encoding/gob: more checks for corrupted data

Also unify the tests where possible to make it easy to add more.

Fixes #10273.

Change-Id: Idfa4f4a5dcaa05974066bafe17bed6cdd2ebedb7
Reviewed-on: https://go-review.googlesource.com/8662Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/encoding/gob/decode.go

@@ -682,7 +682,11 @@ func (dec *Decoder) decodeInterface(ityp reflect.Type, state *decoderState, valu
 // ignoreInterface discards the data for an interface value with no destination.
 func (dec *Decoder) ignoreInterface(state *decoderState) {
 	// Read the name of the concrete type.
-	b := make([]byte, state.decodeUint())
+	n, ok := state.getLength()
+	if !ok {
+		errorf("bad interface encoding: name too large for buffer")
+	}
+	b := make([]byte, n)
 	_, err := state.b.Read(b)
 	if err != nil {
 		error_(err)
@@ -692,9 +696,9 @@ func (dec *Decoder) ignoreInterface(state *decoderState) {
 		error_(dec.err)
 	}
 	// At this point, the decoder buffer contains a delimited value. Just toss it.
-	n, ok := state.getLength()
+	n, ok = state.getLength()
 	if !ok {
-		errorf("bad interface encoding: length too large for buffer")
+		errorf("bad interface encoding: data length too large for buffer")
 	}
 	state.b.Drop(n)
 }
@@ -703,7 +707,11 @@ func (dec *Decoder) ignoreInterface(state *decoderState) {
 // The data is encoded as a byte slice.
 func (dec *Decoder) decodeGobDecoder(ut *userTypeInfo, state *decoderState, value reflect.Value) {
 	// Read the bytes for the value.
-	b := make([]byte, state.decodeUint())
+	n, ok := state.getLength()
+	if !ok {
+		errorf("GobDecoder: length too large for buffer")
+	}
+	b := make([]byte, n)
 	_, err := state.b.Read(b)
 	if err != nil {
 		error_(err)
@@ -725,7 +733,11 @@ func (dec *Decoder) decodeGobDecoder(ut *userTypeInfo, state *decoderState, valu
 // ignoreGobDecoder discards the data for a GobDecoder value with no destination.
 func (dec *Decoder) ignoreGobDecoder(state *decoderState) {
 	// Read the bytes for the value.
-	b := make([]byte, state.decodeUint())
+	n, ok := state.getLength()
+	if !ok {
+		errorf("GobDecoder: length too large for buffer")
+	}
+	b := make([]byte, n)
 	_, err := state.b.Read(b)
 	if err != nil {
 		error_(err)

src/encoding/gob/encoder_test.go

@@ -6,8 +6,8 @@ package gob
 
 import (
 	"bytes"
+	"encoding/hex"
 	"fmt"
-	"io"
 	"reflect"
 	"strings"
 	"testing"
@@ -187,24 +187,6 @@ func TestWrongTypeDecoder(t *testing.T) {
 	badTypeCheck(new(ET4), true, "different type of field", t)
 }
 
-func corruptDataCheck(s string, err error, t *testing.T) {
-	b := bytes.NewBufferString(s)
-	dec := NewDecoder(b)
-	err1 := dec.Decode(new(ET2))
-	if err1 != err {
-		t.Errorf("from %q expected error %s; got %s", s, err, err1)
-	}
-}
-
-// Check that we survive bad data.
-func TestBadData(t *testing.T) {
-	corruptDataCheck("", io.EOF, t)
-	corruptDataCheck("\x7Fhi", io.ErrUnexpectedEOF, t)
-	corruptDataCheck("\x03now is the time for all good men", errBadType, t)
-	// issue 6323.
-	corruptDataCheck("\x04\x24foo", errRange, t)
-}
-
 // Types not supported at top level by the Encoder.
 var unsupportedValues = []interface{}{
 	make(chan int),
@@ -955,30 +937,40 @@ func TestErrorForHugeSlice(t *testing.T) {
 	}
 }
 
-// Don't crash, just give error with corrupted length.
-// Issue 10270.
-func TestErrorBadDrop(t *testing.T) {
-	data := []byte{0x05, 0x10, 0x00, 0x28, 0x55, 0x7b, 0x02, 0x02, 0x7f, 0x83, 0x02}
-	d := NewDecoder(bytes.NewReader(data))
-	err := d.Decode(nil)
-	if err == nil {
-		t.Fatal("decode: no error")
-	}
-	if !strings.Contains(err.Error(), "interface encoding") {
-		t.Fatalf("decode: expected interface encoding error, got %s", err.Error())
-	}
+type badDataTest struct {
+	input string      // The input encoded as a hex string.
+	error string      // A substring of the error that should result.
+	data  interface{} // What to decode into.
 }
 
-// Don't crash, just give error with corrupted slice.
-// Issue 10273.
-func TestErrorBadSliceLength(t *testing.T) {
-	data := []byte{0x13, 0x0a, 0x00, 0xfb, 0x5d, 0xad, 0x0b, 0xf8, 0xff, 0x02, 0x02, 0x63, 0xe7, 0x00, 0x02, 0xfa, 0x28, 0x02, 0x02, 0x02, 0xa8, 0x98, 0x59}
-	d := NewDecoder(bytes.NewReader(data))
-	err := d.Decode(nil)
-	if err == nil {
-		t.Fatal("decode: no error")
-	}
-	if !strings.Contains(err.Error(), "slice length too large") {
-		t.Fatalf("decode: expected slice length too large error, got %s", err.Error())
+var badDataTests = []badDataTest{
+	{"", "EOF", nil},
+	{"7F6869", "unexpected EOF", nil},
+	{"036e6f77206973207468652074696d6520666f7220616c6c20676f6f64206d656e", "unknown type id", new(ET2)},
+	{"0424666f6f", "field numbers out of bounds", new(ET2)}, // Issue 6323.
+	{"05100028557b02027f8302", "interface encoding", nil},   // Issue 10270.
+	// Issue 10273.
+	{"130a00fb5dad0bf8ff020263e70002fa28020202a89859", "slice length too large", nil},
+	{"0f1000fb285d003316020735ff023a65c5", "interface encoding", nil},
+	{"03fffb0616fffc00f902ff02ff03bf005d02885802a311a8120228022c028ee7", "GobDecoder", nil},
+}
+
+// TestBadData tests that various problems caused by malformed input
+// are caught as errors and do not cause panics.
+func TestBadData(t *testing.T) {
+	for i, test := range badDataTests {
+		data, err := hex.DecodeString(test.input)
+		if err != nil {
+			t.Fatalf("#%d: hex error: %s", i, err)
+		}
+		d := NewDecoder(bytes.NewReader(data))
+		err = d.Decode(test.data)
+		if err == nil {
+			t.Errorf("decode: no error")
+			continue
+		}
+		if !strings.Contains(err.Error(), test.error) {
+			t.Errorf("#%d: decode: expected %q error, got %s", i, test.error, err.Error())
+		}
 	}
 }