gh-157265: Honor None result of filter for link fallbacks by encukou · Pull Request #157266 · python/cpython

encukou · 2026-09-10T11:48:20Z

Issue: tarfile hardlink fallback ignores custom extraction filter rejection via None #157265

Co-authored-by: Stan Ulbrych <stan@python.org>

miss-islington-app · 2026-09-11T12:20:19Z

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

miss-islington-app · 2026-09-11T12:20:19Z

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

miss-islington-app · 2026-09-11T12:20:19Z

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

miss-islington-app · 2026-09-11T12:20:20Z

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

miss-islington-app · 2026-09-11T12:20:20Z

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

miss-islington-app · 2026-09-11T12:20:20Z

Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

bedevere-app · 2026-09-11T12:20:38Z

GH-157304 is a backport of this pull request to the 3.10 branch.

bedevere-app · 2026-09-11T12:20:45Z

GH-157305 is a backport of this pull request to the 3.12 branch.

bedevere-app · 2026-09-11T12:20:49Z

GH-157306 is a backport of this pull request to the 3.11 branch.

bedevere-app · 2026-09-11T12:20:56Z

GH-157307 is a backport of this pull request to the 3.14 branch.

bedevere-app · 2026-09-11T12:21:01Z

GH-157308 is a backport of this pull request to the 3.13 branch.

bedevere-app · 2026-09-11T12:21:19Z

GH-157309 is a backport of this pull request to the 3.15 branch.

bedevere-bot · 2026-09-11T12:41:48Z

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Debian root 3.x (tier-1) has failed when building commit fb2f0bb.

What do you need to do:

Don't panic.
Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/345/builds/15324) and take a look at the build logs.
Check if the failure is related to this commit (fb2f0bb) or if it is a false positive.
If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/345/builds/15324

Failed tests:

test.test_multiprocessing_fork.test_processes

Failed subtests:

test_interrupt - test.test_multiprocessing_fork.test_processes.WithProcessesTestProcess.test_interrupt

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/contextlib.py", line 116, in inner
    return func(*args, **kwds)
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/_test_multiprocessing.py", line 651, in test_interrupt
    exitcode = self._kill_process(multiprocessing.Process.interrupt)
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/contextlib.py", line 116, in inner
    return func(*args, **kwds)
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/_test_multiprocessing.py", line 632, in _kill_process
    self.assertEqual(join(), None)
                     ~~~~^^
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/_test_multiprocessing.py", line 305, in __call__
    return self.func(*args, **kwds)
           ~~~~~~~~~^^^^^^^^^^^^^^^
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/multiprocessing/process.py", line 156, in join
    res = self._popen.wait(timeout)
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/multiprocessing/popen_fork.py", line 44, in wait
    return self.poll(os.WNOHANG if timeout == 0.0 else 0)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/multiprocessing/popen_fork.py", line 28, in poll
    pid, sts = os.waitpid(self.pid, flag)
               ~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/_test_multiprocessing.py", line 628, in handler
    raise RuntimeError('join took too long: %s' % p)
RuntimeError: join took too long: <Process name='Process-1' pid=3460618 parent=3460616 started daemon>


Traceback (most recent call last):
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/contextlib.py", line 116, in inner
    return func(*args, **kwds)
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/_test_multiprocessing.py", line 651, in test_interrupt
    exitcode = self._kill_process(multiprocessing.Process.interrupt)
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/contextlib.py", line 116, in inner
    return func(*args, **kwds)
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/_test_multiprocessing.py", line 632, in _kill_process
    self.assertEqual(join(), None)
                     ~~~~^^
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/_test_multiprocessing.py", line 305, in __call__
    return self.func(*args, **kwds)
           ~~~~~~~~~^^^^^^^^^^^^^^^
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/multiprocessing/process.py", line 156, in join
    res = self._popen.wait(timeout)
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/multiprocessing/popen_fork.py", line 44, in wait
    return self.poll(os.WNOHANG if timeout == 0.0 else 0)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/multiprocessing/popen_fork.py", line 28, in poll
    pid, sts = os.waitpid(self.pid, flag)
               ~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/_test_multiprocessing.py", line 628, in handler
    raise RuntimeError('join took too long: %s' % p)
RuntimeError: join took too long: <Process name='Process-171' pid=3439307 parent=3438815 started daemon>

bedevere-bot · 2026-09-11T12:42:54Z

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 Windows 3.x (tier-2) has failed when building commit fb2f0bb.

