Support Hop By Hop and Destination Options ext hdr

Enables handling the Hop by Hop and Destination Options extension
headers, but options are not yet supported. All options will be
treated as unknown and their respective action will be followed.

Note, the stack does not yet support sending ICMPv6 error messages in
response to options that cannot be handled/parsed. That will come
in a later change (Issue #2211).

Tests:
- header_test.TestIPv6UnknownExtHdrOption
- header_test.TestIPv6OptionsExtHdrIterErr
- header_test.TestIPv6OptionsExtHdrIter
- ipv6_test.TestReceiveIPv6ExtHdrs
PiperOrigin-RevId: 303433085

2 files changed, 291 insertions, 14 deletions

diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index a703a768c..685239017 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -184,24 +184,61 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt stack.PacketBuffer) {
 	pkt.Data.TrimFront(header.IPv6MinimumSize)
 	pkt.Data.CapLength(int(h.PayloadLength()))
 
-	it, err := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(h.NextHeader()), pkt.Data, true)
-	if err != nil {
-		r.Stats().IP.MalformedPacketsReceived.Increment()
-		return
-	}
+	it := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(h.NextHeader()), pkt.Data)
 
-	for {
+	for firstHeader := true; ; firstHeader = false {
 		extHdr, done, err := it.Next()
 		if err != nil {
-			// This should never happen as MakeIPv6PayloadIterator above did not
-			// return an error.
-			panic(fmt.Sprintf("unexpected error when iterating over IPv6 payload: %s", err))
+			r.Stats().IP.MalformedPacketsReceived.Increment()
+			return
 		}
 		if done {
 			break
 		}
 
 		switch extHdr := extHdr.(type) {
+		case header.IPv6HopByHopOptionsExtHdr:
+			// As per RFC 8200 section 4.1, the Hop By Hop extension header is
+			// restricted to appear immediately after an IPv6 fixed header.
+			//
+			// TODO(b/152019344): Send an ICMPv6 Parameter Problem, Code 1
+			// (unrecognized next header) error in response to an extension header's
+			// Next Header field with the Hop By Hop extension header identifier.
+			if !firstHeader {
+				return
+			}
+
+			optsIt := extHdr.Iter()
+
+			for {
+				opt, done, err := optsIt.Next()
+				if err != nil {
+					r.Stats().IP.MalformedPacketsReceived.Increment()
+					return
+				}
+				if done {
+					break
+				}
+
+				// We currently do not support any IPv6 Hop By Hop extension header
+				// options.
+				switch opt.UnknownAction() {
+				case header.IPv6OptionUnknownActionSkip:
+				case header.IPv6OptionUnknownActionDiscard:
+					return
+				case header.IPv6OptionUnknownActionDiscardSendICMP:
+					// TODO(b/152019344): Send an ICMPv6 Parameter Problem Code 2 for
+					// unrecognized IPv6 extension header options.
+					return
+				case header.IPv6OptionUnknownActionDiscardSendICMPNoMulticastDest:
+					// TODO(b/152019344): Send an ICMPv6 Parameter Problem Code 2 for
+					// unrecognized IPv6 extension header options.
+					return
+				default:
+					panic(fmt.Sprintf("unrecognized action for an unrecognized Hop By Hop extension header option = %d", opt))
+				}
+			}
+
 		case header.IPv6RoutingExtHdr:
 			// As per RFC 8200 section 4.4, if a node encounters a routing header with
 			// an unrecognized routing type value, with a non-zero Segments Left
@@ -266,12 +303,39 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt stack.PacketBuffer) {
 				// We create a new iterator with the reassembled packet because we could
 				// have more extension headers in the reassembled payload, as per RFC
 				// 8200 section 4.5.
-				it, err = header.MakeIPv6PayloadIterator(rawPayload.Identifier, pkt.Data, true)
+				it = header.MakeIPv6PayloadIterator(rawPayload.Identifier, pkt.Data)
+			}
+
+		case header.IPv6DestinationOptionsExtHdr:
+			optsIt := extHdr.Iter()
+
+			for {
+				opt, done, err := optsIt.Next()
 				if err != nil {
 					r.Stats().IP.MalformedPacketsReceived.Increment()
-					r.Stats().IP.MalformedFragmentsReceived.Increment()
 					return
 				}
+				if done {
+					break
+				}
+
+				// We currently do not support any IPv6 Destination extension header
+				// options.
+				switch opt.UnknownAction() {
+				case header.IPv6OptionUnknownActionSkip:
+				case header.IPv6OptionUnknownActionDiscard:
+					return
+				case header.IPv6OptionUnknownActionDiscardSendICMP:
+					// TODO(b/152019344): Send an ICMPv6 Parameter Problem Code 2 for
+					// unrecognized IPv6 extension header options.
+					return
+				case header.IPv6OptionUnknownActionDiscardSendICMPNoMulticastDest:
+					// TODO(b/152019344): Send an ICMPv6 Parameter Problem Code 2 for
+					// unrecognized IPv6 extension header options.
+					return
+				default:
+					panic(fmt.Sprintf("unrecognized action for an unrecognized Destination extension header option = %d", opt))
+				}
 			}
 
