c.Open(payload[:0], nonce, payload, additionalData[:])
   269				if err != nil {
   270					return false, 0, alertBadRecordMAC
   271				}
   272				b.resize(recordHeaderLen + explicitIVLen + len(payload))
   273			case cbcMode:
   274				blockSize := c.BlockSize()
   275				if hc.version >= VersionTLS11 {
   276					explicitIVLen = blockSize
   277				}
   278	
   279				if len(payload)%blockSize != 0 || len(payload) < roundUp(explicitIVLen+macSize+1, blockSize) {
   280					return false, 0, alertBadRecordMAC
   281				}
   282	
   283				if explicitIVLen > 0 {
   284					c.SetIV(payload[:explicitIVLen])
   285					payload = payload[explicitIVLen:]
   286				}
   287				c.CryptBlocks(payload, payload)
   288				if hc.version == VersionSSL30 {
   289					payload, paddingGood = removePaddingSSL30(payload)
   290				} else {
   291					payload, paddingGood = removePadding(payload)
   292				}
   293				b.resize(recordHeaderLen + explicitIVLen + len(payload))
   294	
   295				// note that we still have a timing side-channel in the
   296				// MAC check, below. An attacker can align the record
   297				// so that a correct padding will cause one less hash
   298				// block to be calculated. Then they can iteratively
   299				// decrypt a record by breaking each byte. See
   300				// "Password Interception in a SSL/TLS Channel", Brice
   301				// Canvel et al.
   302				//
   303				// However, our behavior matches OpenSSL, so we leak
   304				// only as much as they do.
   305			default:
   306				panic("unknown cipher type")
   307			}
   308		}
   309	
   310		// check, strip mac
   311		if hc.mac != nil {
   312			if len(payload) < macSize {
   313				return false, 0, alertBadRecordMAC
   314			}
   315	
   316			// strip mac off payload, b.data
   317			n := len(payload) - macSize
   318			b.data[3] = byte(n >> 8)
   319			b.data[4] = byte(n)
   320			b.resize(recordHeaderLen + explicitIVLen + n)
   321			remoteMAC := payload[n:]
   322			localMAC := hc.mac.MAC(hc.inDigestBuf, hc.seq[0:], b.data[:recordHeaderLen], payload[:n])
   323	
   324			if subtle.ConstantTimeCompare(localMAC, remoteMAC) != 1 || paddingGood != 255 {
   325				return false, 0, alertBadRecordMAC
   326			}
   327			hc.inDigestBuf = localMAC
   328		}
   329		hc.incSeq()
   330	
   331		return true, recordHeaderLen + explicitIVLen, 0
   332	}
   333	
   334	// padToBlockSize calculates the needed padding block, if any, for a payload.
   335	// On exit, prefix aliases payload and extends to the end of the last full
   336	// block of payload. finalBlock is a fresh slice which contains the contents of
   337	// any suffix of payload as well as the needed padding to make finalBlock a
   338	// full block.
   339	func padToBlockSize(payload []byte, blockSize int) (prefix, finalBlock []byte) {
   340		overrun := len(payload) % blockSize
   341		paddingLen := blockSize - overrun
   342		prefix = payload[:len(payload)-overrun]
   343		finalBlock = make([]byte, blockSize)
   344		copy(finalBlock, payload[len(payload)-overrun:])
   345		for i := overrun; i < blockSize; i++ {
   346			finalBlock[i] = byte(paddingLen - 1)
   347		}
   348		return
   349	}
   350	
   351	// encrypt encrypts and macs the data in b.
