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gh-95778: Add pre-check for int-to-str conversion #96537

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Merged
gpshead merged 14 commits into from
Sep 4, 2022
Merged

gh-95778: Add pre-check for int-to-str conversion #96537

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2fbc9ce
Add pre-check for int-to-str conversion
mdickinson Sep 3, 2022
d16db91
Avoid potential undefined behaviour from overflow
mdickinson Sep 3, 2022
66a07ac
Reworked, even cruder bound, that avoids potential issues with intege…
mdickinson Sep 3, 2022
6eadbda
Rename the error message constants.
gpshead Sep 4, 2022
195686c
Add a DoS prevention success timed regression test.
gpshead Sep 4, 2022
87bd23d
Improve the test to check close to the limit.
gpshead Sep 4, 2022
de9ed4d
Use fewer digits in the test to speed it up on slow hosts.
gpshead Sep 4, 2022
dbd8da9
Misc: Fix a typo in the header comment.
gpshead Sep 4, 2022
c49a737
Change timers if process_time() returns 0. #wasm
gpshead Sep 4, 2022
35c5ea7
Merge branch 'main' into fix/int-to-str-dos
gpshead Sep 4, 2022
730915d
Update comment to suggest reading the PR for detail
gpshead Sep 4, 2022
56f08c2
Minor comment typo fix (restart CI).
gpshead Sep 4, 2022
4dae3e0
cleanup the test.
gpshead Sep 4, 2022
adb1784
Add Mark's name to the NEWS entry.
gpshead Sep 4, 2022
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Add a DoS prevention success timed regression test.
  • Loading branch information
@gpshead
gpshead committed Sep 4, 2022
commit 195686ca965a5097e4b22d4682e6938ad6baa7c1
72 changes: 72 additions & 0 deletions Lib/test/test_int.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import sys
import time

import unittest
from test import support
Expand Down Expand Up @@ -632,6 +633,77 @@ def test_max_str_digits(self):
with self.assertRaises(ValueError):
str(i)

def test_denial_of_service_prevented_int_to_str(self):
"""Regression test: ensure we fail before performing O(N**2) work."""
maxdigits = sys.get_int_max_str_digits()
assert maxdigits < 100_000, maxdigits # A test prerequisite.
process_time = time.process_time

huge_int = int(f'0x{"c"*100_000}', base=16) # 120412 decimal digits.
with support.adjust_int_max_str_digits(120_412):
start = process_time()
huge_decimal = str(huge_int)
seconds_to_convert = process_time() - start
self.assertEqual(len(huge_decimal), 120_412)
# Ensuring that we chose a slow enough conversion to time.
# Unlikely any CPU core will ever be faster than the assertion.
# It takes 0.25 seconds on a Zen based cloud VM in an opt build.
self.assertGreater(seconds_to_convert, 0.02,
msg="'We're gonna need a bigger boat (int).'")

with self.assertRaises(ValueError) as err:
start = process_time()
str(huge_int)
seconds_to_fail_huge = process_time() - start
self.assertIn('conversion', str(err.exception))
self.assertLess(seconds_to_fail_huge, seconds_to_convert/8)

# Now we test that a conversion that would take 30x as long also fails
# in a similarly fast fashion.
extra_huge_int = int(f'0x{"c"*500_000}', base=16) # 602060 digits.
with self.assertRaises(ValueError) as err:
start = process_time()
# If not limited, 8 seconds said Zen based cloud VM.
str(extra_huge_int)
seconds_to_fail_extra_huge = process_time() - start
self.assertIn('conversion', str(err.exception))
self.assertLess(seconds_to_fail_extra_huge, seconds_to_convert/8)

def test_denial_of_service_prevented_str_to_int(self):
"""Regression test: ensure we fail before performing O(N**2) work."""
maxdigits = sys.get_int_max_str_digits()
assert maxdigits < 100_000, maxdigits # A test prerequisite.
process_time = time.process_time

huge = '8'*200_000
with support.adjust_int_max_str_digits(200_000):
start = process_time()
int(huge)
seconds_to_convert = process_time() - start
# Ensuring that we chose a slow enough conversion to time.
# Unlikely any CPU core will ever be faster than the assertion.
# It takes 0.25 seconds on a Zen based cloud VM in an opt build.
self.assertGreater(seconds_to_convert, 0.02,
msg="'We're gonna need a bigger boat (str).'")

with self.assertRaises(ValueError) as err:
start = process_time()
int(huge)
seconds_to_fail_huge = process_time() - start
self.assertIn('conversion', str(err.exception))
self.assertLess(seconds_to_fail_huge, seconds_to_convert/8)

# Now we test that a conversion that would take 30x as long also fails
# in a similarly fast fashion.
extra_huge = '7'*1_200_000
with self.assertRaises(ValueError) as err:
start = process_time()
# If not limited, 8 seconds said Zen based cloud VM.
int(extra_huge)
seconds_to_fail_extra_huge = process_time() - start
self.assertIn('conversion', str(err.exception))
self.assertLess(seconds_to_fail_extra_huge, seconds_to_convert/8)

def test_power_of_two_bases_unlimited(self):
"""The limit does not apply to power of 2 bases."""
maxdigits = sys.get_int_max_str_digits()
Expand Down