overflow checking for modification time (64-bit, import.c)

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

BPO	400509
Nosy	@tim-one, @freddrake
Files	None: None

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields: ```python assignee = 'https://github.com/freddrake' closed_at = created_at = labels = [] title = 'overflow checking for modification time (64-bit, import.c)' updated_at = user = 'https://bugs.python.org/tmick' ``` bugs.python.org fields: ```python activity = actor = 'fdrake' assignee = 'fdrake' closed = True closed_date = None closer = None components = ['None'] creation = creator = 'tmick' dependencies = [] files = ['2440'] hgrepos = [] issue_num = 400509 keywords = ['patch'] message_count = 5.0 messages = ['32703', '32704', '32705', '32706', '32707'] nosy_count = 3.0 nosy_names = ['tim.peters', 'fdrake', 'tmick'] pr_nums = [] priority = 'normal' resolution = None stage = None status = 'closed' superseder = None type = None url = 'https://bugs.python.org/issue400509' versions = [] ```

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

[freddrake]

Checked in verbatim.

[tim-one]

Hey! I can review these in my sleep now \<wink>! Accepted & passed back to Trent.

[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

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[bdaf8532-ded6-4d4c-9bb3-51fd76040dc1]

This patch fixes possible overflow in the use of PyOS_GetLastModificationTime in getmtime.c and Python/import.c.

Currently PyOS_GetLastModificationTime returns a C long. This can overflow on Win64 where sizeof(time_t) > sizeof(long). Besides it should logically return a time_t anyway (this patch changes this).

As well, import.c uses PyOS_GetLastModificationTime for .pyc timestamping. There has been recent discussion about the .pyc header format on python-dev. This patch adds oveflow checking to import.c so that an exception will be raised if the modification time overflows. There are a few other minor 64-bit readiness changes made to the module as well:

• size_t instead of int or long for function-local buffer and string length variables
• one buffer overflow check was added (raises an exception on possible overflow, this overflow chance exists on 32-bit platforms as well), no other possible buffer overflows existed (from my analysis anyway)