Change the way the IP options report problems

The error messages are not needed or used as these are not processing errors
so much as errors to be reported back to the packet sender. Implicitly
describe whether each error should generate ICMP packets or not. Most do
but there are a couple that do not.

Slightly alter some test expectations for Linux compatibility and add a
couple more. Improve Linux compatibility on error packet returns. Some
cosmetic changes to tests to match the upcoming packet impact version
of the same tests.

PiperOrigin-RevId: 352889785

1 files changed, 30 insertions, 28 deletions

diff --git a/pkg/tcpip/header/ipv4.go b/pkg/tcpip/header/ipv4.go
index e6103f4bc..48ca60319 100644
--- a/pkg/tcpip/header/ipv4.go
+++ b/pkg/tcpip/header/ipv4.go
@@ -1,4 +1,4 @@
-// Copyright 2018 The gVisor Authors.
+// Copyright 2021 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.
@@ -16,7 +16,6 @@ package header
 
 import (
 	"encoding/binary"
-	"errors"
 	"fmt"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -481,15 +480,13 @@ const (
 	IPv4OptionLengthOffset = 1
 )
 
-// Potential errors when parsing generic IP options.
-var (
-	ErrIPv4OptZeroLength   = errors.New("zero length IP option")
-	ErrIPv4OptDuplicate    = errors.New("duplicate IP option")
-	ErrIPv4OptInvalid      = errors.New("invalid IP option")
-	ErrIPv4OptMalformed    = errors.New("malformed IP option")
-	ErrIPv4OptionTruncated = errors.New("truncated IP option")
-	ErrIPv4OptionAddress   = errors.New("bad IP option address")
-)
+// IPv4OptParameterProblem indicates that a Parameter Problem message
+// should be generated, and gives the offset in the current entity
+// that should be used in that packet.
+type IPv4OptParameterProblem struct {
+	Pointer  uint8
+	NeedICMP bool
+}
 
 // IPv4Option is an interface representing various option types.
 type IPv4Option interface {
@@ -583,8 +580,9 @@ func (i *IPv4OptionIterator) Finalize() IPv4Options {
 // It returns
 // - A slice of bytes holding the next option or nil if there is error.
 // - A boolean which is true if parsing of all the options is complete.
-// - An error which is non-nil if an error condition was encountered.
-func (i *IPv4OptionIterator) Next() (IPv4Option, bool, error) {
+//   Undefined in the case of error.
+// - An error indication which is non-nil if an error condition was found.
+func (i *IPv4OptionIterator) Next() (IPv4Option, bool, *IPv4OptParameterProblem) {
 	// The opts slice gets shorter as we process the options. When we have no
 	// bytes left we are done.
 	if len(i.options) == 0 {
@@ -606,24 +604,22 @@ func (i *IPv4OptionIterator) Next() (IPv4Option, bool, error) {
 	// There are no more single byte options defined.  All the rest have a length
 	// field so we need to sanity check it.
 	if len(i.options) == 1 {
-		return nil, true, ErrIPv4OptMalformed
+		return nil, false, &IPv4OptParameterProblem{
+			Pointer:  i.ErrCursor,
+			NeedICMP: true,
+		}
 	}
 
 	optLen := i.options[IPv4OptionLengthOffset]
 
-	if optLen == 0 {
-		i.ErrCursor++
-		return nil, true, ErrIPv4OptZeroLength
-	}
+	if optLen <= IPv4OptionLengthOffset || optLen > uint8(len(i.options)) {
+		// The actual error is in the length (2nd byte of the option) but we
+		// return the start of the option for compatibility with Linux.
 
-	if optLen == 1 {
-		i.ErrCursor++
-		return nil, true, ErrIPv4OptMalformed
-	}
-
-	if optLen > uint8(len(i.options)) {
-		i.ErrCursor++
-		return nil, true, ErrIPv4OptionTruncated
+		return nil, false, &IPv4OptParameterProblem{
+			Pointer:  i.ErrCursor,
+			NeedICMP: true,
+		}
 	}
 
 	optionBody := i.options[:optLen]
@@ -635,7 +631,10 @@ func (i *IPv4OptionIterator) Next() (IPv4Option, bool, error) {
 	case IPv4OptionTimestampType:
 		if optLen < IPv4OptionTimestampHdrLength {
 			i.ErrCursor++
-			return nil, true, ErrIPv4OptMalformed
+			return nil, false, &IPv4OptParameterProblem{
+				Pointer:  i.ErrCursor,
+				NeedICMP: true,
+			}
 		}
 		retval := IPv4OptionTimestamp(optionBody)
 		return &retval, false, nil
@@ -643,7 +642,10 @@ func (i *IPv4OptionIterator) Next() (IPv4Option, bool, error) {
 	case IPv4OptionRecordRouteType:
 		if optLen < IPv4OptionRecordRouteHdrLength {
 			i.ErrCursor++
-			return nil, true, ErrIPv4OptMalformed
+			return nil, false, &IPv4OptParameterProblem{
+				Pointer:  i.ErrCursor,
+				NeedICMP: true,
+			}
 		}
 		retval := IPv4OptionRecordRoute(optionBody)
 		return &retval, false, nil