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smx509: better handling of weird encodings #316

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Sun Yimin 2025-03-14 08:44:52 +08:00 committed by GitHub
parent c32a9849f8
commit e79aab4935
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GPG Key ID: B5690EEEBB952194
2 changed files with 59 additions and 4 deletions
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35
smx509/parser.go
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@ -58,7 +58,21 @@ func isPrintable(b byte) bool {
func parseASN1String(tag cryptobyte_asn1.Tag, value []byte) (string, error) {
switch tag {
case cryptobyte_asn1.T61String:
return string(value), nil
// T.61 is a defunct ITU 8-bit character encoding which preceded Unicode.
// T.61 uses a code page layout that _almost_ exactly maps to the code
// page layout of the ISO 8859-1 (Latin-1) character encoding, with the
// exception that a number of characters in Latin-1 are not present
// in T.61.
//
// Instead of mapping which characters are present in Latin-1 but not T.61,
// we just treat these strings as being encoded using Latin-1. This matches
// what most of the world does, including BoringSSL.
buf := make([]byte, 0, len(value))
for _, v := range value {
// All the 1-byte UTF-8 runes map 1-1 with Latin-1.
buf = utf8.AppendRune(buf, rune(v))
}
return string(buf), nil
case cryptobyte_asn1.PrintableString:
for _, b := range value {
if !isPrintable(b) {
@ -72,6 +86,14 @@ func parseASN1String(tag cryptobyte_asn1.Tag, value []byte) (string, error) {
}
return string(value), nil
case cryptobyte_asn1.Tag(asn1.TagBMPString):
// BMPString uses the defunct UCS-2 16-bit character encoding, which
// covers the Basic Multilingual Plane (BMP). UTF-16 was an extension of
// UCS-2, containing all of the same code points, but also including
// multi-code point characters (by using surrogate code points). We can
// treat a UCS-2 encoded string as a UTF-16 encoded string, as long as
// we reject out the UTF-16 specific code points. This matches the
// BoringSSL behavior.
if len(value)%2 != 0 {
return "", errors.New("invalid BMPString")
}
@ -83,7 +105,16 @@ func parseASN1String(tag cryptobyte_asn1.Tag, value []byte) (string, error) {
s := make([]uint16, 0, len(value)/2)
for len(value) > 0 {
s = append(s, uint16(value[0])<<8+uint16(value[1]))
point := uint16(value[0])<<8 + uint16(value[1])
// Reject UTF-16 code points that are permanently reserved
// noncharacters (0xfffe, 0xffff, and 0xfdd0-0xfdef) and surrogates
// (0xd800-0xdfff).
if point == 0xfffe || point == 0xffff ||
(point >= 0xfdd0 && point <= 0xfdef) ||
(point >= 0xd800 && point <= 0xdfff) {
return "", errors.New("invalid BMPString")
}
s = append(s, point)
value = value[2:]
}

28
smx509/parser_test.go
View File

@ -19,8 +19,8 @@ func TestParseASN1String(t *testing.T) {
{
name: "T61String",
tag: cryptobyte_asn1.T61String,
value: []byte{80, 81, 82},
expected: string("PQR"),
value: []byte{0xbf, 0x61, 0x3f},
expected: string("¿a?"),
},
{
name: "PrintableString",
@ -58,6 +58,30 @@ func TestParseASN1String(t *testing.T) {
value: []byte{255},
expectedErr: "invalid BMPString",
},
{
name: "BMPString (invalid surrogate)",
tag: cryptobyte_asn1.Tag(asn1.TagBMPString),
value: []byte{80, 81, 216, 1},
expectedErr: "invalid BMPString",
},
{
name: "BMPString (invalid noncharacter 0xfdd1)",
tag: cryptobyte_asn1.Tag(asn1.TagBMPString),
value: []byte{80, 81, 253, 209},
expectedErr: "invalid BMPString",
},
{
name: "BMPString (invalid noncharacter 0xffff)",
tag: cryptobyte_asn1.Tag(asn1.TagBMPString),
value: []byte{80, 81, 255, 255},
expectedErr: "invalid BMPString",
},
{
name: "BMPString (invalid noncharacter 0xfffe)",
tag: cryptobyte_asn1.Tag(asn1.TagBMPString),
value: []byte{80, 81, 255, 254},
expectedErr: "invalid BMPString",
},
{
name: "IA5String",
tag: cryptobyte_asn1.IA5String,