asn1: Stricter checks for DER encoded booleans

According to X.690, only 0 and 255 are allowed as values
for encoded booleans. Also added some test for parsing
booleans

R=golang-dev, agl, r
CC=golang-dev
https://golang.org/cl/9692043

src/pkg/encoding/asn1/asn1.go

@@ -47,11 +47,23 @@ func (e SyntaxError) Error() string { return "ASN.1 syntax error: " + e.Msg }
 
 func parseBool(bytes []byte) (ret bool, err error) {
 	if len(bytes) != 1 {
-		err = SyntaxError{"invalid boolean"}
+		err = SyntaxError{"encoding/asn1: invalid boolean"}
 		return
 	}
 
-	return bytes[0] != 0, nil
+	// DER demands that "If the encoding represents the boolean value TRUE,
+	// its single contents octet shall have all eight bits set to one."
+	// Thus only 0 and 255 are valid encoded values.
+	switch bytes[0] {
+	case 0:
+		ret = false
+	case 0xff:
+		ret = true
+	default:
+		err = SyntaxError{"encoding/asn1: invalid boolean"}
+	}
+
+	return
 }
 
 // INTEGER

src/pkg/encoding/asn1/asn1_test.go

@@ -12,6 +12,32 @@ import (
 	"time"
 )
 
+type boolTest struct {
+	in  []byte
+	ok  bool
+	out bool
+}
+
+var boolTestData = []boolTest{
+	{[]byte{0x00}, true, false},
+	{[]byte{0xff}, true, true},
+	{[]byte{0x00, 0x00}, false, false},
+	{[]byte{0xff, 0xff}, false, false},
+	{[]byte{0x01}, false, false},
+}
+
+func TestParseBool(t *testing.T) {
+	for i, test := range boolTestData {
+		ret, err := parseBool(test.in)
+		if (err == nil) != test.ok {
+			t.Errorf("#%d: Incorrect error result (did fail? %v, expected: %v)", i, err == nil, test.ok)
+		}
+		if test.ok && ret != test.out {
+			t.Errorf("#%d: Bad result: %v (expected %v)", i, ret, test.out)
+		}
+	}
+}
+
 type int64Test struct {
 	in  []byte
 	ok  bool
@@ -378,7 +404,7 @@ var unmarshalTestData = []struct {
 	{[]byte{0x30, 0x03, 0x81, 0x01, 0x01}, &TestContextSpecificTags{1}},
 	{[]byte{0x30, 0x08, 0xa1, 0x03, 0x02, 0x01, 0x01, 0x02, 0x01, 0x02}, &TestContextSpecificTags2{1, 2}},
 	{[]byte{0x01, 0x01, 0x00}, newBool(false)},
-	{[]byte{0x01, 0x01, 0x01}, newBool(true)},
+	{[]byte{0x01, 0x01, 0xff}, newBool(true)},
 	{[]byte{0x30, 0x0b, 0x13, 0x03, 0x66, 0x6f, 0x6f, 0x02, 0x01, 0x22, 0x02, 0x01, 0x33}, &TestElementsAfterString{"foo", 0x22, 0x33}},
 	{[]byte{0x30, 0x05, 0x02, 0x03, 0x12, 0x34, 0x56}, &TestBigInt{big.NewInt(0x123456)}},
 }