What do you need to do:

Don't panic.
Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/729/builds/11241) and take a look at the build logs.
Check if the failure is related to this commit (fb2f0bb) or if it is a false positive.
If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/729/builds/11241

Failed tests:

test_tarfile

Failed subtests:

test_sneaky_hardlink_fallback - test.test_tarfile.TestExtractionFilters.test_sneaky_hardlink_fallback

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "C:\Users\buildworker\buildarea\3.x.ware-win11-arm64\build\Lib\test\test_tarfile.py", line 4625, in test_sneaky_hardlink_fallback
    self.expect_exception(
    ~~~~~~~~~~~~~~~~~~~~~^
        tarfile.LinkFallbackError,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
        "link 'boom' would be extracted as a copy of "
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        + "'c/escape', which was rejected")
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\buildworker\buildarea\3.x.ware-win11-arm64\build\Lib\test\test_tarfile.py", line 4099, in expect_exception
    with self.assertRaisesRegex(exc_type, message_re):
         ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
AssertionError: LinkFallbackError not raised

bedevere-bot · 2026-09-11T12:54:31Z

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows11 Non-Debug 3.x (tier-1) has failed when building commit fb2f0bb.

What do you need to do:

Don't panic.
Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/914/builds/6095) and take a look at the build logs.
Check if the failure is related to this commit (fb2f0bb) or if it is a false positive.
If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/914/builds/6095

Failed tests:

test_tarfile

Failed subtests:

test_sneaky_hardlink_fallback - test.test_tarfile.TestExtractionFilters.test_sneaky_hardlink_fallback

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "b:\uildarea\3.x.ware-win11.nondebug\build\Lib\test\test_tarfile.py", line 4625, in test_sneaky_hardlink_fallback
    self.expect_exception(
    ~~~~~~~~~~~~~~~~~~~~~^
        tarfile.LinkFallbackError,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
        "link 'boom' would be extracted as a copy of "
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        + "'c/escape', which was rejected")
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "b:\uildarea\3.x.ware-win11.nondebug\build\Lib\test\test_tarfile.py", line 4099, in expect_exception
    with self.assertRaisesRegex(exc_type, message_re):
         ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
AssertionError: LinkFallbackError not raised

gh-157266: Adjust test for Windows On Windows (no symlinks, no hardlinks), the behaviour is the same as without the fix in GH-157266: - a/t/dummy is extracted - b/ is extracted - c/ is *not* created (the target, a/t, is not in the archive) - c/escape: c/ is created; escape is skipped (target, c/../../link_here, is not in archive) - c is not recreated as a directory - boom is not created (target is c/escape, which falls back to ..\..\link_here, which does not exist in archive)

…cks (pythonGH-157266) Co-authored-by: Stan Ulbrych <stan@python.org>

pythongh-157266: Adjust test for Windows On Windows (no symlinks, no hardlinks), the behaviour is the same as without the fix in pythonGH-157266: - a/t/dummy is extracted - b/ is extracted - c/ is *not* created (the target, a/t, is not in the archive) - c/escape: c/ is created; escape is skipped (target, c/../../link_here, is not in archive) - c is not recreated as a directory - boom is not created (target is c/escape, which falls back to ..\..\link_here, which does not exist in archive)

…cks (pythonGH-157266) Co-authored-by: Stan Ulbrych <stan@python.org>

pythongh-157266: Adjust test for Windows On Windows (no symlinks, no hardlinks), the behaviour is the same as without the fix in pythonGH-157266: - a/t/dummy is extracted - b/ is extracted - c/ is *not* created (the target, a/t, is not in the archive) - c/escape: c/ is created; escape is skipped (target, c/../../link_here, is not in archive) - c is not recreated as a directory - boom is not created (target is c/escape, which falls back to ..\..\link_here, which does not exist in archive)

