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On Python 3, but not Python 2, you crash with a Segmentation Fault instead of getting a MemoryError as expected. It seems to only be a problem with bytearray, not with other things like tuple:
$ python3
Python 3.4.0 (default, Apr 11 2014, 13:05:18) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> bytearray(0x7FFFFFFF)
Segmentation fault (core dumped)
$ 
compare to:
$ python
Python 2.7.6 (default, Mar 22 2014, 22:59:38) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> bytearray(0x7FFFFFFF)
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
MemoryError
>>> 
$ python3
Python 3.4.0 (default, Apr 11 2014, 13:05:18) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> (0,)*0x7FFFFFFF
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
MemoryError
>>>

Looks as integer overflow introduced in issue19087.
+ if (size + logical_offset + 1 < alloc) {

This patch should fix it.

On a second thought, "logical_offset + 1" alone could overflow; and there are apparently other possible integer overflows in this function.

"logical_offset + 1" can't overflow because logical_offset is an offset in allocated array not counting final null byte.

Note that there are two possible crashes in debug mode:
$ ./python -c "bytearray(2**31-1)"
Erreur de segmentation
$ ./python -c "bytearray(2**31-2)"
python: Objects/obmalloc.c:1179: _PyObject_Alloc: Assertion `nelem <= ((Py_ssize_t)(((size_t)-1)>>1)) / elsize' failed.
Abandon

Here is a patch. It also fixes a bug in the debug allocators, which didn't properly check for Py_ssize_t overflow.

LGTM.

New changeset 1590c594550e by Antoine Pitrou in branch '3.4':
Issue #22335: Fix crash when trying to enlarge a bytearray to 0x7fffffff bytes on a 32-bit platform.
https://hg.python.org/cpython/rev/1590c594550e
New changeset f0b334ae95c9 by Antoine Pitrou in branch 'default':
Issue #22335: Fix crash when trying to enlarge a bytearray to 0x7fffffff bytes on a 32-bit platform.
https://hg.python.org/cpython/rev/f0b334ae95c9 

Thank you. This is now pushed.