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
@@ -1249,6 +1249,8 @@ 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]
# Normally, we could just use "utf-8" as the encoding and "strict"
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -429,6 +429,13 @@ class CommonReadTest(ReadTest):
with self.assertRaisesRegex(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.assertRaisesRegex(tarfile.ReadError, "file could not be opened successfully"):
+ with tarfile.open(support.findfile('recursion.tar')) as tar:
+ pass
+
class MiscReadTestBase(CommonReadTest):
def requires_name_attribute(self):
pass
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-07-12-22-16-58.bpo-39017.x3Cg-9.rst
@@ -0,0 +1 @@
+Avoid infinite loop when reading specially crafted TAR files using the tarfile module (CVE-2019-20907).
--- /dev/null
+++ b/Lib/test/recursion.tar.asc
@@ -0,0 +1,10 @@
+YmNhbGxlcgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADAAAAAAAAAAMAAAAAAA
+AAAwAAAAAAAAADEAAAAAAAAAAAAAADAAAAAAAAAAAAAAADAwMjc1NQAgZwAAAAAAAAAAAAAAAAAA
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAwMAAAAAAAAAAAAAAAAAAAAAAAAAAA
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAwAAAAAAAAADAAAAAA
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAw
+IFg9