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gh-126238: Fix possible null pointer dereference of freevars in _PyCompile_LookupArg #126239

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Merged
merged 4 commits into from
Nov 5, 2024
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gh-126238: Fix possible null pointer dereference of freevars in _PyCompile_LookupArg #126239

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f8940e4
Replace Py_DECREF by Py_XDECREF
federicovalenso Oct 31, 2024
10dcbe0
📜🤖 Added by blurb_it.
blurb-it[bot] Oct 31, 2024
2c8bc0f
Update Misc/NEWS.d/next/Security/2024-10-31-13-14-27.gh-issue-126238.…
federicovalenso Oct 31, 2024
547eca1
Remove news entry due to "skip news" label
federicovalenso Nov 1, 2024
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Security/2024-10-31-13-14-27.gh-issue-126238.CZqaon.rst
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@@ -0,0 +1 @@
Fix a possible crash internally when compiling.
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I suggest to drop this NEWS entry.

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I concur (that's what I did for #126241 because it's a bit hard to phrase it properly and meaningfully).

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drop this NEWS entry

Done )

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Why? This seems user-facing to me, isn't it?

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@sobolevn, @picnixz , what's the bottom line? Is news entry required or not?

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@picnixz picnixz Nov 1, 2024 •
edited
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The bottom line in general is whether this kind of bug can be triggered easily using public interface. Unless you have a reproducer saying that with X and Y you can do Z, or unless the interface is publicly documented and known to the outside world, a NEWS entry would be fine. But here, we have neither a test nor is _PyCompile_LookupArg something that is exposed to the world.

As an end-user, reading "Fix a possible crash internally when compiling." gives me no information at all except that there was a bug I wasn't aware of (and that it was not always triggerable). I don't know how to make the crash happen, nor do I know what was crashing.

2 changes: 1 addition & 1 deletion Python/compile.c
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Expand Up @@ -901,7 +901,7 @@ _PyCompile_LookupArg(compiler *c, PyCodeObject *co, PyObject *name)
c->u->u_metadata.u_name,
co->co_name,
freevars);
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Does PyErr_Format work for null?

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Yes, %R formats it as "<NULL>"

Py_DECREF(freevars);
Py_XDECREF(freevars);
return ERROR;
}
return arg;
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