8000 [3.6] bpo-39017: Avoid infinite loop in the tarfile module (GH-21454) by miss-islington · Pull Request #21485 · python/cpython · GitHub
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[3.6] 8000 bpo-39017: Avoid infinite loop in the tarfile module (GH-21454) #21485

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Merged
merged 1 commit into from
Jul 15, 2020
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[3.6] bpo-39017: Avoid infinite loop in the tarfile module (GH-21454) #21485

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2 changes: 2 additions & 0 deletions Lib/tarfile.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1231,6 +1231,8 @@ 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]

# Normally, we could just use "utf-8" as the encoding and "strict"
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Binary file added Lib/test/recursion.tar
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7 changes: 7 additions & 0 deletions Lib/test/test_tarfile.py
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Expand Up @@ -395,6 +395,13 @@ def test_premature_end_of_archive(self):
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
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2020-07-12-22-16-58.bpo-39017.x3Cg-9.rst
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@@ -0,0 +1 @@
Avoid infinite loop when reading specially crafted TAR files using the tarfile module (CVE-2019-20907).
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