1 files changed, 344 insertions, 0 deletions
diff --git a/pkg/tcpip/header/ipv6_extension_headers.go b/pkg/tcpip/header/ipv6_extension_headers.go
new file mode 100755
index 000000000..b8866d4d2
--- /dev/null
+++ b/pkg/tcpip/header/ipv6_extension_headers.go
@@ -0,0 +1,344 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package header
+
+import (
+	"bufio"
+	"encoding/binary"
+	"fmt"
+	"io"
+
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+)
+
+// IPv6ExtensionHeaderIdentifier is an IPv6 extension header identifier.
+type IPv6ExtensionHeaderIdentifier uint8
+
+const (
+	// IPv6RoutingExtHdrIdentifier is the header identifier of a Routing extension
+	// header, as per RFC 8200 section 4.4.
+	IPv6RoutingExtHdrIdentifier IPv6ExtensionHeaderIdentifier = 43
+
+	// IPv6FragmentExtHdrIdentifier is the header identifier of a Fragment
+	// extension header, as per RFC 8200 section 4.5.
+	IPv6FragmentExtHdrIdentifier IPv6ExtensionHeaderIdentifier = 44
+
+	// IPv6NoNextHeaderIdentifier is the header identifier used to signify the end
+	// of an IPv6 payload, as per RFC 8200 section 4.7.
+	IPv6NoNextHeaderIdentifier IPv6ExtensionHeaderIdentifier = 59
+)
+
+const (
+	// ipv6RoutingExtHdrSegmentsLeftIdx is the index to the Segments Left field
+	// within an IPv6RoutingExtHdr.
+	ipv6RoutingExtHdrSegmentsLeftIdx = 1
+
+	// ipv6FragmentExtHdrFragmentOffsetOffset is the offset to the start of the
+	// Fragment Offset field within an IPv6FragmentExtHdr.
+	ipv6FragmentExtHdrFragmentOffsetOffset = 0
+
+	// ipv6FragmentExtHdrFragmentOffsetShift is the least significant bits to
+	// discard from the Fragment Offset.
+	ipv6FragmentExtHdrFragmentOffsetShift = 3
+
+	// ipv6FragmentExtHdrFlagsIdx is the index to the flags field within an
+	// IPv6FragmentExtHdr.
+	ipv6FragmentExtHdrFlagsIdx = 1
+
+	// ipv6FragmentExtHdrMFlagMask is the mask of the More (M) flag within the
+	// flags field of an IPv6FragmentExtHdr.
+	ipv6FragmentExtHdrMFlagMask = 1
+
+	// ipv6FragmentExtHdrIdentificationOffset is the offset to the Identification
+	// field within an IPv6FragmentExtHdr.
+	ipv6FragmentExtHdrIdentificationOffset = 2
+
+	// ipv6ExtHdrLenBytesPerUnit is the unit size of an extension header's length
+	// field. That is, given a Length field of 2, the extension header expects
+	// 16 bytes following the first 8 bytes (see ipv6ExtHdrLenBytesExcluded for
+	// details about the first 8 bytes' exclusion from the Length field).
+	ipv6ExtHdrLenBytesPerUnit = 8
+
+	// ipv6ExtHdrLenBytesExcluded is the number of bytes excluded from an
+	// extension header's Length field following the Length field.
+	//
+	// The Length field excludes the first 8 bytes, but the Next Header and Length
+	// field take up the first 2 of the 8 bytes so we expect (at minimum) 6 bytes
+	// after the Length field.
+	//
+	// This ensures that every extension header is at least 8 bytes.
+	ipv6ExtHdrLenBytesExcluded = 6
+
+	// IPv6FragmentExtHdrFragmentOffsetBytesPerUnit is the unit size of a Fragment
+	// extension header's Fragment Offset field. That is, given a Fragment Offset
+	// of 2, the extension header is indiciating that the fragment's payload
+	// starts at the 16th byte in the reassembled packet.
+	IPv6FragmentExtHdrFragmentOffsetBytesPerUnit = 8
+)
+
+// IPv6PayloadHeader is implemented by the various headers that can be found
+// in an IPv6 payload.
+//
+// These headers include IPv6 extension headers or upper layer data.
+type IPv6PayloadHeader interface {
+	isIPv6PayloadHeader()
+}
+
+// IPv6RawPayloadHeader the remainder of an IPv6 payload after an iterator
+// encounters a Next Header field it does not recognize as an IPv6 extension
+// header.
+type IPv6RawPayloadHeader struct {
+	Identifier IPv6ExtensionHeaderIdentifier
+	Buf        buffer.VectorisedView
+}
+
+// isIPv6PayloadHeader implements IPv6PayloadHeader.isIPv6PayloadHeader.
+func (IPv6RawPayloadHeader) isIPv6PayloadHeader() {}
+
+// IPv6RoutingExtHdr is a buffer holding the Routing extension header specific
+// data as outlined in RFC 8200 section 4.4.
