encoding/gob: fix check for short input in slice decode
R=golang-dev, dsymonds, r, nigeltao
CC=golang-dev
https://golang.org/cl/6374059
diff --git a/src/pkg/encoding/gob/decode.go b/src/pkg/encoding/gob/decode.go
index e32a178..8690b35 100644
--- a/src/pkg/encoding/gob/decode.go
+++ b/src/pkg/encoding/gob/decode.go
@@ -562,6 +562,9 @@
func (dec *Decoder) decodeArrayHelper(state *decoderState, p uintptr, elemOp decOp, elemWid uintptr, length, elemIndir int, ovfl error) {
instr := &decInstr{elemOp, 0, elemIndir, 0, ovfl}
for i := 0; i < length; i++ {
+ if state.b.Len() == 0 {
+ errorf("decoding array or slice: length exceeds input size (%d elements)", length)
+ }
up := unsafe.Pointer(p)
if elemIndir > 1 {
up = decIndirect(up, elemIndir)
@@ -652,9 +655,6 @@
// Slices are encoded as an unsigned length followed by the elements.
func (dec *Decoder) decodeSlice(atyp reflect.Type, state *decoderState, p uintptr, elemOp decOp, elemWid uintptr, indir, elemIndir int, ovfl error) {
nr := state.decodeUint()
- if nr > uint64(state.b.Len()) {
- errorf("length of slice exceeds input size (%d elements)", nr)
- }
n := int(nr)
if indir > 0 {
up := unsafe.Pointer(p)
diff --git a/src/pkg/encoding/gob/encoder_test.go b/src/pkg/encoding/gob/encoder_test.go
index 35ca6ca..b684772 100644
--- a/src/pkg/encoding/gob/encoder_test.go
+++ b/src/pkg/encoding/gob/encoder_test.go
@@ -813,3 +813,32 @@
t.Errorf("expected error about no exported fields; got %v", err)
}
}
+
+// There was an error check comparing the length of the input with the
+// length of the slice being decoded. It was wrong because the next
+// thing in the input might be a type definition, which would lead to
+// an incorrect length check. This test reproduces the corner case.
+
+type Z struct {
+}
+
+func Test29ElementSlice(t *testing.T) {
+ Register(Z{})
+ src := make([]interface{}, 100) // Size needs to be bigger than size of type definition.
+ for i := range src {
+ src[i] = Z{}
+ }
+ buf := new(bytes.Buffer)
+ err := NewEncoder(buf).Encode(src)
+ if err != nil {
+ t.Fatalf("encode: %v", err)
+ return
+ }
+
+ var dst []interface{}
+ err = NewDecoder(buf).Decode(&dst)
+ if err != nil {
+ t.Errorf("decode: %v", err)
+ return
+ }
+}
