gh-150599: Prevent bz2 decompressor reuse after errors

[StanFromIreland]

• Issue: Stack buffer overflow in bz2 when reusing BZ2Decompressor after error #150599

[serhiy-storchaka]

Why reraise the same error again and again? Why not close the decomressor, set eof and raise EOFError? Or set other flag and raise ValueError or RuntimeError?

[StanFromIreland]

Serhiy, FYI this is the fix for: https://github.com/python/cpython/security/advisories/GHSA-mv83-7xc2-cc7v

Why reraise the same error again and again? Why not close the decomressor, set eof and raise EOFError? Or set other flag and raise ValueError or RuntimeError?

Setting eof and raising EOFError would lie about the state as the stream did not finish cleanly. ValueError/RuntimeError would make the second call report a different kind of failure from the first call, even though the root cause is the same. I think re-raising the same exception is the most useful behaviour, it preserves the original failure reason.

[serhiy-storchaka]

You are not supposed to use decompressor after failure. Raising a ValueError or a RuntimeError with specific error message ("decompressor is dead, don't use it") will make it clear.

[StanFromIreland]

You are not supposed to use decompressor after failure. Raising a ValueError or a RuntimeError with specific error message ("decompressor is dead, don't use it") will make it clear.

It is clear, I'm still leaning towards providing the root cause being more helpful. Greg and Emma, what do you think is better here?

[serhiy-storchaka]

You already got the initial error first time. There is no precedence of keeping the original error and raising it on recurring requests.

[StanFromIreland]

Ok, we also raise a ValueError after flush(), so I changed it.

cpython/Modules/_bz2module.c

Lines 267 to 268 in 494f2e3

	if (self->flushed)
	PyErr_SetString(PyExc_ValueError, "Compressor has been flushed");

[serhiy-storchaka]

LGTM. 👍

[miss-islington-app]

Thanks @StanFromIreland for the PR, and @emmatyping for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10, 3.11, 3.12, 3.13, 3.14, 3.15.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @StanFromIreland and @emmatyping, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 5755d0f083949ff3c5bf3a37e673e24e306b036e 3.14

[miss-islington-app]

Sorry, @StanFromIreland and @emmatyping, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 5755d0f083949ff3c5bf3a37e673e24e306b036e 3.13

[bedevere-app]

GH-151045 is a backport of this pull request to the 3.15 branch.

[miss-islington-app]

Sorry, @StanFromIreland and @emmatyping, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 5755d0f083949ff3c5bf3a37e673e24e306b036e 3.12

[miss-islington-app]

Sorry, @StanFromIreland and @emmatyping, I could not cleanly backport this to 3.11 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 5755d0f083949ff3c5bf3a37e673e24e306b036e 3.11

[miss-islington-app]

Sorry, @StanFromIreland and @emmatyping, I could not cleanly backport this to 3.10 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 5755d0f083949ff3c5bf3a37e673e24e306b036e 3.10

[bedevere-app]

GH-151054 is a backport of this pull request to the 3.14 branch.

[StanFromIreland]

The others should hopefully come cleanly from #151054.

[bedevere-app]

GH-151055 is a backport of this pull request to the 3.13 branch.

[bedevere-app]

GH-151057 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-151132 is a backport of this pull request to the 3.11 branch.

[bedevere-app]

GH-151133 is a backport of this pull request to the 3.10 branch.