crypto/tls: check errors from (*Conn).writeRecord

This promotes a connection hang during TLS handshake to a proper error.
This doesn't fully address #14539 because the error reported in that
case is a write-on-socket-not-connected error, which implies that an
earlier error during connection setup is not being checked, but it is
an improvement over the current behaviour.

Updates #14539.

Change-Id: I0571a752d32d5303db48149ab448226868b19495
Reviewed-on: https://go-review.googlesource.com/19990
Reviewed-by: Adam Langley <agl@golang.org>

conn.go

@@ -694,12 +694,14 @@ func (c *Conn) sendAlertLocked(err alert) error {
 		c.tmp[0] = alertLevelError
 	}
 	c.tmp[1] = byte(err)
-	c.writeRecord(recordTypeAlert, c.tmp[0:2])
-	// closeNotify is a special case in that it isn't an error:
-	if err != alertCloseNotify {
-		return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
+
+	_, writeErr := c.writeRecord(recordTypeAlert, c.tmp[0:2])
+	if err == alertCloseNotify {
+		// closeNotify is a special case in that it isn't an error.
+		return writeErr
 	}
-	return nil
+
+	return c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
 }
 
 // sendAlert sends a TLS alert message.
@@ -713,8 +715,11 @@ func (c *Conn) sendAlert(err alert) error {
 // writeRecord writes a TLS record with the given type and payload
 // to the connection and updates the record layer state.
 // c.out.Mutex <= L.
-func (c *Conn) writeRecord(typ recordType, data []byte) (n int, err error) {
+func (c *Conn) writeRecord(typ recordType, data []byte) (int, error) {
 	b := c.out.newBlock()
+	defer c.out.freeBlock(b)
+
+	var n int
 	for len(data) > 0 {
 		m := len(data)
 		if m > maxPlaintext {
@@ -759,34 +764,27 @@ func (c *Conn) writeRecord(typ recordType, data []byte) (n int, err error) {
 			if explicitIVIsSeq {
 				copy(explicitIV, c.out.seq[:])
 			} else {
-				if _, err = io.ReadFull(c.config.rand(), explicitIV); err != nil {
-					break
+				if _, err := io.ReadFull(c.config.rand(), explicitIV); err != nil {
+					return n, err
 				}
 			}
 		}
 		copy(b.data[recordHeaderLen+explicitIVLen:], data)
 		c.out.encrypt(b, explicitIVLen)
-		_, err = c.conn.Write(b.data)
-		if err != nil {
-			break
+		if _, err := c.conn.Write(b.data); err != nil {
+			return n, err
 		}
 		n += m
 		data = data[m:]
 	}
-	c.out.freeBlock(b)
 
 	if typ == recordTypeChangeCipherSpec {
-		err = c.out.changeCipherSpec()
-		if err != nil {
-			// Cannot call sendAlert directly,
-			// because we already hold c.out.Mutex.
-			c.tmp[0] = alertLevelError
-			c.tmp[1] = byte(err.(alert))
-			c.writeRecord(recordTypeAlert, c.tmp[0:2])
-			return n, c.out.setErrorLocked(&net.OpError{Op: "local error", Err: err})
+		if err := c.out.changeCipherSpec(); err != nil {
+			return n, c.sendAlertLocked(err.(alert))
 		}
 	}
-	return
+
+	return n, nil
 }
 
 // readHandshake reads the next handshake message from

handshake_client.go

@@ -138,7 +138,9 @@ NextCipherSuite:
 		}
 	}
 
-	c.writeRecord(recordTypeHandshake, hello.marshal())
+	if _, err := c.writeRecord(recordTypeHandshake, hello.marshal()); err != nil {
+		return err
+	}
 
 	msg, err := c.readHandshake()
 	if err != nil {
@@ -419,7 +421,9 @@ func (hs *clientHandshakeState) doFullHandshake() error {
 			certMsg.certificates = chainToSend.Certificate
 		}
 		hs.finishedHash.Write(certMsg.marshal())
-		c.writeRecord(recordTypeHandshake, certMsg.marshal())
+		if _, err := c.writeRecord(recordTypeHandshake, certMsg.marshal()); err != nil {
+			return err
+		}
 	}
 
 	preMasterSecret, ckx, err := keyAgreement.generateClientKeyExchange(c.config, hs.hello, certs[0])
@@ -429,7 +433,9 @@ func (hs *clientHandshakeState) doFullHandshake() error {
 	}
 	if ckx != nil {
 		hs.finishedHash.Write(ckx.marshal())
-		c.writeRecord(recordTypeHandshake, ckx.marshal())
+		if _, err := c.writeRecord(recordTypeHandshake, ckx.marshal()); err != nil {
+			return err
+		}
 	}
 
