[release-branch.go1.15] archive/zip: only preallocate File slice if reasonably sized

Since the number of files in the EOCD record isn't validated, it isn't
safe to preallocate Reader.Files using that field. A malformed archive
can indicate it contains up to 1 << 128 - 1 files. We can still safely
preallocate the slice by checking if the specified number of files in
the archive is reasonable, given the size of the archive.

Thanks to the OSS-Fuzz project for discovering this issue and to
Emmanuel Odeke for reporting it.

Updates #46242
Fixes #46396
Fixes CVE-2021-33196

Change-Id: I3c76d8eec178468b380d87fdb4a3f2cb06f0ee76
Reviewed-on: https://go-review.googlesource.com/c/go/+/318909
Trust: Roland Shoemaker <roland@golang.org>
Trust: Katie Hockman <katie@golang.org>
Trust: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
(cherry picked from commit 74242baa4136c7a9132a8ccd9881354442788c8c)
Reviewed-on: https://go-review.googlesource.com/c/go/+/322949
Reviewed-by: Filippo Valsorda <filippo@golang.org>

diff --git a/src/archive/zip/reader.go b/src/archive/zip/reader.go
index 13ff9ddcf42cc33b36484429652526612fa2887c..2d5151af3da39b769e4c13832cad36232534d1d8 100644 (file)
--- a/src/archive/zip/reader.go
+++ b/src/archive/zip/reader.go
@@ -84,7 +84,15 @@ func (z *Reader) init(r io.ReaderAt, size int64) error {
                return err
        }
        z.r = r
-       z.File = make([]*File, 0, end.directoryRecords)
+       // Since the number of directory records is not validated, it is not
+       // safe to preallocate z.File without first checking that the specified
+       // number of files is reasonable, since a malformed archive may
+       // indicate it contains up to 1 << 128 - 1 files. Since each file has a
+       // header which will be _at least_ 30 bytes we can safely preallocate
+       // if (data size / 30) >= end.directoryRecords.
+       if (uint64(size)-end.directorySize)/30 >= end.directoryRecords {
+               z.File = make([]*File, 0, end.directoryRecords)
+       }
        z.Comment = end.comment
        rs := io.NewSectionReader(r, 0, size)
        if _, err = rs.Seek(int64(end.directoryOffset), io.SeekStart); err != nil {

diff --git a/src/archive/zip/reader_test.go b/src/archive/zip/reader_test.go
index adca87a8b3829c7675145364c84145b7ea7aa4f6..6f67d2e4a9415d9400a0a0ea179698b528d0b8aa 100644 (file)
--- a/src/archive/zip/reader_test.go
+++ b/src/archive/zip/reader_test.go
@@ -1070,3 +1070,62 @@ func TestIssue12449(t *testing.T) {
                t.Errorf("Error reading the archive: %v", err)
        }
 }
+
+func TestCVE202133196(t *testing.T) {
+       // Archive that indicates it has 1 << 128 -1 files,
+       // this would previously cause a panic due to attempting
+       // to allocate a slice with 1 << 128 -1 elements.
+       data := []byte{
+               0x50, 0x4b, 0x03, 0x04, 0x14, 0x00, 0x08, 0x08,
+               0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x01, 0x02,
+               0x03, 0x62, 0x61, 0x65, 0x03, 0x04, 0x00, 0x00,
+               0xff, 0xff, 0x50, 0x4b, 0x07, 0x08, 0xbe, 0x20,
+               0x5c, 0x6c, 0x09, 0x00, 0x00, 0x00, 0x03, 0x00,
+               0x00, 0x00, 0x50, 0x4b, 0x01, 0x02, 0x14, 0x00,
+               0x14, 0x00, 0x08, 0x08, 0x08, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0xbe, 0x20, 0x5c, 0x6c, 0x09, 0x00,
+               0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x03, 0x00,
+               0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+               0x01, 0x02, 0x03, 0x50, 0x4b, 0x06, 0x06, 0x2c,
+               0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x2d,
+               0x00, 0x2d, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff, 0xff,
+               0xff, 0xff, 0xff, 0x31, 0x00, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0x00, 0x50, 0x4b, 0x06, 0x07, 0x00,
+               0x00, 0x00, 0x00, 0x6b, 0x00, 0x00, 0x00, 0x00,
+               0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x50,
+               0x4b, 0x05, 0x06, 0x00, 0x00, 0x00, 0x00, 0xff,
+               0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+               0xff, 0xff, 0xff, 0x00, 0x00,
+       }
+       _, err := NewReader(bytes.NewReader(data), int64(len(data)))
+       if err != ErrFormat {
+               t.Fatalf("unexpected error, got: %v, want: %v", err, ErrFormat)
+       }
+
+       // Also check that an archive containing a handful of empty
+       // files doesn't cause an issue
+       b := bytes.NewBuffer(nil)
+       w := NewWriter(b)
+       for i := 0; i < 5; i++ {
+               _, err := w.Create("")
+               if err != nil {
+                       t.Fatalf("Writer.Create failed: %s", err)
+               }
+       }
+       if err := w.Close(); err != nil {
+               t.Fatalf("Writer.Close failed: %s", err)
+       }
+       r, err := NewReader(bytes.NewReader(b.Bytes()), int64(b.Len()))
+       if err != nil {
+               t.Fatalf("NewReader failed: %s", err)
+       }
+       if len(r.File) != 5 {
+               t.Errorf("Archive has unexpected number of files, got %d, want 5", len(r.File))
+       }
+}