Add a type to represent the NDP Recursive DNS Server option

This change adds a type to represent the NDP Recursive DNS Server option, as
defined by RFC 8106 section 5.1.

PiperOrigin-RevId: 284005493

5 files changed, 339 insertions, 11 deletions

diff --git a/pkg/tcpip/header/BUILD b/pkg/tcpip/header/BUILD
index a3485b35c..8392cb9e5 100644
--- a/pkg/tcpip/header/BUILD
+++ b/pkg/tcpip/header/BUILD
@@ -55,5 +55,8 @@ go_test(
         "ndp_test.go",
     ],
     embed = [":header"],
-    deps = ["//pkg/tcpip"],
+    deps = [
+        "//pkg/tcpip",
+        "@com_github_google_go-cmp//cmp:go_default_library",
+    ],
 )
diff --git a/pkg/tcpip/header/ndp_options.go b/pkg/tcpip/header/ndp_options.go
index 1ca6199ef..2652e7b67 100644
--- a/pkg/tcpip/header/ndp_options.go
+++ b/pkg/tcpip/header/ndp_options.go
@@ -85,6 +85,23 @@ const (
 	// within an NDPPrefixInformation.
 	ndpPrefixInformationPrefixOffset = 14
 
+	// NDPRecursiveDNSServerOptionType is the type of the Recursive DNS
+	// Server option, as per RFC 8106 section 5.1.
+	NDPRecursiveDNSServerOptionType = 25
+
+	// ndpRecursiveDNSServerLifetimeOffset is the start of the 4-byte
+	// Lifetime field within an NDPRecursiveDNSServer.
+	ndpRecursiveDNSServerLifetimeOffset = 2
+
+	// ndpRecursiveDNSServerAddressesOffset is the start of the addresses
+	// for IPv6 Recursive DNS Servers within an NDPRecursiveDNSServer.
+	ndpRecursiveDNSServerAddressesOffset = 6
+
+	// minNDPRecursiveDNSServerLength is the minimum NDP Recursive DNS
+	// Server option's length field value when it contains at least one
+	// IPv6 address.
+	minNDPRecursiveDNSServerLength = 3
+
 	// 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.
@@ -92,13 +109,13 @@ const (
 )
 
 var (
-	// NDPPrefixInformationInfiniteLifetime is a value that represents
+	// 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
 	//
 	// 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.
-	NDPPrefixInformationInfiniteLifetime = time.Second * 4294967295
+	NDPInfiniteLifetime = time.Second * 4294967295
 )
 
 // NDPOptionIterator is an iterator of NDPOption.
@@ -118,6 +135,7 @@ var (
 	ErrNDPOptBufExhausted  = errors.New("Buffer unexpectedly exhausted")
 	ErrNDPOptZeroLength    = errors.New("NDP option has zero-valued Length field")
 	ErrNDPOptMalformedBody = errors.New("NDP option has a malformed body")
+	ErrNDPInvalidLength    = errors.New("NDP option's Length value is invalid as per relevant RFC")
 )
 
 // Next returns the next element in the backing NDPOptions, or true if we are
@@ -182,6 +200,22 @@ func (i *NDPOptionIterator) Next() (NDPOption, bool, error) {
 			}
 
