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introduce a separate code path for unpacking short header packets

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This commit is contained in:
Marten Seemann 2022-08-27 22:30:09 +03:00
parent ed15a94703
commit 4f3d3b36ac
7 changed files with 390 additions and 245 deletions
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97
packet_unpacker.go
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@ -37,22 +37,25 @@ type unpackedPacket struct {
type packetUnpacker struct {
cs handshake.CryptoSetup
version protocol.VersionNumber
shortHdrConnIDLen int
version protocol.VersionNumber
}
var _ unpacker = &packetUnpacker{}
func newPacketUnpacker(cs handshake.CryptoSetup, version protocol.VersionNumber) unpacker {
func newPacketUnpacker(cs handshake.CryptoSetup, shortHdrConnIDLen int, version protocol.VersionNumber) unpacker {
return &packetUnpacker{
cs: cs,
version: version,
cs: cs,
shortHdrConnIDLen: shortHdrConnIDLen,
version: version,
}
}
// UnpackLongHeader unpacks a Long Header packet.
// If the reserved bits are invalid, the error is wire.ErrInvalidReservedBits.
// If any other error occurred when parsing the header, the error is of type headerParseError.
// If decrypting the payload fails for any reason, the error is the error returned by the AEAD.
func (u *packetUnpacker) Unpack(hdr *wire.Header, rcvTime time.Time, data []byte) (*unpackedPacket, error) {
func (u *packetUnpacker) UnpackLongHeader(hdr *wire.Header, rcvTime time.Time, data []byte) (*unpackedPacket, error) {
var encLevel protocol.EncryptionLevel
var extHdr *wire.ExtendedHeader
var decrypted []byte
@ -89,18 +92,7 @@ func (u *packetUnpacker) Unpack(hdr *wire.Header, rcvTime time.Time, data []byte
return nil, err
}
default:
if hdr.IsLongHeader {
return nil, fmt.Errorf("unknown packet type: %s", hdr.Type)
}
encLevel = protocol.Encryption1RTT
opener, err := u.cs.Get1RTTOpener()
if err != nil {
return nil, err
}
extHdr, decrypted, err = u.unpackShortHeaderPacket(opener, hdr, rcvTime, data)
if err != nil {
return nil, err
}
return nil, fmt.Errorf("unknown packet type: %s", hdr.Type)
}
if len(decrypted) == 0 {
@ -117,8 +109,26 @@ func (u *packetUnpacker) Unpack(hdr *wire.Header, rcvTime time.Time, data []byte
}, nil
}
func (u *packetUnpacker) UnpackShortHeader(rcvTime time.Time, data []byte) (*wire.ShortHeader, []byte, error) {
opener, err := u.cs.Get1RTTOpener()
if err != nil {
return nil, nil, err
}
hdr, decrypted, err := u.unpackShortHeaderPacket(opener, rcvTime, data)
if err != nil {
return nil, nil, err
}
if len(decrypted) == 0 {
return nil, nil, &qerr.TransportError{
ErrorCode: qerr.ProtocolViolation,
ErrorMessage: "empty packet",
}
}
return hdr, decrypted, nil
}
func (u *packetUnpacker) unpackLongHeaderPacket(opener handshake.LongHeaderOpener, hdr *wire.Header, data []byte) (*wire.ExtendedHeader, []byte, error) {
extHdr, parseErr := u.unpackHeader(opener, hdr, data)
extHdr, parseErr := u.unpackLongHeader(opener, hdr, data)
// If the reserved bits are set incorrectly, we still need to continue unpacking.
// This avoids a timing side-channel, which otherwise might allow an attacker
// to gain information about the header encryption.
