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gh-136065: Fix quadratic complexity in os.path.expandvars() (GH-134952)

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Co-authored-by: Łukasz Langa <lukasz@langa.pl>
This commit is contained in:
Serhiy Storchaka 2025-10-31 15:49:51 +02:00 • committed by GitHub
parent 81cec22a9b
commit f029e8db62
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GPG key ID: B5690EEEBB952194
5 changed files with 96 additions and 116 deletions
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126
Lib/ntpath.py
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@ -400,17 +400,23 @@ def expanduser(path):
# XXX With COMMAND.COM you can use any characters in a variable name,
# XXX except '^|<>='.
_varpattern = r"'[^']*'?|%(%|[^%]*%?)|\$(\$|[-\w]+|\{[^}]*\}?)"
_varsub = None
_varsubb = None
def expandvars(path):
"""Expand shell variables of the forms $var, ${var} and %var%.
Unknown variables are left unchanged."""
path = os.fspath(path)
global _varsub, _varsubb
if isinstance(path, bytes):
if b'$' not in path and b'%' not in path:
return path
import string
varchars = bytes(string.ascii_letters + string.digits + '_-', 'ascii')
quote = b'\''
if not _varsubb:
import re
_varsubb = re.compile(_varpattern.encode(), re.ASCII).sub
sub = _varsubb
percent = b'%'
brace = b'{'
rbrace = b'}'
@ -419,94 +425,44 @@ def expandvars(path):
else:
if '$' not in path and '%' not in path:
return path
import string
varchars = string.ascii_letters + string.digits + '_-'
quote = '\''
if not _varsub:
import re
_varsub = re.compile(_varpattern, re.ASCII).sub
sub = _varsub
percent = '%'
brace = '{'
rbrace = '}'
dollar = '$'
environ = os.environ
res = path[:0]
index = 0
pathlen = len(path)
while index < pathlen:
c = path[index:index+1]
if c == quote: # no expansion within single quotes
path = path[index + 1:]
pathlen = len(path)
try:
index = path.index(c)
res += c + path[:index + 1]
except ValueError:
res += c + path
index = pathlen - 1
elif c == percent: # variable or '%'
if path[index + 1:index + 2] == percent:
res += c
index += 1
else:
path = path[index+1:]
pathlen = len(path)
try:
index = path.index(percent)
except ValueError:
res += percent + path
index = pathlen - 1
else:
var = path[:index]
try:
if environ is None:
value = os.fsencode(os.environ[os.fsdecode(var)])
else:
value = environ[var]
except KeyError:
value = percent + var + percent
res += value
elif c == dollar: # variable or '$$'
if path[index + 1:index + 2] == dollar:
res += c
index += 1
elif path[index + 1:index + 2] == brace:
path = path[index+2:]
pathlen = len(path)
try:
index = path.index(rbrace)
except ValueError:
res += dollar + brace + path
index = pathlen - 1
else:
var = path[:index]
try:
if environ is None:
value = os.fsencode(os.environ[os.fsdecode(var)])
else:
value = environ[var]
except KeyError:
value = dollar + brace + var + rbrace
res += value
else:
var = path[:0]
index += 1
c = path[index:index + 1]
while c and c in varchars:
var += c
index += 1
c = path[index:index + 1]
try:
if environ is None:
value = os.fsencode(os.environ[os.fsdecode(var)])
else:
value = environ[var]
except KeyError:
value = dollar + var
res += value
if c:
index -= 1
def repl(m):
lastindex = m.lastindex
if lastindex is None:
return m[0]
name = m[lastindex]
if lastindex == 1:
if name == percent:
return name
if not name.endswith(percent):
return m[0]
name = name[:-1]
else:
res += c
index += 1
return res
if name == dollar:
return name
if name.startswith(brace):
if not name.endswith(rbrace):
return m[0]
name = name[1:-1]
try:
if environ is None:
return os.fsencode(os.environ[os.fsdecode(name)])
else:
return environ[name]
except KeyError:
return m[0]
return sub(repl, path)
# Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A\B.