   352	func (hc *halfConn) encrypt(b *block, explicitIVLen int) (bool, alert) {
   353		// mac
   354		if hc.mac != nil {
   355			mac := hc.mac.MAC(hc.outDigestBuf, hc.seq[0:], b.data[:recordHeaderLen], b.data[recordHeaderLen+explicitIVLen:])
   356	
   357			n := len(b.data)
   358			b.resize(n + len(mac))
   359			copy(b.data[n:], mac)
   360			hc.outDigestBuf = mac
   361		}
   362	
   363		payload := b.data[recordHeaderLen:]
   364	
   365		// encrypt
   366		if hc.cipher != nil {
   367			switch c := hc.cipher.(type) {
   368			case cipher.Stream:
   369				c.XORKeyStream(payload, payload)
   370			case cipher.AEAD:
   371				payloadLen := len(b.data) - recordHeaderLen - explicitIVLen
   372				b.resize(len(b.data) + c.Overhead())
   373				nonce := b.data[recordHeaderLen : recordHeaderLen+explicitIVLen]
   374				payload := b.data[recordHeaderLen+explicitIVLen:]
   375				payload = payload[:payloadLen]
   376	
   377				var additionalData [13]byte
   378				copy(additionalData[:], hc.seq[:])
   379				copy(additionalData[8:], b.data[:3])
   380				additionalData[11] = byte(payloadLen >> 8)
   381				additionalData[12] = byte(payloadLen)
   382	
   383				c.Seal(payload[:0], nonce, payload, additionalData[:])
   384			case cbcMode:
   385				blockSize := c.BlockSize()
   386				if explicitIVLen > 0 {
   387					c.SetIV(payload[:explicitIVLen])
   388					payload = payload[explicitIVLen:]
   389				}
   390				prefix, finalBlock := padToBlockSize(payload, blockSize)
   391				b.resize(recordHeaderLen + explicitIVLen + len(prefix) + len(finalBlock))
   392				c.CryptBlocks(b.data[recordHeaderLen+explicitIVLen:], prefix)
   393				c.CryptBlocks(b.data[recordHeaderLen+explicitIVLen+len(prefix):], finalBlock)
   394			default:
   395				panic("unknown cipher type")
   396			}
   397		}
   398	
   399		// update length to include MAC and any block padding needed.
   400		n := len(b.data) - recordHeaderLen
   401		b.data[3] = byte(n >> 8)
   402		b.data[4] = byte(n)
   403		hc.incSeq()
   404	
   405		return true, 0
   406	}
   407	
   408	// A block is a simple data buffer.
   409	type block struct {
   410		data []byte
   411		off  int // index for Read
   412		link *block
   413	}
   414	
   415	// resize resizes block to be n bytes, growing if necessary.
   416	func (b *block) resize(n int) {
   417		if n > cap(b.data) {
   418			b.reserve(n)
   419		}
   420		b.data = b.data[0:n]
   421	}
   422	
   423	// reserve makes sure that block contains a capacity of at least n bytes.
   424	func (b *block) reserve(n int) {
   425		if cap(b.data) >= n {
   426			return
   427		}
   428		m := cap(b.data)
   429		if m == 0 {
   430			m = 1024
   431		}
   432		for m < n {
   433			m *= 2
   434		}
   435		data := make([]byte, len(b.data), m)
   436		copy(data, b.data)
   437		b.data = data
   438	}
   439	
   440	// readFromUntil reads from r into b until b contains at least n bytes
   441	// or else returns an error.
   442	func (b *block) readFromUntil(r io.Reader, n int) error {
   443		// quick case
   444		if len(b.data) >= n {
   445			return nil
   446		}
   447	
   448		// read until have enough.
   449		b.reserve(n)
   450		for {
   451			m, err := r.Read(b.data[len(b.data):cap(b.data)])
   452			b.data = b.data[0 : len(b.data)+m]
   453			if len(b.data) >= n {
   454				// TODO(bradfitz,agl): slightly suspicious
   455				// that we're throwing away r.Read's err here.
   456				break
   457			}
   458			if err != nil {
   459				return err
   460			}
   461		}
   462		return nil
   463	}
   464	
   465	func (b *block) Read(p []byte) (n int, err error) {
   466		n = copy(p, b.data[b.off:])
   467		b.off += n
   468		return
   469	}
   470	
   471	// newBlock allocates a new block, from hc's free list if possible.
   472	func (hc *halfConn) newBlock() *block {
   473		b := hc.bfree
   474		if b == nil {
   475			return new(block)
   476		}
   477		hc.bfree = b.link
   478		b.link = nil
   479		b.resize(0)
   480		return b
   481	}
   482	
   483	// freeBlock returns a block to hc's free list.