 	if chainToSend != nil {
@@ -471,7 +477,9 @@ func (hs *clientHandshakeState) doFullHandshake() error {
 		}
 
 		hs.finishedHash.Write(certVerify.marshal())
-		c.writeRecord(recordTypeHandshake, certVerify.marshal())
+		if _, err := c.writeRecord(recordTypeHandshake, certVerify.marshal()); err != nil {
+			return err
+		}
 	}
 
 	hs.masterSecret = masterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret, hs.hello.random, hs.serverHello.random)
@@ -615,7 +623,9 @@ func (hs *clientHandshakeState) readSessionTicket() error {
 func (hs *clientHandshakeState) sendFinished(out []byte) error {
 	c := hs.c
 
-	c.writeRecord(recordTypeChangeCipherSpec, []byte{1})
+	if _, err := c.writeRecord(recordTypeChangeCipherSpec, []byte{1}); err != nil {
+		return err
+	}
 	if hs.serverHello.nextProtoNeg {
 		nextProto := new(nextProtoMsg)
 		proto, fallback := mutualProtocol(c.config.NextProtos, hs.serverHello.nextProtos)
@@ -624,13 +634,17 @@ func (hs *clientHandshakeState) sendFinished(out []byte) error {
 		c.clientProtocolFallback = fallback
 
 		hs.finishedHash.Write(nextProto.marshal())
-		c.writeRecord(recordTypeHandshake, nextProto.marshal())
+		if _, err := c.writeRecord(recordTypeHandshake, nextProto.marshal()); err != nil {
+			return err
+		}
 	}
 
 	finished := new(finishedMsg)
 	finished.verifyData = hs.finishedHash.clientSum(hs.masterSecret)
 	hs.finishedHash.Write(finished.marshal())
-	c.writeRecord(recordTypeHandshake, finished.marshal())
+	if _, err := c.writeRecord(recordTypeHandshake, finished.marshal()); err != nil {
+		return err
+	}
 	copy(out, finished.verifyData)
 	return nil
 }

handshake_client_test.go

@@ -12,6 +12,7 @@ import (
 	"encoding/base64"
 	"encoding/binary"
 	"encoding/pem"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -725,3 +726,51 @@ func TestServerSelectingUnconfiguredCipherSuite(t *testing.T) {
 		t.Fatalf("Expected error about unconfigured cipher suite but got %q", err)
 	}
 }
+
+// brokenConn wraps a net.Conn and causes all Writes after a certain number to
+// fail with brokenConnErr.
+type brokenConn struct {
+	net.Conn
+
+	// breakAfter is the number of successful writes that will be allowed
+	// before all subsequent writes fail.
+	breakAfter int
+
+	// numWrites is the number of writes that have been done.
+	numWrites int
+}
+
+// brokenConnErr is the error that brokenConn returns once exhausted.
+var brokenConnErr = errors.New("too many writes to brokenConn")
+
+func (b *brokenConn) Write(data []byte) (int, error) {
+	if b.numWrites >= b.breakAfter {
+		return 0, brokenConnErr
+	}
+
+	b.numWrites++
+	return b.Conn.Write(data)
+}
+
+func TestFailedWrite(t *testing.T) {
+	// Test that a write error during the handshake is returned.
+	for _, breakAfter := range []int{0, 1, 2, 3} {
+		c, s := net.Pipe()
+		done := make(chan bool)
+
+		go func() {
+			Server(s, testConfig).Handshake()
+			s.Close()
+			done <- true
+		}()
+
+		brokenC := &brokenConn{Conn: c, breakAfter: breakAfter}
+		err := Client(brokenC, testConfig).Handshake()
+		if err != brokenConnErr {
+			t.Errorf("#%d: expected error from brokenConn but got %q", breakAfter, err)
+		}
+		brokenC.Close()
+
+		<-done
+	}
+}

handshake_server.go

@@ -322,7 +322,9 @@ func (hs *serverHandshakeState) doResumeHandshake() error {
 	hs.finishedHash.discardHandshakeBuffer()
 	hs.finishedHash.Write(hs.clientHello.marshal())
 	hs.finishedHash.Write(hs.hello.marshal())
-	c.writeRecord(recordTypeHandshake, hs.hello.marshal())
+	if _, err := c.writeRecord(recordTypeHandshake, hs.hello.marshal()); err != nil {
+		return err
+	}
 
