From 1fa6ef2bc7cee1c8e088dd8b397d9b2d54036dbc Mon Sep 17 00:00:00 2001

From: Rajarishi Devarajan <rishi93dev@gmail.com>

Date: Sun, 12 Jul 2020 23:47:42 +0200

Subject: [PATCH 1/4] bpo-39017 Fix infinite loop in the tarfile module

​

Add a check for length = 0 in the _proc_pax function to avoid running into an infinite loop

---

 Lib/tarfile.py           |   2 ++

 Lib/test/test_tarfile.py |   5 +++++

 3 files changed, 7 insertions(+)

 create mode 100644 Lib/test/recursion.tar

​

--- a/Lib/tarfile.py

+++ b/Lib/tarfile.py

@@ -1400,6 +1400,8 @@ class TarInfo(object):

             length, keyword = match.groups()

             length = int(length)

+            if length == 0:

+                raise InvalidHeaderError("invalid header")

             value = buf[match.end(2) + 1:match.start(1) + length - 1]

             keyword = keyword.decode("utf8")

--- a/Lib/test/test_tarfile.py

+++ b/Lib/test/test_tarfile.py

@@ -321,6 +321,14 @@ class CommonReadTest(ReadTest):

                 with self.assertRaisesRegexp(tarfile.ReadError, "unexpected end of data"):

                     tar.extractfile(t).read()

+    def test_length_zero_header(self):

+        # bpo-39017 (CVE-2019-20907): reading a zero-length header should fail

+        # with an exception

+        with self.assertRaisesRegexp(tarfile.ReadError, "file could not be opened successfully"):

+            with tarfile.open(support.findfile('recursion.tar')) as tar:

+                pass

+

+

 class MiscReadTest(CommonReadTest):

     taropen = tarfile.TarFile.taropen

​