   484	// The protocol is such that each side only has a block or two on
   485	// its free list at a time, so there's no need to worry about
   486	// trimming the list, etc.
   487	func (hc *halfConn) freeBlock(b *block) {
   488		b.link = hc.bfree
   489		hc.bfree = b
   490	}
   491	
   492	// splitBlock splits a block after the first n bytes,
   493	// returning a block with those n bytes and a
   494	// block with the remainder.  the latter may be nil.
   495	func (hc *halfConn) splitBlock(b *block, n int) (*block, *block) {
   496		if len(b.data) <= n {
   497			return b, nil
   498		}
   499		bb := hc.newBlock()
   500		bb.resize(len(b.data) - n)
   501		copy(bb.data, b.data[n:])
   502		b.data = b.data[0:n]
   503		return b, bb
   504	}
   505	
   506	// readRecord reads the next TLS record from the connection
   507	// and updates the record layer state.
   508	// c.in.Mutex <= L; c.input == nil.
   509	func (c *Conn) readRecord(want recordType) error {
   510		// Caller must be in sync with connection:
   511		// handshake data if handshake not yet completed,
   512		// else application data.  (We don't support renegotiation.)
   513		switch want {
   514		default:
   515			c.sendAlert(alertInternalError)
   516			return c.in.setErrorLocked(errors.New("tls: unknown record type requested"))
   517		case recordTypeHandshake, recordTypeChangeCipherSpec:
   518			if c.handshakeComplete {
   519				c.sendAlert(alertInternalError)
   520				return c.in.setErrorLocked(errors.New("tls: handshake or ChangeCipherSpec requested after handshake complete"))
   521			}
   522		case recordTypeApplicationData:
   523			if !c.handshakeComplete {
   524				c.sendAlert(alertInternalError)
   525				return c.in.setErrorLocked(errors.New("tls: application data record requested before handshake complete"))
   526			}
   527		}
   528	
   529	Again:
   530		if c.rawInput == nil {
   531			c.rawInput = c.in.newBlock()
   532		}
   533		b := c.rawInput
   534	
   535		// Read header, payload.
   536		if err := b.readFromUntil(c.conn, recordHeaderLen); err != nil {
   537			// RFC suggests that EOF without an alertCloseNotify is
   538			// an error, but popular web sites seem to do this,
   539			// so we can't make it an error.
   540			// if err == io.EOF {
   541			// 	err = io.ErrUnexpectedEOF
   542			// }
   543			if e, ok := err.(net.Error); !ok || !e.Temporary() {
   544				c.in.setErrorLocked(err)
   545			}
   546			return err
   547		}
   548		typ := recordType(b.data[0])
   549	
   550		// No valid TLS record has a type of 0x80, however SSLv2 handshakes
   551		// start with a uint16 length where the MSB is set and the first record
   552		// is always < 256 bytes long. Therefore typ == 0x80 strongly suggests
   553		// an SSLv2 client.
   554		if want == recordTypeHandshake && typ == 0x80 {
   555			c.sendAlert(alertProtocolVersion)
   556			return c.in.setErrorLocked(errors.New("tls: unsupported SSLv2 handshake received"))
   557		}
   558	
   559		vers := uint16(b.data[1])<<8 | uint16(b.data[2])
   560		n := int(b.data[3])<<8 | int(b.data[4])
   561		if c.haveVers && vers != c.vers {
   562			c.sendAlert(alertProtocolVersion)
   563			return c.in.setErrorLocked(fmt.Errorf("tls: received record with version %x when expecting version %x", vers, c.vers))
   564		}
   565		if n > maxCiphertext {
   566			c.sendAlert(alertRecordOverflow)
   567			return c.in.setErrorLocked(fmt.Errorf("tls: oversized record received with length %d", n))
   568		}
   569		if !c.haveVers {
   570			// First message, be extra suspicious:
   571			// this might not be a TLS client.
   572			// Bail out before reading a full 'body', if possible.
   573			// The current max version is 3.1.
   574			// If the version is >= 16.0, it's probably not real.
   575			// Similarly, a clientHello message encodes in
   576			// well under a kilobyte.  If the length is >= 12 kB,
   577			// it's probably not real.