@ -137,41 +147,58 @@ func (u *packetUnpacker) unpackLongHeaderPacket(opener handshake.LongHeaderOpene
return extHdr, decrypted, nil
}
func (u *packetUnpacker) unpackShortHeaderPacket(
opener handshake.ShortHeaderOpener,
hdr *wire.Header,
rcvTime time.Time,
data []byte,
) (*wire.ExtendedHeader, []byte, error) {
extHdr, parseErr := u.unpackHeader(opener, hdr, data)
func (u *packetUnpacker) unpackShortHeaderPacket(opener handshake.ShortHeaderOpener, rcvTime time.Time, data []byte) (*wire.ShortHeader, []byte, error) {
hdr, parseErr := u.unpackShortHeader(opener, data)
// If the reserved bits are set incorrectly, we still need to continue unpacking.
// This avoids a timing side-channel, which otherwise might allow an attacker
// to gain information about the header encryption.
if parseErr != nil && parseErr != wire.ErrInvalidReservedBits {
return nil, nil, parseErr
return nil, nil, &headerParseError{parseErr}
}
extHdr.PacketNumber = opener.DecodePacketNumber(extHdr.PacketNumber, extHdr.PacketNumberLen)
extHdrLen := extHdr.ParsedLen()
decrypted, err := opener.Open(data[extHdrLen:extHdrLen], data[extHdrLen:], rcvTime, extHdr.PacketNumber, extHdr.KeyPhase, data[:extHdrLen])
hdr.PacketNumber = opener.DecodePacketNumber(hdr.PacketNumber, hdr.PacketNumberLen)
l := hdr.Len()
decrypted, err := opener.Open(data[l:l], data[l:], rcvTime, hdr.PacketNumber, hdr.KeyPhase, data[:l])
if err != nil {
return nil, nil, err
}
if parseErr != nil {
return nil, nil, parseErr
return hdr, decrypted, parseErr
}
func (u *packetUnpacker) unpackShortHeader(hd headerDecryptor, data []byte) (*wire.ShortHeader, error) {
hdrLen := 1 /* first header byte */ + u.shortHdrConnIDLen
if len(data) < hdrLen+4+16 {
return nil, fmt.Errorf("packet too small, expected at least 20 bytes after the header, got %d", len(data)-hdrLen)
}
return extHdr, decrypted, nil
origPNBytes := make([]byte, 4)
copy(origPNBytes, data[hdrLen:hdrLen+4])
// 2. decrypt the header, assuming a 4 byte packet number
hd.DecryptHeader(
data[hdrLen+4:hdrLen+4+16],
&data[0],
data[hdrLen:hdrLen+4],
)
// 3. parse the header (and learn the actual length of the packet number)
hdr, parseErr := wire.ParseShortHeader(data, u.shortHdrConnIDLen)
if parseErr != nil && parseErr != wire.ErrInvalidReservedBits {
return nil, parseErr
}
// 4. if the packet number is shorter than 4 bytes, replace the remaining bytes with the copy we saved earlier
if hdr.PacketNumberLen != protocol.PacketNumberLen4 {
copy(data[hdrLen+int(hdr.PacketNumberLen):hdrLen+4], origPNBytes[int(hdr.PacketNumberLen):])
}
return hdr, parseErr
}
// The error is either nil, a wire.ErrInvalidReservedBits or of type headerParseError.
func (u *packetUnpacker) unpackHeader(hd headerDecryptor, hdr *wire.Header, data []byte) (*wire.ExtendedHeader, error) {
extHdr, err := unpackHeader(hd, hdr, data, u.version)
func (u *packetUnpacker) unpackLongHeader(hd headerDecryptor, hdr *wire.Header, data []byte) (*wire.ExtendedHeader, error) {
extHdr, err := unpackLongHeader(hd, hdr, data, u.version)
if err != nil && err != wire.ErrInvalidReservedBits {
return nil, &headerParseError{err: err}
}
return extHdr, err
}
func unpackHeader(hd headerDecryptor, hdr *wire.Header, data []byte, version protocol.VersionNumber) (*wire.ExtendedHeader, error) {
func unpackLongHeader(hd headerDecryptor, hdr *wire.Header, data []byte, version protocol.VersionNumber) (*wire.ExtendedHeader, error) {
r := bytes.NewReader(data)
hdrLen := hdr.ParsedLen()