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fix timing side channel when reading headers with invalid reserved bits

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This commit is contained in:
Marten Seemann 2019-01-28 11:10:50 +09:00
parent 4fe0f6752c
commit 7b9b711a77
4 changed files with 105 additions and 26 deletions
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32
packet_unpacker.go
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@ -91,28 +91,40 @@ func (u *packetUnpacker) Unpack(hdr *wire.Header, data []byte) (*unpackedPacket,
}
func (u *packetUnpacker) unpackLongHeaderPacket(opener handshake.LongHeaderOpener, hdr *wire.Header, data []byte) (*wire.ExtendedHeader, []byte, error) {
extHdr, err := u.unpack(opener, hdr, data)
if err != nil {
return nil, nil, err
extHdr, parseErr := u.unpack(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.
if parseErr != nil && parseErr != wire.ErrInvalidReservedBits {
return nil, nil, fmt.Errorf("error parsing extended header: %s", parseErr)
}
extHdrLen := extHdr.GetLength(u.version)
decrypted, err := opener.Open(data[extHdrLen:extHdrLen], data[extHdrLen:], extHdr.PacketNumber, data[:extHdrLen])
if err != nil {
return nil, nil, err
}
if parseErr != nil {
return nil, nil, parseErr
}
return extHdr, decrypted, nil
}
func (u *packetUnpacker) unpackShortHeaderPacket(opener handshake.ShortHeaderOpener, hdr *wire.Header, data []byte) (*wire.ExtendedHeader, []byte, error) {
extHdr, err := u.unpack(opener, hdr, data)
if err != nil {
return nil, nil, err
extHdr, parseErr := u.unpack(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.
if parseErr != nil && parseErr != wire.ErrInvalidReservedBits {
return nil, nil, parseErr
}
extHdrLen := extHdr.GetLength(u.version)
decrypted, err := opener.Open(data[extHdrLen:extHdrLen], data[extHdrLen:], extHdr.PacketNumber, extHdr.KeyPhase, data[:extHdrLen])
if err != nil {
return nil, nil, err
}
if parseErr != nil {
return nil, nil, parseErr
}
return extHdr, decrypted, nil
}
@ -134,9 +146,9 @@ func (u *packetUnpacker) unpack(hd headerDecryptor, hdr *wire.Header, data []byt
data[hdrLen:hdrLen+4],
)
// 3. parse the header (and learn the actual length of the packet number)
extHdr, err := hdr.ParseExtended(r, u.version)
if err != nil {
return nil, fmt.Errorf("error parsing extended header: %s", err)
extHdr, parseErr := hdr.ParseExtended(r, u.version)
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 extHdr.PacketNumberLen != protocol.PacketNumberLen4 {
@ -148,5 +160,5 @@ func (u *packetUnpacker) unpack(hd headerDecryptor, hdr *wire.Header, data []byt
u.largestRcvdPacketNumber,
extHdr.PacketNumber,
)
return extHdr, nil
return extHdr, parseErr
}