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bpo-45509: Check gzip headers for corrupted fields #29028

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Merged
serhiy-storchaka merged 12 commits into from
May 13, 2026
Merged

bpo-45509: Check gzip headers for corrupted fields #29028

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617e064
Check gzip headers for corrupted fields
rhpvorderman Oct 18, 2021
3d5bb47
Minor performance tweaks to _read_gzip_header
rhpvorderman Nov 24, 2021
e68e76e
Optimize _read_gzip_header for the most common code paths
rhpvorderman Nov 24, 2021
2dfc96c
Merge branch 'main' into bpo-45509
hauntsaninja Jan 30, 2023
65108b6
Merge branch 'main' into bpo-45509
rhpvorderman Apr 10, 2026
64ad8e9
Update test_gzip.py
rhpvorderman Apr 10, 2026
a8fe591
Merge branch 'main' into bpo-45509
serhiy-storchaka May 11, 2026
4d13ece
Factor out reading until null and use a bytearray
rhpvorderman May 12, 2026
6ea0f0e
Simplify comments. Better grouping of statements
rhpvorderman May 12, 2026
4d0f01d
Fix error in method
rhpvorderman May 12, 2026
2fb1ce0
Do not store header for common FNAME flag
rhpvorderman May 13, 2026
ae60e94
Reduce number of object creations
rhpvorderman May 13, 2026
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Reduce number of object creations
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@rhpvorderman
rhpvorderman committed May 13, 2026
commit ae60e940781ff5f6fc576fc0b07de331d677c7e3
18 changes: 7 additions & 11 deletions Lib/gzip.py
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Original file line number Diff line number Diff line change
Expand Up @@ -484,18 +484,14 @@ def _read_exact(fp, n):
return data


def _read_until_null(fp):
'''Read until the first encountered null byte in fp'''
result = io.BytesIO()
def _read_until_null(fp, append_to):
'''Read until the first encountered null byte in fp.
Append to given byte array object'''
while True:
s = fp.read(1)
if not s:
raise EOFError("Compressed file ended before the "
"end-of-stream marker was reached")
result.write(s)
if s == b'\000':
append_to += s
if not s or s == b'\000':
break
return result.getvalue()


def _read_gzip_header(fp):
Expand Down Expand Up @@ -535,9 +531,9 @@ def _read_gzip_header(fp):
header += extra_len_bytes
header += _read_exact(fp, extra_len)
if flag & FNAME:
header += _read_until_null(fp)
_read_until_null(fp, append_to=header)
if flag & FCOMMENT:
header += _read_until_null(fp)
_read_until_null(fp, append_to=header)
if flag & FHCRC:
# Header CRC is the last 16 bits of a crc32.
header_crc, = struct.unpack("<H", _read_exact(fp, 2))
Expand Down
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