 			return NDPPrefixInformation(body), false, nil
+
+		case NDPRecursiveDNSServerOptionType:
+			// RFC 8106 section 5.3.1 outlines that the RDNSS option
+			// must have a minimum length of 3 so it contains at
+			// least one IPv6 address.
+			if l < minNDPRecursiveDNSServerLength {
+				return nil, true, ErrNDPInvalidLength
+			}
+
+			opt := NDPRecursiveDNSServer(body)
+			if len(opt.Addresses()) == 0 {
+				return nil, true, ErrNDPOptMalformedBody
+			}
+
+			return opt, false, nil
+
 		default:
 			// We do not yet recognize the option, just skip for
 			// now. This is okay because RFC 4861 allows us to
@@ -434,7 +468,7 @@ func (o NDPPrefixInformation) AutonomousAddressConfigurationFlag() bool {
 //
 // Note, a value of 0 implies the prefix should not be considered as on-link,
 // and a value of infinity/forever is represented by
-// NDPPrefixInformationInfiniteLifetime.
+// NDPInfiniteLifetime.
 func (o NDPPrefixInformation) ValidLifetime() time.Duration {
 	// The field is the time in seconds, as per RFC 4861 section 4.6.2.
 	return time.Second * time.Duration(binary.BigEndian.Uint32(o[ndpPrefixInformationValidLifetimeOffset:]))
@@ -447,7 +481,7 @@ func (o NDPPrefixInformation) ValidLifetime() time.Duration {
 //
 // Note, a value of 0 implies that addresses generated from the prefix should
 // no longer remain preferred, and a value of infinity is represented by
-// NDPPrefixInformationInfiniteLifetime.
+// NDPInfiniteLifetime.
 //
 // Also note that the value of this field MUST NOT exceed the Valid Lifetime
 // field to avoid preferring addresses that are no longer valid, for the
@@ -476,3 +510,79 @@ func (o NDPPrefixInformation) Subnet() tcpip.Subnet {
 	}
 	return addrWithPrefix.Subnet()
 }
+
+// NDPRecursiveDNSServer is the NDP Recursive DNS Server option, as defined by
+// RFC 8106 section 5.1.
+//
+// To make sure that the option meets its minimum length and does not end in the
+// middle of a DNS server's IPv6 address, the length of a valid
+// NDPRecursiveDNSServer must meet the following constraint:
+//   (Length - ndpRecursiveDNSServerAddressesOffset) % IPv6AddressSize == 0
+type NDPRecursiveDNSServer []byte
+
+// Type returns the type of an NDP Recursive DNS Server option.
+//
+// Type implements NDPOption.Type.
+func (NDPRecursiveDNSServer) Type() uint8 {
+	return NDPRecursiveDNSServerOptionType
+}
+
+// Length implements NDPOption.Length.
+func (o NDPRecursiveDNSServer) Length() int {
+	return len(o)
+}
+
+// serializeInto implements NDPOption.serializeInto.
+func (o NDPRecursiveDNSServer) serializeInto(b []byte) int {
+	used := copy(b, o)
+
+	// Zero out the reserved bytes that are before the Lifetime field.
+	for i := 0; i < ndpRecursiveDNSServerLifetimeOffset; i++ {
+		b[i] = 0
+	}
+
+	return used
+}
+
+// Lifetime returns the length of time that the DNS server addresses
+// in this option may be used for name resolution.
+//
+// Note, a value of 0 implies the addresses should no longer be used,
+// and a value of infinity/forever is represented by NDPInfiniteLifetime.
+//
+// Lifetime may panic if o does not have enough bytes to hold the Lifetime
+// field.
+func (o NDPRecursiveDNSServer) Lifetime() time.Duration {
+	// The field is the time in seconds, as per RFC 8106 section 5.1.
+	return time.Second * time.Duration(binary.BigEndian.Uint32(o[ndpRecursiveDNSServerLifetimeOffset:]))
+}
+
+// Addresses returns the recursive DNS server IPv6 addresses that may be
+// used for name resolution.
+//
+// Note, some of the addresses returned MAY be link-local addresses.
+//
+// Addresses may panic if o does not hold valid IPv6 addresses.
+func (o NDPRecursiveDNSServer) Addresses() []tcpip.Address {
+	l := len(o)
+	if l < ndpRecursiveDNSServerAddressesOffset {
+		return nil
+	}
+
+	l -= ndpRecursiveDNSServerAddressesOffset
+	if l%IPv6AddressSize != 0 {
+		return nil
+	}
+
+	buf := o[ndpRecursiveDNSServerAddressesOffset:]
+	var addrs []tcpip.Address
+	for len(buf) > 0 {
+		addr := tcpip.Address(buf[:IPv6AddressSize])
+		if !IsV6UnicastAddress(addr) {
+			return nil
+		}
+		addrs = append(addrs, addr)
+		buf = buf[IPv6AddressSize:]
+	}
+	return addrs
+}
diff --git a/pkg/tcpip/header/ndp_test.go b/pkg/tcpip/header/ndp_test.go
index ad6daafcd..2c439d70c 100644
--- a/pkg/tcpip/header/ndp_test.go
+++ b/pkg/tcpip/header/ndp_test.go
@@ -19,6 +19,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/google/go-cmp/cmp"
 	"gvisor.dev/gvisor/pkg/tcpip"
 )
 
