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gh-151284: Fix test_capi on UBSan#151286

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vstinner:test_capi
Jun 11, 2026
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gh-151284: Fix test_capi on UBSan#151286
vstinner merged 2 commits into
python:mainfrom
vstinner:test_capi

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@vstinner vstinner commented Jun 10, 2026 •
edited by bedevere-app Bot
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Remove two checks relying on undefined behavior in test_fromwidechar() of test_capi.

Enable test_capi in GitHub Action "Reusable Sanitizer".

@vstinner
pythongh-151284: Fix test_capi on UBSan
72de4e6 
Remove two checks relying on undefined behavior in
test_fromwidechar() of test_capi.

Enable test_capi in GitHub Action "Reusable Sanitizer".
@vstinner vstinner added skip news needs backport to 3.13 bugs and security fixes needs backport to 3.14 bugs and security fixes needs backport to 3.15 pre-release feature fixes, bugs and security fixes labels Jun 10, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Jun 10, 2026
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@vstinner

vstinner commented Jun 10, 2026

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PyObject *
PyUnicode_FromWideChar(const wchar_t *u, Py_ssize_t size)
{
    ...

    if (find_maxchar_surrogates(u, u + size,
                                &maxchar, &num_surrogates) == -1)
        return NULL;

    ...
}

u + size with size=PY_SSIZE_T_MAX triggers an undefined behavior.

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vstinner commented Jun 10, 2026

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@serhiy-storchaka: Would you mind to review this change?

serhiy-storchaka
serhiy-storchaka reviewed Jun 11, 2026
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I think we should left commented out calls with an explanatory comment, like for crashes. It indicates that we did not miss these cases, so they will not be reintroduced.

@vstinner

vstinner commented Jun 11, 2026

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I think we should left commented out calls with an explanatory comment, like for crashes. It indicates that we did not miss these cases, so they will not be reintroduced.

I added this code at the end of the function. Is it what you mean?

        # The following tests are skipped since they rely on undefined behavior
        #self.assertRaises(MemoryError, fromwidechar, b'', PY_SSIZE_T_MAX)
        #self.assertRaises(SystemError, fromwidechar, b'\0'*SIZEOF_WCHAR_T, PY_SSIZE_T_MIN)

serhiy-storchaka
serhiy-storchaka approved these changes Jun 11, 2026
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LGTM. 👍

@vstinner vstinner enabled auto-merge (squash) June 11, 2026 10:36
@vstinner vstinner merged commit d87d772 into python:main Jun 11, 2026
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@vstinner vstinner deleted the test_capi branch June 11, 2026 10:55
@miss-islington-app

miss-islington-app Bot commented Jun 11, 2026

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Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15.
🐍🍒⛏🤖

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bedevere-app Bot commented Jun 11, 2026

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GH-151323 is a backport of this pull request to the 3.15 branch.

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

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GH-151324 is a backport of this pull request to the 3.14 branch.

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

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GH-151325 is a backport of this pull request to the 3.13 branch.

@bedevere-app bedevere-app Bot removed the needs backport to 3.13 bugs and security fixes label Jun 11, 2026
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vstinner commented Jun 11, 2026

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Merged. Thanks for the review @serhiy-storchaka.

vstinner added a commit that referenced this pull request Jun 11, 2026
@miss-islington @vstinner
[3.13] gh-151284: Fix test_capi on UBSan (GH-151286) (#151325)
003db2f 
gh-151284: Fix test_capi on UBSan (GH-151286)

Comment two checks relying on undefined behavior in
test_fromwidechar() of test_capi.

Enable test_capi in GitHub Action "Reusable Sanitizer".
(cherry picked from commit d87d772)

Co-authored-by: Victor Stinner <vstinner@python.org>
vstinner added a commit that referenced this pull request Jun 11, 2026
@miss-islington @vstinner
[3.14] gh-151284: Fix test_capi on UBSan (GH-151286) (#151324)
a258c96 
gh-151284: Fix test_capi on UBSan (GH-151286)

Comment two checks relying on undefined behavior in
test_fromwidechar() of test_capi.

Enable test_capi in GitHub Action "Reusable Sanitizer".
(cherry picked from commit d87d772)

Co-authored-by: Victor Stinner <vstinner@python.org>
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