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bpo-45507: Throw EOF error when gzip headers or trailers are truncated #29023

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bpo-45507: Throw EOF error when gzip headers or trailers are truncated #29023

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83e58a2
Throw EOF error when trailer is not present in gzip member
rhpvorderman Oct 18, 2021
773c4f1
Fix bug where missing NAME or COMMENt fields do not trigger an error
rhpvorderman Oct 18, 2021
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Fix bug where missing NAME or COMMENt fields do not trigger an error
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@rhpvorderman
rhpvorderman committed Oct 18, 2021
commit 773c4f173f2a237d20727c0b78aa4f8233796865
8 changes: 4 additions & 4 deletions Lib/gzip.py
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Original file line number Diff line number Diff line change
Expand Up @@ -442,14 +442,14 @@ def _read_gzip_header(fp):
if flag & FNAME:
# Read and discard a null-terminated string containing the filename
while True:
s = fp.read(1)
if not s or s==b'\000':
s = _read_exact(fp, 1)
if s == b'\000':
break
if flag & FCOMMENT:
# Read and discard a null-terminated string containing a comment
while True:
s = fp.read(1)
if not s or s==b'\000':
s = _read_exact(fp, 1)
if s == b'\000':
break
if flag & FHCRC:
_read_exact(fp, 2) # Read & discard the 16-bit header CRC
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5 changes: 3 additions & 2 deletions Lib/test/test_gzip.py
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Expand Up @@ -562,7 +562,7 @@ def test_decompress(self):
datac = gzip.compress(data)
self.assertEqual(gzip.decompress(datac), data)

def test_decompress_uncompressed_header(self):
def test_truncated_header(self):
truncated_headers = [
b"\x1f\x8b\x08\x00\x00\x00\x00\x00\x00", # Missing OS byte
b"\x1f\x8b\x08\x02\x00\x00\x00\x00\x00\xff", # FHRC, but no checksum
Expand All @@ -573,7 +573,8 @@ def test_decompress_uncompressed_header(self):
]
for header in truncated_headers:
with self.subTest(header=header):
self.assertRaises(EOFError, gzip.decompress, header)
self.assertRaises(EOFError, gzip._read_gzip_header,
io.BytesIO(header))

def test_read_truncated(self):
data = data1*50
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5 changes: 3 additions & 2 deletions Misc/NEWS.d/next/Library/2021-10-18-11-20-24.bpo-45507.vWx2yS.rst
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@@ -1,2 +1,3 @@
Add regression tests for errors that are thrown when decompressing with the
``gzip`` module to ensure backwards-compatibility between Python versions.
Make sure EOFerror is thrown when gzip headers have missing or truncated
NAME or COMMENT fields when FNAME or FCOMMENT flags are set.