   578			if (typ != recordTypeAlert && typ != want) || vers >= 0x1000 || n >= 0x3000 {
   579				c.sendAlert(alertUnexpectedMessage)
   580				return c.in.setErrorLocked(fmt.Errorf("tls: first record does not look like a TLS handshake"))
   581			}
   582		}
   583		if err := b.readFromUntil(c.conn, recordHeaderLen+n); err != nil {
   584			if err == io.EOF {
   585				err = io.ErrUnexpectedEOF
   586			}
   587			if e, ok := err.(net.Error); !ok || !e.Temporary() {
   588				c.in.setErrorLocked(err)
   589			}
   590			return err
   591		}
   592	
   593		// Process message.
   594		b, c.rawInput = c.in.splitBlock(b, recordHeaderLen+n)
   595		ok, off, err := c.in.decrypt(b)
   596		if !ok {
   597			c.in.setErrorLocked(c.sendAlert(err))
   598		}
   599		b.off = off
   600		data := b.data[b.off:]
   601		if len(data) > maxPlaintext {
   602			err := c.sendAlert(alertRecordOverflow)
   603			c.in.freeBlock(b)
   604			return c.in.setErrorLocked(err)
   605		}
   606	
   607		switch typ {
   608		default:
   609			c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   610	
   611		case recordTypeAlert:
   612			if len(data) != 2 {
   613				c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   614				break
   615			}
   616			if alert(data[1]) == alertCloseNotify {
   617				c.in.setErrorLocked(io.EOF)
   618				break
   619			}
   620			switch data[0] {
   621			case alertLevelWarning:
   622				// drop on the floor
   623				c.in.freeBlock(b)
   624				goto Again
   625			case alertLevelError:
   626				c.in.setErrorLocked(&net.OpError{Op: "remote error", Err: alert(data[1])})
   627			default:
   628				c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   629			}
   630	
   631		case recordTypeChangeCipherSpec:
   632			if typ != want || len(data) != 1 || data[0] != 1 {
   633				c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   634				break
   635			}
   636			err := c.in.changeCipherSpec()
   637			if err != nil {
   638				c.in.setErrorLocked(c.sendAlert(err.(alert)))
   639			}
   640	
   641		case recordTypeApplicationData:
   642			if typ != want {
   643				c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   644				break
   645			}
   646			c.input = b
   647			b = nil
   648	
   649		case recordTypeHandshake:
   650			// TODO(rsc): Should at least pick off connection close.
   651			if typ != want {
   652				return c.in.setErrorLocked(c.sendAlert(alertNoRenegotiation))
   653			}
   654			c.hand.Write(data)
   655		}
   656	
   657		if b != nil {
   658			c.in.freeBlock(b)
   659		}
   660		return c.in.err
   661	}
   662	
   663	// sendAlert sends a TLS alert message.
   664	// c.out.Mutex <= L.
   665	func (c *Conn) sendAlertLocked(err alert) error {
   666		switch err {
   667		case alertNoRenegotiation, alertCloseNotify:
   668			c.tmp[0] = alertLevelWarning
   669		default:
   670			c.tmp[0] = alertLevelError
   671		}
   672		c.tmp[1] = byte(err)
   673		c.writeRecord(recordTypeAlert, c.tmp[0:2])
   674		// closeNotify is a special case in that it isn't an error:
   675		if err != alertCloseNotify {
   676			return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
   677		}
   678		return nil
   679	}
   680	
   681	// sendAlert sends a TLS alert message.
   682	// L < c.out.Mutex.
   683	func (c *Conn) sendAlert(err alert) error {
   684		c.out.Lock()
   685		defer c.out.Unlock()
   686		return c.sendAlertLocked(err)
   687	}
   688	
   689	// writeRecord writes a TLS record with the given type and payload
   690	// to the connection and updates the record layer state.
   691	// c.out.Mutex <= L.
