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Copy pathconn.go
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1751 lines (1554 loc) · 53.8 KB
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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-Go file.
// TLS low level connection and record layer
package reality
import (
"bytes"
"context"
"crypto/cipher"
"crypto/subtle"
"crypto/x509"
"errors"
"fmt"
"hash"
"io"
"net"
"sync"
"sync/atomic"
"time"
)
// A Conn represents a secured connection.
// It implements the net.Conn interface.
type Conn struct {
AuthKey []byte
ClientVer [3]byte
ClientTime time.Time
ClientShortId [8]byte
// constant
conn net.Conn
isClient bool
handshakeFn func(context.Context) error // (*Conn).clientHandshake or serverHandshake
quic *quicState // nil for non-QUIC connections
// isHandshakeComplete is true if the connection is currently transferring
// application data (i.e. is not currently processing a handshake).
// isHandshakeComplete is true implies handshakeErr == nil.
isHandshakeComplete atomic.Bool
// 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
extMasterSecret bool
didResume bool // whether this connection was a session resumption
didHRR bool // whether a HelloRetryRequest was sent/received
cipherSuite uint16
curveID CurveID
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
// or sending NewSessionTicket messages.
resumptionSecret []byte
echAccepted bool
// ticketKeys is the set of active session ticket keys for this
// connection. The first one is used to encrypt new tickets and
// all are tried to decrypt tickets.
ticketKeys []ticketKey
// 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 is the negotiated ALPN protocol.
clientProtocol string
// 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
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 indicates whether Close has been call in the low bit.
// the rest of the bits are the number of goroutines in Conn.Write.
activeCall atomic.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 [Conn.Read] and [Conn.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 [Conn.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 [Conn.Write] will not time out.
// After a [Conn.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)
}
// NetConn returns the underlying connection that is wrapped by c.
// Note that writing to or reading from this connection directly will corrupt the
// TLS session.
func (c *Conn) NetConn() net.Conn {
return c.conn
}
// A halfConn represents one direction of the record layer
// connection, either sending or receiving.
type halfConn struct {
handshakeLen [7]int
handshakeBuf []byte
sync.Mutex
err error // first permanent error
version uint16 // protocol version
cipher any // cipher algorithm
mac hash.Hash
seq [8]byte // 64-bit sequence number
scratchBuf [13]byte // to avoid allocs; interface method args escape
nextCipher any // next encryption state
nextMac hash.Hash // next MAC algorithm
level QUICEncryptionLevel // current QUIC encryption level
trafficSecret []byte // current TLS 1.3 traffic secret
}
type permanentError struct {
err net.Error
}
func (e *permanentError) Error() string { return e.err.Error() }
func (e *permanentError) Unwrap() error { return e.err }
func (e *permanentError) Timeout() bool { return e.err.Timeout() }
func (e *permanentError) Temporary() bool { return false }
func (hc *halfConn) setErrorLocked(err error) error {
if e, ok := err.(net.Error); ok {
hc.err = &permanentError{err: e}
} else {
hc.err = err
}
return hc.err
}
// prepareCipherSpec sets the encryption and MAC states
// that a subsequent changeCipherSpec will use.
func (hc *halfConn) prepareCipherSpec(version uint16, cipher any, mac hash.Hash) {
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, level QUICEncryptionLevel, secret []byte) {
hc.trafficSecret = secret
hc.level = level
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
}
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:]
var additionalData []byte
if hc.version == VersionTLS13 {
additionalData = record[:recordHeaderLen]
} else {
additionalData = append(hc.scratchBuf[:0], hc.seq[:]...)
additionalData = append(additionalData, record[:3]...)
n := len(payload) - c.Overhead()
additionalData = append(additionalData, byte(n>>8), 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.
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 := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], 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 must already contain 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 similarly small block size
// (see the Sweet32 attack).
copy(explicitNonce, hc.seq[:])
} else {
if _, err := io.ReadFull(rand, explicitNonce); err != nil {
return nil, err
}
}
}
var dst []byte
switch c := hc.cipher.(type) {
case cipher.Stream:
mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
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])
padding := 0
if recordType(record[0]) == recordTypeHandshake && hc.handshakeLen[1] != 0 {
switch payload[0] {
case typeEncryptedExtensions:
padding = hc.handshakeLen[2]
hc.handshakeLen[2] = 0
case typeCertificate:
padding = hc.handshakeLen[3]
hc.handshakeLen[3] = 0
case typeCertificateVerify:
padding = hc.handshakeLen[4]
hc.handshakeLen[4] = 0
case typeFinished:
padding = hc.handshakeLen[5]
hc.handshakeLen[5] = 0
case typeNewSessionTicket:
padding = hc.handshakeLen[6]
hc.handshakeLen[6] = 0
record[5] = byte(recordTypeApplicationData)
record[6] = 0
}
padding -= len(record) + c.Overhead()
if padding < 0 {
return nil, fmt.Errorf("payload[0]: %v, padding: %v", payload[0], padding)
}
record = append(record, empty[:padding]...)
}
record[0] = byte(recordTypeApplicationData)
n := len(record) + c.Overhead() - recordHeaderLen
record[3] = byte(n >> 8)
record[4] = byte(n)
record = c.Seal(record[:recordHeaderLen],
nonce, record[recordHeaderLen:], record[:recordHeaderLen])
} else {
additionalData := append(hc.scratchBuf[:0], hc.seq[:]...)
additionalData = append(additionalData, record[:recordHeaderLen]...)
record = c.Seal(record, nonce, payload, additionalData)
}
case cbcMode:
mac := tls10MAC(hc.mac, hc.scratchBuf[:0], hc.seq[:], record[:recordHeaderLen], payload, nil)
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.isHandshakeComplete.Load()
// 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)
if c.quic != nil {
return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with QUIC transport"))
}
// 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])
expectedVers := c.vers
if expectedVers == VersionTLS13 {
// All TLS 1.3 records are expected to have 0x0303 (1.2) after
// the initial hello (RFC 8446 Section 5.1).
expectedVers = VersionTLS12
}
n := int(hdr[3])<<8 | int(hdr[4])
if c.haveVers && vers != expectedVers {
c.sendAlert(alertProtocolVersion)
msg := fmt.Sprintf("received record with version %x when expecting version %x", vers, expectedVers)
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 c.quic != nil {
return c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
}
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 {
// TLS 1.3 removed warning-level alerts except for alertUserCanceled
// (RFC 8446, § 6.1). Since at least one major implementation
// (https://bugs.openjdk.org/browse/JDK-8323517) misuses this alert,
// many TLS stacks now ignore it outright when seen in a TLS 1.3
// handshake (e.g. BoringSSL, NSS, Rustls).
if alert(data[1]) == alertUserCanceled {
// Like TLS 1.2 alertLevelWarning alerts, we drop the record and retry.
return c.retryReadRecord(expectChangeCipherSpec)
}
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 && !handshakeComplete {
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 recurs 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
}
// sendAlertLocked sends a TLS alert message.
func (c *Conn) sendAlertLocked(err alert) error {
if c.quic != nil {
return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
}
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
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