Validate router alert's data length

RFC 2711 specifies that the router alert's length field is always 2
so we should make sure only 2 bytes are read from a router alert
option's data field.

Test: header.TestIPv6OptionsExtHdrIterErr
PiperOrigin-RevId: 347727876

pkg/tcpip/header/ipv6_extension_headers.go

@@ -18,6 +18,7 @@ import (
 	"bufio"
 	"bytes"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"io"
 	"math"
@@ -274,6 +275,10 @@ func ipv6UnknownActionFromIdentifier(id IPv6ExtHdrOptionIdentifier) IPv6OptionUn
 	return IPv6OptionUnknownAction((id & ipv6UnknownExtHdrOptionActionMask) >> ipv6UnknownExtHdrOptionActionShift)
 }
 
+// ErrMalformedIPv6ExtHdrOption indicates that an IPv6 extension header option
+// is malformed.
+var ErrMalformedIPv6ExtHdrOption = errors.New("malformed IPv6 extension header option")
+
 // IPv6UnknownExtHdrOption holds the identifier and data for an IPv6 extension
 // header option that is unknown by the parsing utilities.
 type IPv6UnknownExtHdrOption struct {
@@ -351,10 +356,15 @@ func (i *IPv6OptionsExtHdrOptionsIterator) Next() (IPv6ExtHdrOption, bool, error
 			continue
 		case ipv6RouterAlertHopByHopOptionIdentifier:
 			var routerAlertValue [ipv6RouterAlertPayloadLength]byte
-			if n, err := i.reader.Read(routerAlertValue[:]); err != nil {
-				panic(fmt.Sprintf("error when reading RouterAlert option's data bytes: %s", err))
-			} else if n != ipv6RouterAlertPayloadLength {
-				return nil, true, fmt.Errorf("read %d bytes for RouterAlert option, expected %d", n, ipv6RouterAlertPayloadLength)
+			if n, err := io.ReadFull(&i.reader, routerAlertValue[:]); err != nil {
+				switch err {
+				case io.EOF, io.ErrUnexpectedEOF:
+					return nil, true, fmt.Errorf("got invalid length (%d) for router alert option (want = %d): %w", length, ipv6RouterAlertPayloadLength, ErrMalformedIPv6ExtHdrOption)
+				default:
+					return nil, true, fmt.Errorf("read %d out of %d option data bytes for router alert option: %w", n, ipv6RouterAlertPayloadLength, err)
+				}
+			} else if n != int(length) {
+				return nil, true, fmt.Errorf("got invalid length (%d) for router alert option (want = %d): %w", length, ipv6RouterAlertPayloadLength, ErrMalformedIPv6ExtHdrOption)
 			}
 			return &IPv6RouterAlertOption{Value: IPv6RouterAlertValue(binary.BigEndian.Uint16(routerAlertValue[:]))}, false, nil
 		default:

pkg/tcpip/header/ipv6_extension_headers_test.go

@@ -212,6 +212,31 @@ func TestIPv6OptionsExtHdrIterErr(t *testing.T) {
 			bytes: []byte{1, 3},
 			err:   io.ErrUnexpectedEOF,
 		},
+		{
+			name:  "Router alert without data",
+			bytes: []byte{byte(ipv6RouterAlertHopByHopOptionIdentifier), 0},
+			err:   ErrMalformedIPv6ExtHdrOption,
+		},
+		{
+			name:  "Router alert with partial data",
+			bytes: []byte{byte(ipv6RouterAlertHopByHopOptionIdentifier), 1, 1},
+			err:   ErrMalformedIPv6ExtHdrOption,
+		},
+		{
+			name:  "Router alert with partial data and Pad1",
+			bytes: []byte{byte(ipv6RouterAlertHopByHopOptionIdentifier), 1, 1, 0},
+			err:   ErrMalformedIPv6ExtHdrOption,
+		},
+		{
+			name:  "Router alert with extra data",
+			bytes: []byte{byte(ipv6RouterAlertHopByHopOptionIdentifier), 3, 1, 2, 3},
+			err:   ErrMalformedIPv6ExtHdrOption,
+		},
+		{
+			name:  "Router alert with missing data",
+			bytes: []byte{byte(ipv6RouterAlertHopByHopOptionIdentifier), 1},
+			err:   io.ErrUnexpectedEOF,
+		},
 	}
 
 	check := func(t *testing.T, it IPv6OptionsExtHdrOptionsIterator, expectedErr error) {