 	if len(hs.sessionState.certificates) > 0 {
 		if _, err := hs.processCertsFromClient(hs.sessionState.certificates); err != nil {
@@ -354,19 +356,25 @@ func (hs *serverHandshakeState) doFullHandshake() error {
 	}
 	hs.finishedHash.Write(hs.clientHello.marshal())
 	hs.finishedHash.Write(hs.hello.marshal())
-	c.writeRecord(recordTypeHandshake, hs.hello.marshal())
+	if _, err := c.writeRecord(recordTypeHandshake, hs.hello.marshal()); err != nil {
+		return err
+	}
 
 	certMsg := new(certificateMsg)
 	certMsg.certificates = hs.cert.Certificate
 	hs.finishedHash.Write(certMsg.marshal())
-	c.writeRecord(recordTypeHandshake, certMsg.marshal())
+	if _, err := c.writeRecord(recordTypeHandshake, certMsg.marshal()); err != nil {
+		return err
+	}
 
 	if hs.hello.ocspStapling {
 		certStatus := new(certificateStatusMsg)
 		certStatus.statusType = statusTypeOCSP
 		certStatus.response = hs.cert.OCSPStaple
 		hs.finishedHash.Write(certStatus.marshal())
-		c.writeRecord(recordTypeHandshake, certStatus.marshal())
+		if _, err := c.writeRecord(recordTypeHandshake, certStatus.marshal()); err != nil {
+			return err
+		}
 	}
 
 	keyAgreement := hs.suite.ka(c.vers)
@@ -377,7 +385,9 @@ func (hs *serverHandshakeState) doFullHandshake() error {
 	}
 	if skx != nil {
 		hs.finishedHash.Write(skx.marshal())
-		c.writeRecord(recordTypeHandshake, skx.marshal())
+		if _, err := c.writeRecord(recordTypeHandshake, skx.marshal()); err != nil {
+			return err
+		}
 	}
 
 	if config.ClientAuth >= RequestClientCert {
@@ -401,12 +411,16 @@ func (hs *serverHandshakeState) doFullHandshake() error {
 			certReq.certificateAuthorities = config.ClientCAs.Subjects()
 		}
 		hs.finishedHash.Write(certReq.marshal())
-		c.writeRecord(recordTypeHandshake, certReq.marshal())
+		if _, err := c.writeRecord(recordTypeHandshake, certReq.marshal()); err != nil {
+			return err
+		}
 	}
 
 	helloDone := new(serverHelloDoneMsg)
 	hs.finishedHash.Write(helloDone.marshal())
-	c.writeRecord(recordTypeHandshake, helloDone.marshal())
+	if _, err := c.writeRecord(recordTypeHandshake, helloDone.marshal()); err != nil {
+		return err
+	}
 
 	var pub crypto.PublicKey // public key for client auth, if any
 
@@ -632,7 +646,9 @@ func (hs *serverHandshakeState) sendSessionTicket() error {
 	}
 
 	hs.finishedHash.Write(m.marshal())
-	c.writeRecord(recordTypeHandshake, m.marshal())
+	if _, err := c.writeRecord(recordTypeHandshake, m.marshal()); err != nil {
+		return err
+	}
 
 	return nil
 }
@@ -640,12 +656,16 @@ func (hs *serverHandshakeState) sendSessionTicket() error {
 func (hs *serverHandshakeState) sendFinished(out []byte) error {
 	c := hs.c
 
-	c.writeRecord(recordTypeChangeCipherSpec, []byte{1})
+	if _, err := c.writeRecord(recordTypeChangeCipherSpec, []byte{1}); err != nil {
+		return err
+	}
 
 	finished := new(finishedMsg)
 	finished.verifyData = hs.finishedHash.serverSum(hs.masterSecret)
 	hs.finishedHash.Write(finished.marshal())
-	c.writeRecord(recordTypeHandshake, finished.marshal())
+	if _, err := c.writeRecord(recordTypeHandshake, finished.marshal()); err != nil {
+		return err
+	}
 
 	c.cipherSuite = hs.suite.id
 	copy(out, finished.verifyData)

handshake_server_test.go

@@ -80,7 +80,10 @@ func testClientHelloFailure(t *testing.T, serverConfig *Config, m handshakeMessa
 		cli.writeRecord(recordTypeHandshake, m.marshal())
 		c.Close()
 	}()
-	err := Server(s, serverConfig).Handshake()
+	hs := serverHandshakeState{
+		c: Server(s, serverConfig),
+	}
+	_, err := hs.readClientHello()
 	s.Close()
 	if len(expectedSubStr) == 0 {
 		if err != nil && err != io.EOF {