   692	func (c *Conn) writeRecord(typ recordType, data []byte) (n int, err error) {
   693		b := c.out.newBlock()
   694		for len(data) > 0 {
   695			m := len(data)
   696			if m > maxPlaintext {
   697				m = maxPlaintext
   698			}
   699			explicitIVLen := 0
   700			explicitIVIsSeq := false
   701	
   702			var cbc cbcMode
   703			if c.out.version >= VersionTLS11 {
   704				var ok bool
   705				if cbc, ok = c.out.cipher.(cbcMode); ok {
   706					explicitIVLen = cbc.BlockSize()
   707				}
   708			}
   709			if explicitIVLen == 0 {
   710				if _, ok := c.out.cipher.(cipher.AEAD); ok {
   711					explicitIVLen = 8
   712					// The AES-GCM construction in TLS has an
   713					// explicit nonce so that the nonce can be
   714					// random. However, the nonce is only 8 bytes
   715					// which is too small for a secure, random
   716					// nonce. Therefore we use the sequence number
   717					// as the nonce.
   718					explicitIVIsSeq = true
   719				}
   720			}
   721			b.resize(recordHeaderLen + explicitIVLen + m)
   722			b.data[0] = byte(typ)
   723			vers := c.vers
   724			if vers == 0 {
   725				// Some TLS servers fail if the record version is
   726				// greater than TLS 1.0 for the initial ClientHello.
   727				vers = VersionTLS10
   728			}
   729			b.data[1] = byte(vers >> 8)
   730			b.data[2] = byte(vers)
   731			b.data[3] = byte(m >> 8)
   732			b.data[4] = byte(m)
   733			if explicitIVLen > 0 {
   734				explicitIV := b.data[recordHeaderLen : recordHeaderLen+explicitIVLen]
   735				if explicitIVIsSeq {
   736					copy(explicitIV, c.out.seq[:])
   737				} else {
   738					if _, err = io.ReadFull(c.config.rand(), explicitIV); err != nil {
   739						break
   740					}
   741				}
   742			}
   743			copy(b.data[recordHeaderLen+explicitIVLen:], data)
   744			c.out.encrypt(b, explicitIVLen)
   745			_, err = c.conn.Write(b.data)
   746			if err != nil {
   747				break
   748			}
   749			n += m
   750			data = data[m:]
   751		}
   752		c.out.freeBlock(b)
   753	
   754		if typ == recordTypeChangeCipherSpec {
   755			err = c.out.changeCipherSpec()
   756			if err != nil {
   757				// Cannot call sendAlert directly,
   758				// because we already hold c.out.Mutex.
   759				c.tmp[0] = alertLevelError
   760				c.tmp[1] = byte(err.(alert))
   761				c.writeRecord(recordTypeAlert, c.tmp[0:2])
   762				return n, c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
   763			}
   764		}
   765		return
   766	}
   767	
   768	// readHandshake reads the next handshake message from
   769	// the record layer.
   770	// c.in.Mutex < L; c.out.Mutex < L.
   771	func (c *Conn) readHandshake() (interface{}, error) {
   772		for c.hand.Len() < 4 {
   773			if err := c.in.err; err != nil {
   774				return nil, err
   775			}
   776			if err := c.readRecord(recordTypeHandshake); err != nil {
   777				return nil, err
   778			}
   779		}
   780	
   781		data := c.hand.Bytes()
   782		n := int(data[1])<<16 | int(data[2])<<8 | int(data[3])
   783		if n > maxHandshake {
   784			return nil, c.in.setErrorLocked(c.sendAlert(alertInternalError))
   785		}
   786		for c.hand.Len() < 4+n {
   787			if err := c.in.err; err != nil {
   788				return nil, err
   789			}
   790			if err := c.readRecord(recordTypeHandshake); err != nil {
   791				return nil, err
   792			}
   793		}
   794		data = c.hand.Next(4 + n)
   795		var m handshakeMessage
   796		switch data[0] {
   797		case typeClientHello:
   798			m = new(clientHelloMsg)
   799		case typeServerHello:
   800			m = new(serverHelloMsg)
   801		case typeNewSessionTicket:
   802			m = new(newSessionTicketMsg)
   803		case typeCertificate:
   804			m = new(certificateMsg)
   805		case typeCertificateRequest:
   806			m = &certificateRequestMsg{
   807				hasSignatureAndHash: c.vers >= VersionTLS12,
   808			}
   809		case typeCertificateStatus:
   810			m = new(certificateStatusMsg)
   811		case typeServerKeyExchange:
   812			m = new(serverKeyExchangeMsg)
   813		case typeServerHelloDone:
   814			m = new(serverHelloDoneMsg)
   815		case typeClientKeyExchange:
   816			m = new(clientKeyExchangeMsg)
   817		case typeCertificateVerify:
   818			m = &certificateVerifyMsg{
   819				hasSignatureAndHash: c.vers >= VersionTLS12,
   820			}
   821		case typeNextProtocol:
   822			m = new(nextProtoMsg)
   823		case typeFinished:
   824			m = new(finishedMsg)
   825		default:
   826			return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   827		}
   828	
   829		// The handshake message unmarshallers
   830		// expect to be able to keep references to data,
   831		// so pass in a fresh copy that won't be overwritten.
