archive/zip: Fix bounds check panic for ZIP files with a truncated extra header.

R=adg, dave
CC=gobot, golang-dev
https://golang.org/cl/6811080

src/pkg/archive/zip/reader.go

@@ -238,7 +238,7 @@ func readDirectoryHeader(f *File, r io.Reader) error {
 
 	if len(f.Extra) > 0 {
 		b := readBuf(f.Extra)
-		for len(b) > 0 {
+		for len(b) > 4 { // need at least tag and size
 			tag := b.uint16()
 			size := b.uint16()
 			if int(size) > len(b) {
@@ -259,6 +259,10 @@ func readDirectoryHeader(f *File, r io.Reader) error {
 			}
 			b = b[size:]
 		}
+		// Should have consumed the whole header.
+		if len(b) != 0 {
+			return ErrFormat
+		}
 	}
 	return nil
 }

src/pkg/archive/zip/zip_test.go

@@ -174,13 +174,31 @@ func TestZip64(t *testing.T) {
 	}
 }
 
-// Issue 4302.
-func TestInvalidExtraHedaer(t *testing.T) {
-	const timeFormat = "20060102T150405.000.txt"
-
+func testInvalidHeader(h *FileHeader, t *testing.T) {
 	var buf bytes.Buffer
 	z := NewWriter(&buf)
 
+	f, err := z.CreateHeader(h)
+	if err != nil {
+		t.Fatalf("error creating header: %v", err)
+	}
+	if _, err := f.Write([]byte("hi")); err != nil {
+		t.Fatalf("error writing content: %v", err)
+	}
+	if err := z.Close(); err != nil {
+		t.Fatal("error closing zip writer: %v", err)
+	}
+
+	b := buf.Bytes()
+	if _, err = NewReader(bytes.NewReader(b), int64(len(b))); err != ErrFormat {
+		t.Fatal("got %v, expected ErrFormat", err)
+	}
+}
+
+// Issue 4302.
+func TestHeaderInvalidTagAndSize(t *testing.T) {
+	const timeFormat = "20060102T150405.000.txt"
+
 	ts := time.Now()
 	filename := ts.Format(timeFormat)
 
@@ -191,19 +209,14 @@ func TestInvalidExtraHedaer(t *testing.T) {
 	}
 	h.SetModTime(ts)
 
-	fh, err := z.CreateHeader(&h)
-	if err != nil {
-		t.Fatalf("error creating header: %v", err)
-	}
-	if _, err := fh.Write([]byte("hi")); err != nil {
-		t.Fatalf("error writing content: %v", err)
-	}
-	if err := z.Close(); err != nil {
-		t.Fatal("error closing zip writer: %v", err)
-	}
+	testInvalidHeader(&h, t)
+}
 
-	b := buf.Bytes()
-	if _, err = NewReader(bytes.NewReader(b), int64(len(b))); err == nil {
-		t.Fatal("expected ErrFormat")
+func TestHeaderTooShort(t *testing.T) {
+	h := FileHeader{
+		Name:   "foo.txt",
+		Method: Deflate,
+		Extra:  []byte{zip64ExtraId}, // missing size
 	}
+	testInvalidHeader(&h, t)
 }