From e8efbb448a26b37d511a697c272b71fbad41fe77 Mon Sep 17 00:00:00 2001
From: Jeremy Paige <ucodery@gmail.com>
Date: Tue, 3 Nov 2020 13:26:57 -0800
Subject: [PATCH] Address CVE-2019-20907 in tarfile module

---
 Lib/tarfile.py           |   2 ++
 Lib/test/recursion.tar   | Bin 0 -> 516 bytes
 Lib/test/test_tarfile.py |   7 +++++++
 3 files changed, 9 insertions(+)
 create mode 100644 Lib/test/recursion.tar

diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index adf91d53823bb5..574a6bb279ddf0 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -1400,6 +1400,8 @@ def _proc_pax(self, tarfile):
 
             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")
diff --git a/Lib/test/recursion.tar b/Lib/test/recursion.tar
new file mode 100644
index 0000000000000000000000000000000000000000..b8237251964983f54ed1966297e887636cd0c5f4
GIT binary patch
literal 516
zcmYdFPRz+kEn=W0Fn}74P8%Xw3X=l~85kIuo0>8xq$A1Gm}!7)KUsFc41m#O8A5+e
I1_}|j06>QaCIA2c

literal 0
HcmV?d00001

diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index 89bd738aea0da2..b7ff47f783e72e 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -321,6 +321,13 @@ def test_premature_end_of_archive(self):
                 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