   832		data = append([]byte(nil), data...)
   833	
   834		if !m.unmarshal(data) {
   835			return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
   836		}
   837		return m, nil
   838	}
   839	
   840	// Write writes data to the connection.
   841	func (c *Conn) Write(b []byte) (int, error) {
   842		if err := c.Handshake(); err != nil {
   843			return 0, err
   844		}
   845	
   846		c.out.Lock()
   847		defer c.out.Unlock()
   848	
   849		if err := c.out.err; err != nil {
   850			return 0, err
   851		}
   852	
   853		if !c.handshakeComplete {
   854			return 0, alertInternalError
   855		}
   856	
   857		// SSL 3.0 and TLS 1.0 are susceptible to a chosen-plaintext
   858		// attack when using block mode ciphers due to predictable IVs.
   859		// This can be prevented by splitting each Application Data
   860		// record into two records, effectively randomizing the IV.
   861		//
   862		// http://www.openssl.org/~bodo/tls-cbc.txt
   863		// https://bugzilla.mozilla.org/show_bug.cgi?id=665814
   864		// http://www.imperialviolet.org/2012/01/15/beastfollowup.html
   865	
   866		var m int
   867		if len(b) > 1 && c.vers <= VersionTLS10 {
   868			if _, ok := c.out.cipher.(cipher.BlockMode); ok {
   869				n, err := c.writeRecord(recordTypeApplicationData, b[:1])
   870				if err != nil {
   871					return n, c.out.setErrorLocked(err)
   872				}
   873				m, b = 1, b[1:]
   874			}
   875		}
   876	
   877		n, err := c.writeRecord(recordTypeApplicationData, b)
   878		return n + m, c.out.setErrorLocked(err)
   879	}
   880	
   881	// Read can be made to time out and return a net.Error with Timeout() == true
   882	// after a fixed time limit; see SetDeadline and SetReadDeadline.
   883	func (c *Conn) Read(b []byte) (n int, err error) {
   884		if err = c.Handshake(); err != nil {
   885			return
   886		}
   887		if len(b) == 0 {
   888			// Put this after Handshake, in case people were calling
   889			// Read(nil) for the side effect of the Handshake.
   890			return
   891		}
   892	
   893		c.in.Lock()
   894		defer c.in.Unlock()
   895	
   896		// Some OpenSSL servers send empty records in order to randomize the
   897		// CBC IV. So this loop ignores a limited number of empty records.
   898		const maxConsecutiveEmptyRecords = 100
   899		for emptyRecordCount := 0; emptyRecordCount <= maxConsecutiveEmptyRecords; emptyRecordCount++ {
   900			for c.input == nil && c.in.err == nil {
   901				if err := c.readRecord(recordTypeApplicationData); err != nil {
   902					// Soft error, like EAGAIN
   903					return 0, err
   904				}
   905			}
   906			if err := c.in.err; err != nil {
   907				return 0, err
   908			}
   909	
   910			n, err = c.input.Read(b)
   911			if c.input.off >= len(c.input.data) {
   912				c.in.freeBlock(c.input)
   913				c.input = nil
   914			}
   915	
   916			// If a close-notify alert is waiting, read it so that
   917			// we can return (n, EOF) instead of (n, nil), to signal
   918			// to the HTTP response reading goroutine that the
   919			// connection is now closed. This eliminates a race
   920			// where the HTTP response reading goroutine would
   921			// otherwise not observe the EOF until its next read,
   922			// by which time a client goroutine might have already
   923			// tried to reuse the HTTP connection for a new
   924			// request.
