Do Duplicate Address Detection on permanent IPv6 addresses.

This change adds support for Duplicate Address Detection on IPv6 addresses
as defined by RFC 4862 section 5.4.

Note, this change will not break existing uses of netstack as the default
configuration for the stack options is set in such a way that DAD will not be
performed. See `stack.Options` and `stack.NDPConfigurations` for more details.

Tests: Tests to make sure that the DAD process properly resolves or fails.
That is, tests make sure that DAD resolves only if:
  - No other node is performing DAD for the same address
  - No other node owns the same address
PiperOrigin-RevId: 275189471

1 files changed, 172 insertions, 0 deletions

diff --git a/pkg/tcpip/header/ndp_options.go b/pkg/tcpip/header/ndp_options.go
new file mode 100644
index 000000000..b28bde15b
--- /dev/null
+++ b/pkg/tcpip/header/ndp_options.go
@@ -0,0 +1,172 @@
+// Copyright 2019 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 (
+	"gvisor.dev/gvisor/pkg/tcpip"
+)
+
+const (
+	// NDPTargetLinkLayerAddressOptionType is the type of the Target
+	// Link-Layer Address option, as per RFC 4861 section 4.6.1.
+	NDPTargetLinkLayerAddressOptionType = 2
+
+	// ndpTargetEthernetLinkLayerAddressSize is the size of a Target
+	// Link Layer Option for an Ethernet address.
+	ndpTargetEthernetLinkLayerAddressSize = 8
+
+	// lengthByteUnits is the multiplier factor for the Length field of an
+	// NDP option. That is, the length field for NDP options is in units of
+	// 8 octets, as per RFC 4861 section 4.6.
+	lengthByteUnits = 8
+)
+
+// NDPOptions is a buffer of NDP options as defined by RFC 4861 section 4.6.
+type NDPOptions []byte
+
+// Serialize serializes the provided list of NDP options into o.
+//
+// Note, b must be of sufficient size to hold all the options in s. See
+// NDPOptionsSerializer.Length for details on the getting the total size
+// of a serialized NDPOptionsSerializer.
+//
+// Serialize may panic if b is not of sufficient size to hold all the options
+// in s.
+func (b NDPOptions) Serialize(s NDPOptionsSerializer) int {
+	done := 0
+
+	for _, o := range s {
+		l := paddedLength(o)
+
+		if l == 0 {
+			continue
+		}
+
+		b[0] = o.Type()
+
+		// We know this safe because paddedLength would have returned
+		// 0 if o had an invalid length (> 255 * lengthByteUnits).
+		b[1] = uint8(l / lengthByteUnits)
+
+		// Serialize NDP option body.
+		used := o.serializeInto(b[2:])
+
+		// Zero out remaining (padding) bytes, if any exists.
+		for i := used + 2; i < l; i++ {
+			b[i] = 0
+		}
+
+		b = b[l:]
+		done += l
+	}
+
+	return done
+}
+
+// ndpOption is the set of functions to be implemented by all NDP option types.
+type ndpOption interface {
+	// Type returns the type of this ndpOption.
+	Type() uint8
+
+	// Length returns the length of the body of this ndpOption, in bytes.
+	Length() int
+
+	// serializeInto serializes this ndpOption into the provided byte
+	// buffer.
+	//
+	// Note, the caller MUST provide a byte buffer with size of at least
+	// Length. Implementers of this function may assume that the byte buffer
+	// is of sufficient size. serializeInto MAY panic if the provided byte
+	// buffer is not of sufficient size.
+	//
+	// serializeInto will return the number of bytes that was used to
+	// serialize this ndpOption. Implementers must only use the number of
+	// bytes required to serialize this ndpOption. Callers MAY provide a
+	// larger buffer than required to serialize into.
+	serializeInto([]byte) int
+}
+
+// paddedLength returns the length of o, in bytes, with any padding bytes, if
+// required.
+func paddedLength(o ndpOption) int {
+	l := o.Length()
+
+	if l == 0 {
+		return 0
+	}
+
+	// Length excludes the 2 Type and Length bytes.
+	l += 2
+
+	// Add extra bytes if needed to make sure the option is
+	// lengthByteUnits-byte aligned. We do this by adding lengthByteUnits-1
+	// to l and then stripping off the last few LSBits from l. This will
+	// make sure that l is rounded up to the nearest unit of
+	// lengthByteUnits. This works since lengthByteUnits is a power of 2
+	// (= 8).
+	mask := lengthByteUnits - 1
+	l += mask
+	l &^= mask
+
+	if l/lengthByteUnits > 255 {
+		// Should never happen because an option can only have a max
+		// value of 255 for its Length field, so just return 0 so this
+		// option does not get serialized.
+		//
+		// Returning 0 here will make sure that this option does not get
+		// serialized when NDPOptions.Serialize is called with the
+		// NDPOptionsSerializer that holds this option, effectively
+		// skipping this option during serialization. Also note that
+		// a value of zero for the Length field in an NDP option is
+		// invalid so this is another sign to the caller that this NDP
+		// option is malformed, as per RFC 4861 section 4.6.
+		return 0
+	}
+
+	return l
+}
+
+// NDPOptionsSerializer is a serializer for NDP options.
+type NDPOptionsSerializer []ndpOption
+
+// Length returns the total number of bytes required to serialize.
+func (b NDPOptionsSerializer) Length() int {
+	l := 0
+
+	for _, o := range b {
+		l += paddedLength(o)
+	}
+
+	return l
+}
+
+// NDPTargetLinkLayerAddressOption is the NDP Target Link Layer Option
+// as defined by RFC 4861 section 4.6.1.
+type NDPTargetLinkLayerAddressOption tcpip.LinkAddress
+
+// Type implements ndpOption.Type.
+func (o NDPTargetLinkLayerAddressOption) Type() uint8 {
+	return NDPTargetLinkLayerAddressOptionType
+}
+
+// Length implements ndpOption.Length.
+func (o NDPTargetLinkLayerAddressOption) Length() int {
+	return len(o)
+}
+
+// serializeInto implements ndpOption.serializeInto.
+func (o NDPTargetLinkLayerAddressOption) serializeInto(b []byte) int {
+	return copy(b, o)
+}