exp/ssh: handle versions with just '\n'

djm recommend that we do this because OpenSSL was only fixed in 2008:
http://anoncvs.mindrot.org/index.cgi/openssh/sshd.c?revision=1.380&view=markup

R=dave, jonathan.mark.pittman
CC=golang-dev
https://golang.org/cl/5555044

src/pkg/exp/ssh/transport.go

@@ -339,7 +339,7 @@ const maxVersionStringBytes = 1024
 // Read version string as specified by RFC 4253, section 4.2.
 func readVersion(r io.Reader) ([]byte, error) {
 	versionString := make([]byte, 0, 64)
-	var ok, seenCR bool
+	var ok bool
 	var buf [1]byte
 forEachByte:
 	for len(versionString) < maxVersionStringBytes {
@@ -347,27 +347,22 @@ forEachByte:
 		if err != nil {
 			return nil, err
 		}
-		b := buf[0]
-
-		if !seenCR {
-			if b == '\r' {
-				seenCR = true
-			}
-		} else {
-			if b == '\n' {
-				ok = true
-				break forEachByte
-			} else {
-				seenCR = false
-			}
+		// The RFC says that the version should be terminated with \r\n
+		// but several SSH servers actually only send a \n.
+		if buf[0] == '\n' {
+			ok = true
+			break forEachByte
 		}
-		versionString = append(versionString, b)
+		versionString = append(versionString, buf[0])
 	}
 
 	if !ok {
-		return nil, errors.New("failed to read version string")
+		return nil, errors.New("ssh: failed to read version string")
 	}
 
-	// We need to remove the CR from versionString
-	return versionString[:len(versionString)-1], nil
+	// There might be a '\r' on the end which we should remove.
+	if len(versionString) > 0 && versionString[len(versionString)-1] == '\r' {
+		versionString = versionString[:len(versionString)-1]
+	}
+	return versionString, nil
 }

src/pkg/exp/ssh/transport_test.go

@@ -11,7 +11,7 @@ import (
 )
 
 func TestReadVersion(t *testing.T) {
-	buf := []byte(serverVersion)
+	buf := serverVersion
 	result, err := readVersion(bufio.NewReader(bytes.NewBuffer(buf)))
 	if err != nil {
 		t.Errorf("readVersion didn't read version correctly: %s", err)
@@ -21,6 +21,20 @@ func TestReadVersion(t *testing.T) {
 	}
 }
 
+func TestReadVersionWithJustLF(t *testing.T) {
+	var buf []byte
+	buf = append(buf, serverVersion...)
+	buf = buf[:len(buf)-1]
+	buf[len(buf)-1] = '\n'
+	result, err := readVersion(bufio.NewReader(bytes.NewBuffer(buf)))
+	if err != nil {
+		t.Error("readVersion failed to handle just a \n")
+	}
+	if !bytes.Equal(buf[:len(buf)-1], result) {
+		t.Errorf("version read did not match expected: got %x, want %x", result, buf[:len(buf)-1])
+	}
+}
+
 func TestReadVersionTooLong(t *testing.T) {
 	buf := make([]byte, maxVersionStringBytes+1)
 	if _, err := readVersion(bufio.NewReader(bytes.NewBuffer(buf))); err == nil {
@@ -29,7 +43,7 @@ func TestReadVersionTooLong(t *testing.T) {
 }
 
 func TestReadVersionWithoutCRLF(t *testing.T) {
-	buf := []byte(serverVersion)
+	buf := serverVersion
 	buf = buf[:len(buf)-1]
 	if _, err := readVersion(bufio.NewReader(bytes.NewBuffer(buf))); err == nil {
 		t.Error("readVersion did not notice \\n was missing")