@@ -369,6 +370,175 @@ func TestNDPPrefixInformationOption(t *testing.T) {
 	}
 }
 
+func TestNDPRecursiveDNSServerOptionSerialize(t *testing.T) {
+	b := []byte{
+		9, 8,
+		1, 2, 4, 8,
+		0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+	}
+	targetBuf := []byte{1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}
+	expected := []byte{
+		25, 3, 0, 0,
+		1, 2, 4, 8,
+		0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+	}
+	opts := NDPOptions(targetBuf)
+	serializer := NDPOptionsSerializer{
+		NDPRecursiveDNSServer(b),
+	}
+	if got, want := opts.Serialize(serializer), len(expected); got != want {
+		t.Errorf("got Serialize = %d, want = %d", got, want)
+	}
+	if !bytes.Equal(targetBuf, expected) {
+		t.Fatalf("got targetBuf = %x, want = %x", targetBuf, expected)
+	}
+
+	it, err := opts.Iter(true)
+	if err != nil {
+		t.Fatalf("got Iter = (_, %s), want = (_, nil)", err)
+	}
+
+	next, done, err := it.Next()
+	if err != nil {
+		t.Fatalf("got Next = (_, _, %s), want = (_, _, nil)", err)
+	}
+	if done {
+		t.Fatal("got Next = (_, true, _), want = (_, false, _)")
+	}
+	if got := next.Type(); got != NDPRecursiveDNSServerOptionType {
+		t.Errorf("got Type = %d, want = %d", got, NDPRecursiveDNSServerOptionType)
+	}
+
+	opt, ok := next.(NDPRecursiveDNSServer)
+	if !ok {
+		t.Fatalf("next (type = %T) cannot be casted to an NDPRecursiveDNSServer", next)
+	}
+	if got := opt.Type(); got != 25 {
+		t.Errorf("got Type = %d, want = 31", got)
+	}
+	if got := opt.Length(); got != 22 {
+		t.Errorf("got Length = %d, want = 22", got)
+	}
+	if got, want := opt.Lifetime(), 16909320*time.Second; got != want {
+		t.Errorf("got Lifetime = %s, want = %s", got, want)
+	}
+	want := []tcpip.Address{
+		"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
+	}
+	if got := opt.Addresses(); !cmp.Equal(got, want) {
+		t.Errorf("got Addresses = %v, want = %v", got, want)
+	}
+
+	// Iterator should not return anything else.
+	next, done, err = it.Next()
+	if err != nil {
+		t.Errorf("got Next = (_, _, %s), want = (_, _, nil)", err)
+	}
+	if !done {
+		t.Error("got Next = (_, false, _), want = (_, true, _)")
+	}
+	if next != nil {
+		t.Errorf("got Next = (%x, _, _), want = (nil, _, _)", next)
+	}
+}
+
+func TestNDPRecursiveDNSServerOption(t *testing.T) {
+	tests := []struct {
+		name     string
+		buf      []byte
+		lifetime time.Duration
+		addrs    []tcpip.Address
+	}{
+		{
+			"Valid1Addr",
+			[]byte{
+				25, 3, 0, 0,
+				0, 0, 0, 0,
+				0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+			},
+			0,
+			[]tcpip.Address{
+				"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
+			},
+		},
+		{
+			"Valid2Addr",
+			[]byte{
+				25, 5, 0, 0,
+				0, 0, 0, 0,
+				0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+				17, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16,
+			},
+			0,
+			[]tcpip.Address{
+				"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
+				"\x11\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x10",
+			},
+		},
+		{
+			"Valid3Addr",
+			[]byte{
+				25, 7, 0, 0,
+				0, 0, 0, 0,
+				0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+				17, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16,
+				17, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 17,
+			},
+			0,
+			[]tcpip.Address{
+				"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f",
+				"\x11\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x10",
+				"\x11\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x11",
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			opts := NDPOptions(test.buf)
+			it, err := opts.Iter(true)
+			if err != nil {
+				t.Fatalf("got Iter = (_, %s), want = (_, nil)", err)
+			}
+
+			// Iterator should get our option.
+			next, done, err := it.Next()
+			if err != nil {
+				t.Fatalf("got Next = (_, _, %s), want = (_, _, nil)", err)
+			}
+			if done {
+				t.Fatal("got Next = (_, true, _), want = (_, false, _)")
+			}
+			if got := next.Type(); got != NDPRecursiveDNSServerOptionType {
+				t.Fatalf("got Type %= %d, want = %d", got, NDPRecursiveDNSServerOptionType)
+			}
+
+			opt, ok := next.(NDPRecursiveDNSServer)
+			if !ok {
+				t.Fatalf("next (type = %T) cannot be casted to an NDPRecursiveDNSServer", next)
+			}
+			if got := opt.Lifetime(); got != test.lifetime {
+				t.Errorf("got Lifetime = %d, want = %d", got, test.lifetime)
+			}
+			if got := opt.Addresses(); !cmp.Equal(got, test.addrs) {
+				t.Errorf("got Addresses = %v, want = %v", got, test.addrs)
+			}
+
+			// Iterator should not return anything else.
+			next, done, err = it.Next()
+			if err != nil {
+				t.Errorf("got Next = (_, _, %s), want = (_, _, nil)", err)
+			}
+			if !done {
+				t.Error("got Next = (_, false, _), want = (_, true, _)")
+			}
+			if next != nil {
+				t.Errorf("got Next = (%x, _, _), want = (nil, _, _)", next)
+			}
+		})
+	}
+}
+
 // TestNDPOptionsIterCheck tests that Iter will return false if the NDPOptions
 // the iterator was returned for is malformed.
 func TestNDPOptionsIterCheck(t *testing.T) {
@@ -473,6 +643,51 @@ func TestNDPOptionsIterCheck(t *testing.T) {
 			},
 			nil,
 		},
+		{
+			"InvalidRecursiveDNSServerCutsOffAddress",
+			[]byte{
+				25, 4, 0, 0,
+				0, 0, 0, 0,
+				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
+				0, 1, 2, 3, 4, 5, 6, 7,
+			},
+			ErrNDPOptMalformedBody,
+		},
+		{
+			"InvalidRecursiveDNSServerInvalidLengthField",
+			[]byte{
+				25, 2, 0, 0,
+				0, 0, 0, 0,
+				0, 1, 2, 3, 4, 5, 6, 7, 8,
+			},
+			ErrNDPInvalidLength,
+		},
+		{
+			"RecursiveDNSServerTooSmall",
+			[]byte{
+				25, 1, 0, 0,
+				0, 0, 0,
+			},
+			ErrNDPOptBufExhausted,
+		},
+		{
+			"RecursiveDNSServerMulticast",
+			[]byte{
+				25, 3, 0, 0,
+				0, 0, 0, 0,
+				255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,
+			},
+			ErrNDPOptMalformedBody,
+		},
+		{
+			"RecursiveDNSServerUnspecified",
+			[]byte{
+				25, 3, 0, 0,
+				0, 0, 0, 0,
+				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+			},
+			ErrNDPOptMalformedBody,
+		},
 	}
 
