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devdanzin opened this issue Apr 13, 2025 · 2 comments
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Building a ctypes.CField with wrong byte_size aborts #132470

devdanzin opened this issue Apr 13, 2025 · 2 comments
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3.14 bugs and security fixes extension-modules C modules in the Modules dir topic-ctypes type-crash A hard crash of the interpreter, possibly with a core dump

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@devdanzin
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devdanzin commented Apr 13, 2025 •
edited by bedevere-app bot
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Crash report

What happened?

The following code will cause an abort due to byte_size not matching the size of ctypes.c_byte, failing an assertion that byte_size == info->size.

import ctypes
ctypes.CField(name="a", type=ctypes.c_byte, byte_size=2, byte_offset=2, index=1, _internal_use=True)

Abort message:

python: ./Modules/_ctypes/cfield.c:102: PyCField_new_impl: Assertion `byte_size == info->size' failed.

Aborted (core dumped)

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.14.0a6+ (heads/main:be2d2181e62, Mar 31 2025, 07:30:17) [GCC 11.4.0]

Linked PRs
@devdanzin devdanzin added the type-crash A hard crash of the interpreter, possibly with a core dump label Apr 13, 2025
@picnixz picnixz added topic-ctypes extension-modules C modules in the Modules dir 3.14 bugs and security fixes and removed topic-ctypes extension-modules C modules in the Modules dir type-crash A hard crash of the interpreter, possibly with a core dump labels Apr 13, 2025
@picnixz
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picnixz commented Apr 13, 2025

Field wasn't meant to be used publicly for now but, since it's a real crash and if we're to expose this interface in the future, we would be happy to have this check.

@picnixz picnixz added topic-ctypes extension-modules C modules in the Modules dir type-crash A hard crash of the interpreter, possibly with a core dump labels Apr 13, 2025
dura0ok added a commit to dura0ok/cpython that referenced this issue Apr 13, 2025
@dura0ok
Fix: Prevent crash in ctypes.CField when byte_size does not match typ…
45aa6a3 
…e size (pythongh-132470)

When creating a ctypes.CField with an incorrect byte_size (e.g., using byte_size=2 for ctypes.c_byte), the code would previously abort due to the failed assertion byte_size == info->size.

This commit replaces the assertion with a proper error handling mechanism that raises a ValueError when byte_size does not match the expected type size. This prevents the crash and provides a more informative error message to the us
@bedevere-app bedevere-app bot mentioned this issue Apr 13, 2025
Merged
dura0ok added a commit to dura0ok/cpython that referenced this issue Apr 13, 2025
@dura0ok
Add regression test for invalid byte_size in ctypes.CField
c869028 
Adds a test to ensure that creating a ctypes.CField with a byte_size
that doesn't match the underlying C type size (e.g., 2 bytes for c_byte)
correctly raises a ValueError. This test verifies the fix for pythongh-132470
and prevents future regressions where such mismatches could cause an abort.
dura0ok added a commit to dura0ok/cpython that referenced this issue Apr 13, 2025
@dura0ok
Add regression test for invalid byte_size in ctypes.CField
c52e20f 
Adds a test to ensure that creating a ctypes.CField with a byte_size
that doesn't match the underlying C type size (e.g., 2 bytes for c_byte)
correctly raises a ValueError. This test verifies the fix for pythongh-132470
and prevents future regressions where such mismatches could cause an abort.
dura0ok added a commit to dura0ok/cpython that referenced this issue Apr 13, 2025
@dura0ok
Add regression test for invalid byte_size in ctypes.CField
3377d9a 
Adds a test to ensure that creating a ctypes.CField with a byte_size
that doesn't match the underlying C type size (e.g., 2 bytes for c_byte)
correctly raises a ValueError. This test verifies the fix for pythongh-132470
and prevents future regressions where such mismatches could cause an abort.
sobolevn added a commit that referenced this issue Apr 22, 2025
@dura0ok @sobolevn
gh-132470: Prevent crash in ctypes.CField when byte_size is incorre…
3b4b56f 
…ct (#132475)

Fix: Prevent crash in ctypes.CField when byte_size does not match type size  (gh-132470)

When creating a ctypes.CField with an incorrect byte_size (e.g., using `byte_size=2` for `ctypes.c_byte`), the code would previously abort due to the failed assertion `byte_size == info->size`.

This commit replaces the assertion with a proper error handling mechanism that raises a `ValueError` when `byte_size` does not match the expected type size. This prevents the crash and provides a more informative error message to the us

Co-authored-by: sobolevn <[email protected]>
@encukou
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encukou commented Apr 28, 2025

To set expectations: the CField initializer is indeed not public. If you use _internal_use=True, you are on your own -- don't blame CPython if it crashes.

With that said, thank you for testing this internal API! And thank you for the fix -- when CField becomes public, there'll be one less thing to do.

@encukou encukou closed this as completed Apr 28, 2025
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