 		case header.IPv6RawPayloadHeader:
diff --git a/pkg/tcpip/network/ipv6/ipv6_test.go b/pkg/tcpip/network/ipv6/ipv6_test.go
index 86bfda85e..37f7e53ce 100644
--- a/pkg/tcpip/network/ipv6/ipv6_test.go
+++ b/pkg/tcpip/network/ipv6/ipv6_test.go
@@ -37,9 +37,11 @@ const (
 
 	// Tests use the extension header identifier values as uint8 instead of
 	// header.IPv6ExtensionHeaderIdentifier.
-	routingExtHdrID  = uint8(header.IPv6RoutingExtHdrIdentifier)
-	fragmentExtHdrID = uint8(header.IPv6FragmentExtHdrIdentifier)
-	noNextHdrID      = uint8(header.IPv6NoNextHeaderIdentifier)
+	hopByHopExtHdrID    = uint8(header.IPv6HopByHopOptionsExtHdrIdentifier)
+	routingExtHdrID     = uint8(header.IPv6RoutingExtHdrIdentifier)
+	fragmentExtHdrID    = uint8(header.IPv6FragmentExtHdrIdentifier)
+	destinationExtHdrID = uint8(header.IPv6DestinationOptionsExtHdrIdentifier)
+	noNextHdrID         = uint8(header.IPv6NoNextHeaderIdentifier)
 )
 
