Re: BUG #18247: Integer overflow leads to negative width

On Fri, Dec 15, 2023 at 11:30 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Richard Guo <guofenglinux@gmail.com> writes:
> > On Fri, Dec 15, 2023 at 2:00 PM Alexander Lakhin <exclusion@gmail.com>
> >> Your patch looks good to me, but maybe you would find it suitable to
> fix in
> >> passing one more integer overflow in costsize.c?
>
> > Nice catch.  The overflow occurs when cost_bitmap_heap_scan() calls
> > compute_bitmap_pages(), and the loop_count parameter is converted from
> > double to int.  I wonder if we can change the loop_count parameter to be
> > double for compute_bitmap_pages() to avoid such overflow.
>
> However, I'd be a bit uncomfortable about back-patching; since that
> function is globally exposed, it's at least possible that some
> extension is calling it and would see an ABI break.  Is it good enough
> to fix this in HEAD?  I'd argue yes, given that a loop_count larger
> than INT_MAX seems like a pretty improbable case.


I agree with you that it's good enough to fix this in HEAD.  The lack of
complaints from fields for so many years suggests that it's not a common
case to have loop_count larger than INT_MAX.

Thanks
Richard