Re: BUG #16176: NULL value returned by category_sql argument to crosstab() causes segmentation fault

On 12/20/19 1:00 PM, Tom Lane wrote:
> PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
>> -- this will crash pg12, but not version() < 12 - note NULL value in
>> categories query:
>> select * from crosstab ('values (1, 2, 12), (1, 3, 13), (2, 2, 22), (2,
>> 3, 23), (3, 2, 32), (3, 3, 33) order by 1, 2, 3', 'values (2), (null)') as
>> rr (a int, "2" int, "3" int);
>
> Yeah, duplicated here. It seems tablefunc is passing a NULL string
> pointer to sprintf(). Previously, that would work on some platforms
> and crash on others --- as of v12, it crashes everywhere.
>
> What we need here is to figure out what the hashtab string key ought
> to be for a NULL category. I suspect what was happening before
> (on non-crashing platforms) was that you implicitly got "(nil)"
> or some spelling like that, which is not great because it could
> conflict with a valid user key. Alternatively, we could refuse
> NULL category values ... not sure if that's desirable.
>
> Anyway, this is *not* a new bug, it's just possible to hit it on
> more platforms now.

Thanks for the heads up -- I'll take a look as quick as I can, but
likely tomorrow.

Joe

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