 	for _, test := range tests {
diff --git a/pkg/tcpip/stack/ndp.go b/pkg/tcpip/stack/ndp.go
index cfdd0496e..1d202deb5 100644
--- a/pkg/tcpip/stack/ndp.go
+++ b/pkg/tcpip/stack/ndp.go
@@ -596,7 +596,7 @@ func (ndp *ndpState) handleRA(ip tcpip.Address, ra header.NDPRouterAdvert) {
 			// Update the invalidation timer.
 			timer := prefixState.invalidationTimer
 
-			if timer == nil && vl >= header.NDPPrefixInformationInfiniteLifetime {
+			if timer == nil && vl >= header.NDPInfiniteLifetime {
 				// Had infinite valid lifetime before and
 				// continues to have an invalid lifetime. Do
 				// nothing further.
@@ -615,7 +615,7 @@ func (ndp *ndpState) handleRA(ip tcpip.Address, ra header.NDPRouterAdvert) {
 				*prefixState.doNotInvalidate = true
 			}
 
-			if vl >= header.NDPPrefixInformationInfiniteLifetime {
+			if vl >= header.NDPInfiniteLifetime {
 				// Prefix is now valid forever so we don't need
 				// an invalidation timer.
 				prefixState.invalidationTimer = nil
@@ -734,7 +734,7 @@ func (ndp *ndpState) rememberOnLinkPrefix(prefix tcpip.Subnet, l time.Duration)
 	var timer *time.Timer
 
 	// Only create a timer if the lifetime is not infinite.
-	if l < header.NDPPrefixInformationInfiniteLifetime {
+	if l < header.NDPInfiniteLifetime {
 		timer = ndp.prefixInvalidationCallback(prefix, l, &doNotInvalidate)
 	}
 
diff --git a/pkg/tcpip/stack/ndp_test.go b/pkg/tcpip/stack/ndp_test.go
index 5b901f947..b2af78212 100644
--- a/pkg/tcpip/stack/ndp_test.go
+++ b/pkg/tcpip/stack/ndp_test.go
@@ -1364,10 +1364,10 @@ func TestPrefixDiscoveryWithInfiniteLifetime(t *testing.T) {
 	// invalidate the prefix.
 	const testInfiniteLifetimeSeconds = 2
 	const testInfiniteLifetime = testInfiniteLifetimeSeconds * time.Second
-	saved := header.NDPPrefixInformationInfiniteLifetime
-	header.NDPPrefixInformationInfiniteLifetime = testInfiniteLifetime
+	saved := header.NDPInfiniteLifetime
+	header.NDPInfiniteLifetime = testInfiniteLifetime
 	defer func() {
-		header.NDPPrefixInformationInfiniteLifetime = saved
+		header.NDPInfiniteLifetime = saved
 	}()
 
 	prefix := tcpip.AddressWithPrefix{