+type IPv6RoutingExtHdr []byte
+
+// isIPv6PayloadHeader implements IPv6PayloadHeader.isIPv6PayloadHeader.
+func (IPv6RoutingExtHdr) isIPv6PayloadHeader() {}
+
+// SegmentsLeft returns the Segments Left field.
+func (b IPv6RoutingExtHdr) SegmentsLeft() uint8 {
+	return b[ipv6RoutingExtHdrSegmentsLeftIdx]
+}
+
+// IPv6FragmentExtHdr is a buffer holding the Fragment extension header specific
+// data as outlined in RFC 8200 section 4.5.
+//
+// Note, the buffer does not include the Next Header and Reserved fields.
+type IPv6FragmentExtHdr [6]byte
+
+// isIPv6PayloadHeader implements IPv6PayloadHeader.isIPv6PayloadHeader.
+func (IPv6FragmentExtHdr) isIPv6PayloadHeader() {}
+
+// FragmentOffset returns the Fragment Offset field.
+//
+// This value indicates where the buffer following the Fragment extension header
+// starts in the target (reassembled) packet.
+func (b IPv6FragmentExtHdr) FragmentOffset() uint16 {
+	return binary.BigEndian.Uint16(b[ipv6FragmentExtHdrFragmentOffsetOffset:]) >> ipv6FragmentExtHdrFragmentOffsetShift
+}
+
+// More returns the More (M) flag.
+//
+// This indicates whether any fragments are expected to succeed b.
+func (b IPv6FragmentExtHdr) More() bool {
+	return b[ipv6FragmentExtHdrFlagsIdx]&ipv6FragmentExtHdrMFlagMask != 0
+}
+
+// ID returns the Identification field.
+//
+// This value is used to uniquely identify the packet, between a
+// souce and destination.
+func (b IPv6FragmentExtHdr) ID() uint32 {
+	return binary.BigEndian.Uint32(b[ipv6FragmentExtHdrIdentificationOffset:])
+}
+
+// IPv6PayloadIterator is an iterator over the contents of an IPv6 payload.
+//
+// The IPv6 payload may contain IPv6 extension headers before any upper layer
+// data.
+//
+// Note, between when an IPv6PayloadIterator is obtained and last used, no
+// changes to the payload may happen. Doing so may cause undefined and
+// unexpected behaviour. It is fine to obtain an IPv6PayloadIterator, iterate
+// over the first few headers then modify the backing payload so long as the
+// IPv6PayloadIterator obtained before modification is no longer used.
+type IPv6PayloadIterator struct {
+	// The identifier of the next header to parse.
+	nextHdrIdentifier IPv6ExtensionHeaderIdentifier
+
+	// reader is an io.Reader over payload.
+	reader  bufio.Reader
+	payload buffer.VectorisedView
+
+	// Indicates to the iterator that it should return the remaining payload as a
+	// raw payload on the next call to Next.
+	forceRaw bool
+}
+
+// MakeIPv6PayloadIterator returns an iterator over the IPv6 payload containing
+// extension headers, or a raw payload if the payload cannot be parsed.
+func MakeIPv6PayloadIterator(nextHdrIdentifier IPv6ExtensionHeaderIdentifier, payload buffer.VectorisedView, check bool) (IPv6PayloadIterator, error) {
+	readers := payload.Readers()
+	readerPs := make([]io.Reader, 0, len(readers))
+	for i := range readers {
+		readerPs = append(readerPs, &readers[i])
+	}
+
+	// We need a buffer of size 1 for calls to bufio.Reader.ReadByte.
+	reader := *bufio.NewReaderSize(io.MultiReader(readerPs...), 1)
+
+	it := IPv6PayloadIterator{
+		nextHdrIdentifier: nextHdrIdentifier,
+		payload:           payload.Clone(nil),
+		reader:            reader,
+	}
+
+	var err error
+
+	if check {
+		for {
+			var done bool
+			if _, done, err = it.Next(); err != nil || done {
+				break
+			}
+		}
+
+		// Reset it (and its underlying readers) before returning it.
+		for i := range readers {
+			readers[i].Seek(0, io.SeekStart)
+		}
+		reader.Reset(io.MultiReader(readerPs...))
+		it = IPv6PayloadIterator{
+			nextHdrIdentifier: nextHdrIdentifier,
+			payload:           payload.Clone(nil),
+			reader:            reader,
+		}
+	}
+
+	return it, err
+}
+
+// AsRawHeader returns the remaining payload of i as a raw header and
+// completes the iterator.
+//
+// Calls to Next after calling AsRawHeader on i will indicate that the
+// iterator is done.
+func (i *IPv6PayloadIterator) AsRawHeader() IPv6RawPayloadHeader {
+	buf := i.payload
+	identifier := i.nextHdrIdentifier
+
+	// Mark i as done.
+	*i = IPv6PayloadIterator{
+		nextHdrIdentifier: IPv6NoNextHeaderIdentifier,
+	}
+
+	return IPv6RawPayloadHeader{Identifier: identifier, Buf: buf}
+}
+
+// Next returns the next item in the payload.
