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