Do IPv6 Stateless Address Auto-Configuration (SLAAC)

This change allows the netstack to do SLAAC as outlined by RFC 4862 section 5.5.

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 SLAAC
will not be performed. See `stack.Options` and `stack.NDPConfigurations` for
more details.

This change reuses 1 option and introduces a new one that is required to take
advantage of SLAAC, all available under NDPConfigurations:
- HandleRAs: Whether or not NDP RAs are processes
- AutoGenGlobalAddresses: Whether or not SLAAC is performed.

Also note, this change does not deprecate SLAAC generated addresses after the
preferred lifetime. That will come in a later change (b/143713887). Currently,
only the valid lifetime is honoured.

Tests: Unittest to make sure that SLAAC generates and adds addresses only when
configured to do so. Tests also makes sure that conflicts with static addresses
do not modify the static address.
PiperOrigin-RevId: 284265317

2 files changed, 43 insertions, 15 deletions

diff --git a/pkg/tcpip/header/ipv6.go b/pkg/tcpip/header/ipv6.go
index 0caa51c1e..5275b34d4 100644
--- a/pkg/tcpip/header/ipv6.go
+++ b/pkg/tcpip/header/ipv6.go
@@ -90,6 +90,18 @@ const (
 	// IPv6Any is the non-routable IPv6 "any" meta address. It is also
 	// known as the unspecified address.
 	IPv6Any tcpip.Address = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
+
+	// IIDSize is the size of an interface identifier (IID), in bytes, as
+	// defined by RFC 4291 section 2.5.1.
+	IIDSize = 8
+
+	// IIDOffsetInIPv6Address is the offset, in bytes, from the start
+	// of an IPv6 address to the beginning of the interface identifier
+	// (IID) for auto-generated addresses. That is, all bytes before
+	// the IIDOffsetInIPv6Address-th byte are the prefix bytes, and all
+	// bytes including and after the IIDOffsetInIPv6Address-th byte are
+	// for the IID.
+	IIDOffsetInIPv6Address = 8
 )
 
 // IPv6EmptySubnet is the empty IPv6 subnet. It may also be known as the
@@ -266,6 +278,28 @@ func SolicitedNodeAddr(addr tcpip.Address) tcpip.Address {
 	return solicitedNodeMulticastPrefix + addr[len(addr)-3:]
 }
 
+// EthernetAdddressToEUI64IntoBuf populates buf with a EUI-64 from a 48-bit
+// Ethernet/MAC address.
+//
+// buf MUST be at least 8 bytes.
+func EthernetAdddressToEUI64IntoBuf(linkAddr tcpip.LinkAddress, buf []byte) {
+	buf[0] = linkAddr[0] ^ 2
+	buf[1] = linkAddr[1]
+	buf[2] = linkAddr[2]
+	buf[3] = 0xFE
+	buf[4] = 0xFE
+	buf[5] = linkAddr[3]
+	buf[6] = linkAddr[4]
+	buf[7] = linkAddr[5]
+}
+
+// EthernetAddressToEUI64 computes an EUI-64 from a 48-bit Ethernet/MAC address.
+func EthernetAddressToEUI64(linkAddr tcpip.LinkAddress) [IIDSize]byte {
+	var buf [IIDSize]byte
+	EthernetAdddressToEUI64IntoBuf(linkAddr, buf[:])
+	return buf
+}
+
 // LinkLocalAddr computes the default IPv6 link-local address from a link-layer
 // (MAC) address.
 func LinkLocalAddr(linkAddr tcpip.LinkAddress) tcpip.Address {
@@ -275,18 +309,11 @@ func LinkLocalAddr(linkAddr tcpip.LinkAddress) tcpip.Address {
 	// The conversion is very nearly:
 	//	aa:bb:cc:dd:ee:ff => FE80::Aabb:ccFF:FEdd:eeff
 	// Note the capital A. The conversion aa->Aa involves a bit flip.
-	lladdrb := [16]byte{
-		0:  0xFE,
-		1:  0x80,
-		8:  linkAddr[0] ^ 2,
-		9:  linkAddr[1],
-		10: linkAddr[2],
-		11: 0xFF,
-		12: 0xFE,
-		13: linkAddr[3],
-		14: linkAddr[4],
-		15: linkAddr[5],
+	lladdrb := [IPv6AddressSize]byte{
+		0: 0xFE,
+		1: 0x80,
 	}
+	EthernetAdddressToEUI64IntoBuf(linkAddr, lladdrb[IIDOffsetInIPv6Address:])
 	return tcpip.Address(lladdrb[:])
 }
 
diff --git a/pkg/tcpip/header/ndp_options.go b/pkg/tcpip/header/ndp_options.go
index 2652e7b67..06e0bace2 100644
--- a/pkg/tcpip/header/ndp_options.go
+++ b/pkg/tcpip/header/ndp_options.go
@@ -17,6 +17,7 @@ package header
 import (
 	"encoding/binary"
 	"errors"
+	"math"
 	"time"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -109,13 +110,13 @@ const (
 )
 
 var (
-	// NDPInfiniteLifetime is a value that represents
-	// infinity for the Valid and Preferred Lifetime fields in a NDP Prefix
-	// Information option. Its value is (2^32 - 1)s = 4294967295s
+	// NDPInfiniteLifetime is a value that represents infinity for the
+	// 4-byte lifetime fields found in various NDP options. Its value is
+	// (2^32 - 1)s = 4294967295s.
 	//
 	// This is a variable instead of a constant so that tests can change
 	// this value to a smaller value. It should only be modified by tests.
-	NDPInfiniteLifetime = time.Second * 4294967295
+	NDPInfiniteLifetime = time.Second * math.MaxUint32
 )
 
 // NDPOptionIterator is an iterator of NDPOption.