gh-145376: Fix refleak and null pointer deref in unusual error path of datetime module

[eendebakpt]

• Issue: Various reference leaks in the core #145376

[StanFromIreland]

I think this should get a news entry.

[eendebakpt]

I think this should get a news entry.

Added the news entry, although I think we can skip it since the changes are only in very rare paths.

[encukou]

I think we can skip [a news entry] since the changes are only in very rare paths.

That's my assesment too. It's technically a user-visible change, but that user needs to squint really hard.

[vstinner]

Please remove it, users should not be impacted by this change. The error case is very unlikely.

[StanFromIreland]

I suggested adding it since this PR covers several cases increasing the likelyhood of one of them being hit. If you think it is better to remove it, I don't mind.

[vstinner]

Usually, we don't document such fix for an unlikely corner case.

PyLong_FromLong() can only fail if the system has no more free memory.

datetime.datetime.astimezone() reads freed memory, but it only occurs if utcoffset() returns the wrong type. It seems like nobody reported the issue (with a reproducer), so it sounds unlikely to crash in practice (reading freed memory just works in the common case).

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.x (tier-2) has failed when building commit 0eaf260.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/725/builds/12928) and take a look at the build logs.
4. Check if the failure is related to this commit (0eaf260) or if it is a false positive.
5. 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/725/builds/12928

Failed tests:

• test_urllib2net

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

==

Click to see traceback logs

remote: Enumerating objects: 4, done.        
remote: Counting objects:  25% (1/4)        
remote: Counting objects:  50% (2/4)        
remote: Counting objects:  75% (3/4)        
remote: Counting objects: 100% (4/4)        
remote: Counting objects: 100% (4/4), done.        
remote: Compressing objects:  25% (1/4)        
remote: Compressing objects:  50% (2/4)        
remote: Compressing objects:  75% (3/4)        
remote: Compressing objects: 100% (4/4)        
remote: Compressing objects: 100% (4/4), done.        
remote: Total 4 (delta 0), reused 1 (delta 0), pack-reused 0 (from 0)        
From https://github.com/python/cpython
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HEAD is now at 0eaf260d79f gh-145376: Fix refleak and null pointer deref in unusual error path of datetime module (GH-145476)
Switched to and reset branch 'main'

make: *** [buildbottest] Error 2