+//
+// If the next item is not a known IPv6 extension header, IPv6RawPayloadHeader
+// will be returned with the remaining bytes and next header identifier.
+//
+// The return is of the format (header, done, error). done will be true when
+// Next is unable to return anything because the iterator has reached the end of
+// the payload, or an error occured.
+func (i *IPv6PayloadIterator) Next() (IPv6PayloadHeader, bool, error) {
+	// We could be forced to return i as a raw header when the previous header was
+	// a fragment extension header as the data following the fragment extension
+	// header may not be complete.
+	if i.forceRaw {
+		return i.AsRawHeader(), false, nil
+	}
+
+	// Is the header we are parsing a known extension header?
+	switch i.nextHdrIdentifier {
+	case IPv6RoutingExtHdrIdentifier:
+		nextHdrIdentifier, bytes, err := i.nextHeaderData(false /* fragmentHdr */, nil)
+		if err != nil {
+			return nil, true, err
+		}
+
+		i.nextHdrIdentifier = nextHdrIdentifier
+		return IPv6RoutingExtHdr(bytes), false, nil
+	case IPv6FragmentExtHdrIdentifier:
+		var data [6]byte
+		// We ignore the returned bytes becauase we know the fragment extension
+		// header specific data will fit in data.
+		nextHdrIdentifier, _, err := i.nextHeaderData(true /* fragmentHdr */, data[:])
+		if err != nil {
+			return nil, true, err
+		}
+
+		fragmentExtHdr := IPv6FragmentExtHdr(data)
+
+		// If the packet is a fragmented packet, do not attempt to parse
+		// anything after the fragment extension header as the data following
+		// the extension header may not be complete.
+		if fragmentExtHdr.More() || fragmentExtHdr.FragmentOffset() != 0 {
+			i.forceRaw = true
+		}
+
+		i.nextHdrIdentifier = nextHdrIdentifier
+		return fragmentExtHdr, false, nil
+	case IPv6NoNextHeaderIdentifier:
+		// This indicates the end of the IPv6 payload.
+		return nil, true, nil
+
+	default:
+		// The header we are parsing is not a known extension header. Return the
+		// raw payload.
+		return i.AsRawHeader(), false, nil
+	}
+}
+
+// nextHeaderData returns the extension header's Next Header field and raw data.
+//
+// fragmentHdr indicates that the extension header being parsed is the Fragment
+// extension header so the Length field should be ignored as it is Reserved
+// for the Fragment extension header.
+//
+// If bytes is not nil, extension header specific data will be read into bytes
+// if it has enough capacity. If bytes is provided but does not have enough
+// capacity for the data, nextHeaderData will panic.
+func (i *IPv6PayloadIterator) nextHeaderData(fragmentHdr bool, bytes []byte) (IPv6ExtensionHeaderIdentifier, []byte, error) {
+	// We ignore the number of bytes read because we know we will only ever read
+	// at max 1 bytes since rune has a length of 1. If we read 0 bytes, the Read
+	// would return io.EOF to indicate that io.Reader has reached the end of the
+	// payload.
+	nextHdrIdentifier, err := i.reader.ReadByte()
+	i.payload.TrimFront(1)
+	if err != nil {
+		return 0, nil, fmt.Errorf("error when reading the Next Header field for extension header with id = %d: %w", i.nextHdrIdentifier, err)
+	}
+
+	var length uint8
+	length, err = i.reader.ReadByte()
+	i.payload.TrimFront(1)
+	if err != nil {
+		var ret error
+		if fragmentHdr {
+			ret = fmt.Errorf("error when reading the Length field for extension header with id = %d: %w", i.nextHdrIdentifier, err)
+		} else {
+			ret = fmt.Errorf("error when reading the Reserved field for extension header with id = %d: %w", i.nextHdrIdentifier, err)
+		}
+		return 0, nil, ret
+	}
+	if fragmentHdr {
+		length = 0
+	}
+
+	bytesLen := int(length)*ipv6ExtHdrLenBytesPerUnit + ipv6ExtHdrLenBytesExcluded
+	if bytes == nil {
+		bytes = make([]byte, bytesLen)
+	} else if n := len(bytes); n < bytesLen {
+		panic(fmt.Sprintf("bytes only has space for %d bytes but need space for %d bytes (length = %d) for extension header with id = %d", n, bytesLen, length, i.nextHdrIdentifier))
+	}
+
+	n, err := io.ReadFull(&i.reader, bytes)
+	i.payload.TrimFront(n)
+	if err != nil {
+		return 0, nil, fmt.Errorf("read %d out of %d extension header data bytes (length = %d) for header with id = %d: %w", n, bytesLen, length, i.nextHdrIdentifier, err)
+	}
+
+	return IPv6ExtensionHeaderIdentifier(nextHdrIdentifier), bytes, nil
+}