netlink: add argument length checks to AttributeEncoder calls

Updates #191

Signed-off-by: Matt Layher <[email protected]>

attribute.go

@@ -4,6 +4,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"math"
 
 	"github.com/josharian/native"
 	"github.com/mdlayher/netlink/nlenc"
@@ -619,6 +620,12 @@ func (ae *AttributeEncoder) String(typ uint16, s string) {
 		return
 	}
 
+	// Length checking, thanks ubiquitousbyte on GitHub.
+	if len(s) > math.MaxUint16-nlaHeaderLen {
+		ae.err = errors.New("string is too large to fit in a netlink attribute")
+		return
+	}
+
 	ae.attrs = append(ae.attrs, Attribute{
 		Type: typ,
 		Data: nlenc.Bytes(s),
@@ -631,6 +638,11 @@ func (ae *AttributeEncoder) Bytes(typ uint16, b []byte) {
 		return
 	}
 
+	if len(b) > math.MaxUint16-nlaHeaderLen {
+		ae.err = errors.New("byte slice is too large to fit in a netlink attribute")
+		return
+	}
+
 	ae.attrs = append(ae.attrs, Attribute{
 		Type: typ,
 		Data: b,
@@ -654,6 +666,11 @@ func (ae *AttributeEncoder) Do(typ uint16, fn func() ([]byte, error)) {
 		return
 	}
 
+	if len(b) > math.MaxUint16-nlaHeaderLen {
+		ae.err = errors.New("byte slice produced by Do is too large to fit in a netlink attribute")
+		return
+	}
+
 	ae.attrs = append(ae.attrs, Attribute{
 		Type: typ,
 		Data: b,

attribute_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"errors"
+	"math"
 	"reflect"
 	"testing"
 	"unsafe"
@@ -957,7 +958,27 @@ func TestAttributeEncoderError(t *testing.T) {
 		fn   func(ae *AttributeEncoder)
 	}{
 		{
-			name: "do",
+			name: "bytes length",
+			fn: func(ae *AttributeEncoder) {
+				ae.Bytes(1, make([]byte, math.MaxUint16))
+			},
+		},
+		{
+			name: "string length",
+			fn: func(ae *AttributeEncoder) {
+				ae.String(1, string(make([]byte, math.MaxUint16)))
+			},
+		},
+		{
+			name: "do length",
+			fn: func(ae *AttributeEncoder) {
+				ae.Do(1, func() ([]byte, error) {
+					return make([]byte, math.MaxUint16), nil
+				})
+			},
+		},
+		{
+			name: "do function",
 			fn: func(ae *AttributeEncoder) {
 				ae.Do(1, func() ([]byte, error) {
 					return nil, errors.New("testing error")