gh-120384: Fix array-out-of-bounds crash in list_ass_subscript

[sobolevn]

Thank a lot to @MechanicPig for the reproducer and detailed bug description.

• Issue: Array out of bounds assignment in list_ass_subscript #120384

[sobolevn]

and there's a leak now, fixing.

[serhiy-storchaka]

LGTM.

[sobolevn]

Thank you, very helpful review 👍

[miss-islington-app]

Thanks @sobolevn for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[miss-islington-app]

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

[bedevere-app]

GH-120825 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-120826 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot iOS ARM64 Simulator 3.x has failed when building commit 8334a1b.

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/all/#builders/1380/builds/655) and take a look at the build logs.
4. Check if the failure is related to this commit (8334a1b) 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/all/#builders/1380/builds/655

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

Click to see traceback logs

remote: Enumerating objects: 13, done.        
remote: Counting objects:   8% (1/12)        
remote: Counting objects:  16% (2/12)        
remote: Counting objects:  25% (3/12)        
remote: Counting objects:  33% (4/12)        
remote: Counting objects:  41% (5/12)        
remote: Counting objects:  50% (6/12)        
remote: Counting objects:  58% (7/12)        
remote: Counting objects:  66% (8/12)        
remote: Counting objects:  75% (9/12)        
remote: Counting objects:  83% (10/12)        
remote: Counting objects:  91% (11/12)        
remote: Counting objects: 100% (12/12)        
remote: Counting objects: 100% (12/12), done.        
remote: Compressing objects:   8% (1/12)        
remote: Compressing objects:  16% (2/12)        
remote: Compressing objects:  25% (3/12)        
remote: Compressing objects:  33% (4/12)        
remote: Compressing objects:  41% (5/12)        
remote: Compressing objects:  50% (6/12)        
remote: Compressing objects:  58% (7/12)        
remote: Compressing objects:  66% (8/12)        
remote: Compressing objects:  75% (9/12)        
remote: Compressing objects:  83% (10/12)        
remote: Compressing objects:  91% (11/12)        
remote: Compressing objects: 100% (12/12)        
remote: Compressing objects: 100% (12/12), done.        
remote: Total 13 (delta 0), reused 0 (delta 0), pack-reused 1        
From https://github.com/python/cpython
 * branch                  main       -> FETCH_HEAD
Note: switching to '8334a1b55c93068f5d243852029baa83377ff6c9'.

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Or undo this operation with:

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Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 8334a1b55c gh-120384: Fix array-out-of-bounds crash in `list_ass_subscript` (#120442)
Switched to and reset branch 'main'

configure: WARNING: no system libmpdecimal found; falling back to bundled libmpdecimal (deprecated and scheduled for removal in Python 3.15)
configure: WARNING: pkg-config is missing. Some dependencies may not be detected correctly.

configure: WARNING: no system libmpdecimal found; falling back to bundled libmpdecimal (deprecated and scheduled for removal in Python 3.15)
configure: WARNING: pkg-config is missing. Some dependencies may not be detected correctly.

../../Modules/_sqlite/connection.c:1307:14: warning: 'sqlite3_create_window_function' is only available on iOS 13.0 or newer [-Wunguarded-availability-new]
        rc = sqlite3_create_window_function(self->db, name, num_params, flags,
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator17.5.sdk/usr/include/sqlite3.h:5533:16: note: 'sqlite3_create_window_function' has been marked as being introduced in iOS 13.0 here, but the deployment target is iOS 12.0.0
SQLITE_API int sqlite3_create_window_function(
               ^
../../Modules/_sqlite/connection.c:1307:14: note: enclose 'sqlite3_create_window_function' in a __builtin_available check to silence this warning
        rc = sqlite3_create_window_function(self->db, name, num_params, flags,
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../Modules/_sqlite/connection.c:1315:14: warning: 'sqlite3_create_window_function' is only available on iOS 13.0 or newer [-Wunguarded-availability-new]
        rc = sqlite3_create_window_function(self->db, name, num_params, flags,
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator17.5.sdk/usr/include/sqlite3.h:5533:16: note: 'sqlite3_create_window_function' has been marked as being introduced in iOS 13.0 here, but the deployment target is iOS 12.0.0
SQLITE_API int sqlite3_create_window_function(
               ^
../../Modules/_sqlite/connection.c:1315:14: note: enclose 'sqlite3_create_window_function' in a __builtin_available check to silence this warning
        rc = sqlite3_create_window_function(self->db, name, num_params, flags,
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 warnings generated.

--- xcodebuild: WARNING: Using the first of multiple matching destinations:
{ platform:iOS Simulator, id:C6AEA11C-C34A-47B8-BD67-AF0403ECA353, OS:17.5, name:iPhone SE (3rd generation) }
{ platform:iOS Simulator, id:C6AEA11C-C34A-47B8-BD67-AF0403ECA353, OS:17.5, name:iPhone SE (3rd generation) }
2024-06-21 11:16:45.090 xcodebuild[33218:87319398] [MT] IDETestOperationsObserverDebug: 1075.762 elapsed -- Testing started completed.
2024-06-21 11:16:45.090 xcodebuild[33218:87319398] [MT] IDETestOperationsObserverDebug: 0.000 sec, +0.000 sec -- start
2024-06-21 11:16:45.090 xcodebuild[33218:87319398] [MT] IDETestOperationsObserverDebug: 1075.762 sec, +1075.762 sec -- end
Failing tests:
	-[iOSTestbedTests testPython]

** TEST FAILED **

make: *** [testios] Error 1