 // testReceiveICMP tests receiving an ICMP packet from src to dst. want is the
@@ -290,6 +292,67 @@ func TestReceiveIPv6ExtHdrs(t *testing.T) {
 			shouldAccept: true,
 		},
 		{
+			name: "hopbyhop with unknown option skippable action",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					nextHdr, 1,
+
+					// Skippable unknown.
+					63, 4, 1, 2, 3, 4,
+
+					// Skippable unknown.
+					62, 6, 1, 2, 3, 4, 5, 6,
+				}, hopByHopExtHdrID
+			},
+			shouldAccept: true,
+		},
+		{
+			name: "hopbyhop with unknown option discard action",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					nextHdr, 1,
+
+					// Skippable unknown.
+					63, 4, 1, 2, 3, 4,
+
+					// Discard unknown.
+					127, 6, 1, 2, 3, 4, 5, 6,
+				}, hopByHopExtHdrID
+			},
+			shouldAccept: false,
+		},
+		{
+			name: "hopbyhop with unknown option discard and send icmp action",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					nextHdr, 1,
+
+					// Skippable unknown.
+					63, 4, 1, 2, 3, 4,
+
+					// Discard & send ICMP if option is unknown.
+					191, 6, 1, 2, 3, 4, 5, 6,
+				}, hopByHopExtHdrID
+			},
+			shouldAccept: false,
+		},
+		{
+			name: "hopbyhop with unknown option discard and send icmp action unless multicast dest",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					nextHdr, 1,
+
+					// Skippable unknown.
+					63, 4, 1, 2, 3, 4,
+
+					// Discard & send ICMP unless packet is for multicast destination if
+					// option is unknown.
+					255, 6, 1, 2, 3, 4, 5, 6,
+				}, hopByHopExtHdrID
+			},
+			shouldAccept: false,
+		},
+		{
 			name:         "routing with zero segments left",
 			extHdr:       func(nextHdr uint8) ([]byte, uint8) { return []byte{nextHdr, 0, 1, 0, 2, 3, 4, 5}, routingExtHdrID },
 			shouldAccept: true,
@@ -315,6 +378,72 @@ func TestReceiveIPv6ExtHdrs(t *testing.T) {
 			shouldAccept: false,
 		},
 		{
+			name:         "No next header",
+			extHdr:       func(nextHdr uint8) ([]byte, uint8) { return []byte{}, noNextHdrID },
+			shouldAccept: false,
+		},
+		{
+			name: "destination with unknown option skippable action",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					nextHdr, 1,
+
+					// Skippable unknown.
+					63, 4, 1, 2, 3, 4,
+
+					// Skippable unknown.
+					62, 6, 1, 2, 3, 4, 5, 6,
+				}, destinationExtHdrID
+			},
+			shouldAccept: true,
+		},
+		{
+			name: "destination with unknown option discard action",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					nextHdr, 1,
+
+					// Skippable unknown.
+					63, 4, 1, 2, 3, 4,
+
+					// Discard unknown.
+					127, 6, 1, 2, 3, 4, 5, 6,
+				}, destinationExtHdrID
+			},
+			shouldAccept: false,
+		},
+		{
+			name: "destination with unknown option discard and send icmp action",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					nextHdr, 1,
+
+					// Skippable unknown.
+					63, 4, 1, 2, 3, 4,
+
+					// Discard & send ICMP if option is unknown.
+					191, 6, 1, 2, 3, 4, 5, 6,
+				}, destinationExtHdrID
+			},
+			shouldAccept: false,
+		},
+		{
+			name: "destination with unknown option discard and send icmp action unless multicast dest",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					nextHdr, 1,
+
+					// Skippable unknown.
+					63, 4, 1, 2, 3, 4,
+
+					// Discard & send ICMP unless packet is for multicast destination if
+					// option is unknown.
+					255, 6, 1, 2, 3, 4, 5, 6,
+				}, destinationExtHdrID
+			},
+			shouldAccept: false,
+		},
+		{
 			name: "routing - atomic fragment",
 			extHdr: func(nextHdr uint8) ([]byte, uint8) {
 				return []byte{
@@ -341,10 +470,94 @@ func TestReceiveIPv6ExtHdrs(t *testing.T) {
 			shouldAccept: true,
 		},
 		{
+			name: "hop by hop (with skippable unknown) - routing",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					// Hop By Hop extension header with skippable unknown option.
+					routingExtHdrID, 0, 62, 4, 1, 2, 3, 4,
+
+					// Routing extension header.
+					nextHdr, 0, 1, 0, 2, 3, 4, 5,
+				}, hopByHopExtHdrID
+			},
+			shouldAccept: true,
+		},
+		{
+			name: "routing - hop by hop (with skippable unknown)",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					// Routing extension header.
+					hopByHopExtHdrID, 0, 1, 0, 2, 3, 4, 5,
+
+					// Hop By Hop extension header with skippable unknown option.
+					nextHdr, 0, 62, 4, 1, 2, 3, 4,
+				}, routingExtHdrID
+			},
+			shouldAccept: false,
+		},
+		{
 			name:         "No next header",
 			extHdr:       func(nextHdr uint8) ([]byte, uint8) { return []byte{}, noNextHdrID },
 			shouldAccept: false,
 		},
+		{
+			name: "hopbyhop (with skippable unknown) - routing - atomic fragment - destination (with skippable unknown)",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					// Hop By Hop extension header with skippable unknown option.
+					routingExtHdrID, 0, 62, 4, 1, 2, 3, 4,
+
+					// Routing extension header.
+					fragmentExtHdrID, 0, 1, 0, 2, 3, 4, 5,
+
+					// Fragment extension header.
+					destinationExtHdrID, 0, 0, 0, 1, 2, 3, 4,
+
+					// Destination extension header with skippable unknown option.
+					nextHdr, 0, 63, 4, 1, 2, 3, 4,
+				}, hopByHopExtHdrID
+			},
+			shouldAccept: true,
+		},
+		{
+			name: "hopbyhop (with discard unknown) - routing - atomic fragment - destination (with skippable unknown)",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					// Hop By Hop extension header with discard action for unknown option.
+					routingExtHdrID, 0, 65, 4, 1, 2, 3, 4,
+
+					// Routing extension header.
+					fragmentExtHdrID, 0, 1, 0, 2, 3, 4, 5,
+
+					// Fragment extension header.
+					destinationExtHdrID, 0, 0, 0, 1, 2, 3, 4,
+
+					// Destination extension header with skippable unknown option.
+					nextHdr, 0, 63, 4, 1, 2, 3, 4,
+				}, hopByHopExtHdrID
+			},
+			shouldAccept: false,
+		},
+		{
+			name: "hopbyhop (with skippable unknown) - routing - atomic fragment - destination (with discard unknown)",
+			extHdr: func(nextHdr uint8) ([]byte, uint8) {
+				return []byte{
+					// Hop By Hop extension header with skippable unknown option.
+					routingExtHdrID, 0, 62, 4, 1, 2, 3, 4,
+
+					// Routing extension header.
+					fragmentExtHdrID, 0, 1, 0, 2, 3, 4, 5,
+
+					// Fragment extension header.
+					destinationExtHdrID, 0, 0, 0, 1, 2, 3, 4,
+
+					// Destination extension header with discard action for unknown
+					// option.
+					nextHdr, 0, 65, 4, 1, 2, 3, 4,
+				}, hopByHopExtHdrID
+			},
+			shouldAccept: false,
+		},
 	}
 
 	for _, test := range tests {