   925			// See https://codereview.appspot.com/76400046
   926			// and http://golang.org/issue/3514
   927			if ri := c.rawInput; ri != nil &&
   928				n != 0 && err == nil &&
   929				c.input == nil && len(ri.data) > 0 && recordType(ri.data[0]) == recordTypeAlert {
   930				if recErr := c.readRecord(recordTypeApplicationData); recErr != nil {
   931					err = recErr // will be io.EOF on closeNotify
   932				}
   933			}
   934	
   935			if n != 0 || err != nil {
   936				return n, err
   937			}
   938		}
   939	
   940		return 0, io.ErrNoProgress
   941	}
   942	
   943	// Close closes the connection.
   944	func (c *Conn) Close() error {
   945		var alertErr error
   946	
   947		c.handshakeMutex.Lock()
   948		defer c.handshakeMutex.Unlock()
   949		if c.handshakeComplete {
   950			alertErr = c.sendAlert(alertCloseNotify)
   951		}
   952	
   953		if err := c.conn.Close(); err != nil {
   954			return err
   955		}
   956		return alertErr
   957	}
   958	
   959	// Handshake runs the client or server handshake
   960	// protocol if it has not yet been run.
   961	// Most uses of this package need not call Handshake
   962	// explicitly: the first Read or Write will call it automatically.
   963	func (c *Conn) Handshake() error {
   964		c.handshakeMutex.Lock()
   965		defer c.handshakeMutex.Unlock()
   966		if err := c.handshakeErr; err != nil {
   967			return err
   968		}
   969		if c.handshakeComplete {
   970			return nil
   971		}
   972	
   973		if c.isClient {
   974			c.handshakeErr = c.clientHandshake()
   975		} else {
   976			c.handshakeErr = c.serverHandshake()
   977		}
   978		return c.handshakeErr
   979	}
   980	
   981	// ConnectionState returns basic TLS details about the connection.
   982	func (c *Conn) ConnectionState() ConnectionState {
   983		c.handshakeMutex.Lock()
   984		defer c.handshakeMutex.Unlock()
   985	
   986		var state ConnectionState
   987		state.HandshakeComplete = c.handshakeComplete
   988		if c.handshakeComplete {
   989			state.Version = c.vers
   990			state.NegotiatedProtocol = c.clientProtocol
   991			state.DidResume = c.didResume
   992			state.NegotiatedProtocolIsMutual = !c.clientProtocolFallback
   993			state.CipherSuite = c.cipherSuite
   994			state.PeerCertificates = c.peerCertificates
   995			state.VerifiedChains = c.verifiedChains
   996			state.ServerName = c.serverName
   997		}
   998	
   999		return state
  1000	}
  1001	
  1002	// OCSPResponse returns the stapled OCSP response from the TLS server, if
  1003	// any. (Only valid for client connections.)
  1004	func (c *Conn) OCSPResponse() []byte {
  1005		c.handshakeMutex.Lock()
  1006		defer c.handshakeMutex.Unlock()
  1007	
  1008		return c.ocspResponse
  1009	}
  1010	
  1011	// VerifyHostname checks that the peer certificate chain is valid for
  1012	// connecting to host.  If so, it returns nil; if not, it returns an error
  1013	// describing the problem.
  1014	func (c *Conn) VerifyHostname(host string) error {
  1015		c.handshakeMutex.Lock()
  1016		defer c.handshakeMutex.Unlock()
  1017		if !c.isClient {
  1018			return errors.New("tls: VerifyHostname called on TLS server connection")
  1019		}
  1020		if !c.handshakeComplete {
  1021			return errors.New("tls: handshake has not yet been performed")
  1022		}
  1023		return c.peerCertificates[0].VerifyHostname(host)
  1024	}
  1025	

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