CVE-2026-87910 / PSF-2026-40 (Medium): when tarfile cannot create a link and falls back to extracting the linked member as a copy, the extraction filter is consulted twice — once with the member's name replaced by the link's location, once under its own name. The first call's None (explicit rejection) was discarded, so a member a filter refused to see materialised at the link's location anyway (alert #8273, Grype, python 3.14.7 binary). The fix is merged upstream (python/cpython#157266, commit fb2f0bbc) but no released 3.14 image carries it. Following the established CVE-2026-15310 zipfile-backport pattern: - scripts/patch_cpython_tarfile_cve_2026_87910.py applies the reviewed 4-line pure-Python fix to the stdlib in builder-base and ldr (both stages build from the fresh base image), fails closed on source drift, and verifies at build time by reproducing the vulnerable fallback: a filter that allows secret.txt under its own name but rejects it under the hardlink's must leave nothing at the link's location. Verified against pristine 3.14.7: unpatched the copy materialises, patched it does not; ordinary hardlink extraction unaffected. - .grype.yaml: fix-state-unknown binary-CPE entry with the same removal condition as the zipfile backport (fixed 3.14 image ships). - tests/deployment/test_cpython_tarfile_backport.py: contract tests for hunk application, idempotency, drift refusal, plus the behavioral property on the image's 3.14 stdlib (skipped on the 3.12 dev venv, which predates this project's image scope). Resolves #8273.

…acks (GH-157266) (GH-157308) (cherry picked from commit fb2f0bb) Also includes commit d9565e5: gh-157266: Adjust test for Windows (GH-157334) Co-authored-by: Petr Viktorin <encukou@gmail.com> Co-authored-by: Stan Ulbrych <stan@python.org>

- Dockerfile: correct the tarfile CVE comment — the upstream fix is merged on CPython main (python/cpython#157266, fb2f0bbc), not the 3.14 maintenance branch; the 3.14 backport (python/cpython#157307) is open. - test_cpython_tarfile_backport.py: skip the behavioral test based on whether the ambient tarfile actually carries the patch markers, not a version check plus two strings every 3.14.x contains; fix the module docstring's stale wording. - test_cpython_tarfile_backport.py: make the source-level test reject the variant that captures the first filter result but overwrites it before the None check, by asserting on the exact upstream hunk structure instead of marker presence plus a call count. - patch_cpython_tarfile_cve_2026_87910.py: print a clear notice (exit 0) when the target's tarfile already contains the fix; extend verify_runtime to exercise the accepted fallback-copy path, which the existing benign check never enters.

encukou and others added 3 commits September 10, 2026 13:39

Honor None result of filter for link fallbacks

3d66a90

Apply review suggestions

5c3e146

Co-authored-by: Stan Ulbrych <stan@python.org>

Add NEWS file

aebd409

encukou requested a review from ethanfurman as a code owner September 10, 2026 11:48

bedevere-app Bot mentioned this pull request Sep 10, 2026

tarfile hardlink fallback ignores custom extraction filter rejection via None #157265

Open

bedevere-app Bot added the awaiting core review label Sep 10, 2026

StanFromIreland approved these changes Sep 10, 2026

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bedevere-app Bot added awaiting merge and removed awaiting core review labels Sep 10, 2026

encukou merged commit fb2f0bb into python:main Sep 11, 2026
60 checks passed

bedevere-app Bot removed the awaiting merge label Sep 11, 2026

encukou deleted the tarfile-hardlink-none branch September 11, 2026 12:19

bedevere-app Bot removed the needs backport to 3.10 only security fixes label Sep 11, 2026

bedevere-app Bot removed the needs backport to 3.12 only security fixes label Sep 11, 2026

bedevere-app Bot removed the needs backport to 3.11 only security fixes label Sep 11, 2026

bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Sep 11, 2026

bedevere-app Bot removed the needs backport to 3.13 bugs and security fixes label Sep 11, 2026

bedevere-app Bot removed the needs backport to 3.15 pre-release feature fixes, bugs and security fixes label Sep 11, 2026

encukou mentioned this pull request Sep 11, 2026

gh-157265: Adjust test for Windows #157334

Merged

clin1234 pushed a commit to clin1234/cpython that referenced this pull request Sep 12, 2026

pythongh-157265: tarfile: Honor None result of filter for link fallba…

4cbdc6a

…cks (pythonGH-157266) Co-authored-by: Stan Ulbrych <stan@python.org>

johnslavik pushed a commit to johnslavik/cpython that referenced this pull request Sep 14, 2026

pythongh-157265: tarfile: Honor None result of filter for link fallba…

28583e6

…cks (pythonGH-157266) Co-authored-by: Stan Ulbrych <stan@python.org>

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encukou commented Sep 10, 2026 •

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