compress/zlib: detect truncated streams

Reader failed to detect truncated streams since calls to
io.ReadFull did not check if the error is io.EOF.

Change-Id: I86c497519daaaccefc6eb5617ddcd8fd3b99f51b
Reviewed-on: https://go-review.googlesource.com/14835Reviewed-by: Nigel Tao <nigeltao@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/compress/zlib/reader.go

@@ -101,6 +101,9 @@ func (z *reader) Read(p []byte) (n int, err error) {
 
 	// Finished file; check checksum.
 	if _, err := io.ReadFull(z.r, z.scratch[0:4]); err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
 		z.err = err
 		return 0, err
 	}
@@ -130,6 +133,9 @@ func (z *reader) Reset(r io.Reader, dict []byte) error {
 	}
 	_, err := io.ReadFull(z.r, z.scratch[0:2])
 	if err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
 		return err
 	}
 	h := uint(z.scratch[0])<<8 | uint(z.scratch[1])
@@ -140,6 +146,9 @@ func (z *reader) Reset(r io.Reader, dict []byte) error {
 	if haveDict {
 		_, err = io.ReadFull(z.r, z.scratch[0:4])
 		if err != nil {
+			if err == io.EOF {
+				err = io.ErrUnexpectedEOF
+			}
 			return err
 		}
 		checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3])

src/compress/zlib/reader_test.go

@@ -22,6 +22,30 @@ type zlibTest struct {
 // http://www.zlib.net/zpipe.c
 
 var zlibTests = []zlibTest{
+	{
+		"truncated empty",
+		"",
+		[]byte{},
+		nil,
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"truncated dict",
+		"",
+		[]byte{0x78, 0xbb},
+		[]byte{0x00},
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"truncated checksum",
+		"",
+		[]byte{0x78, 0xbb, 0x00, 0x01, 0x00, 0x01, 0xca, 0x48,
+			0xcd, 0xc9, 0xc9, 0xd7, 0x51, 0x28, 0xcf, 0x2f,
+			0xca, 0x49, 0x01, 0x04, 0x00, 0x00, 0xff, 0xff,
+		},
+		[]byte{0x00},
+		io.ErrUnexpectedEOF,
+	},
 	{
 		"empty",
 		"",