Subject: Re: [PATCH] evaluate the second argument of ALLOC_GROW only once

From: Jeff King <[email-masked]>
Date: Fri, 15 May 2026 15:08:18 -0400

On Fri, May 15, 2026 at 08:16:50PM +0200, René Scharfe wrote:

> +		size_t alloc_grow_new_alloc_; \
> +		if (st_alloc_nr((nr), (alloc), &alloc_grow_new_alloc_)) { \
> +			alloc = alloc_grow_new_alloc_; \
> +			REALLOC_ARRAY(x, alloc_grow_new_alloc_); \
>  		} \

What happens if a caller passes in an argument that isn't a size_t?
We'll check for overflow in the size_t space, and then truncate it when
we assign to alloc, I think.

I think we generally try to hold allocations in size_t these days, but
I'd be surprised if there weren't a few "int" holdouts. Grepping around,
alloc_node() seems to be an example.

BTW, non-size_t arguments nullifies my earlier hand-waving around "nr +
1 overflowing implies we've filled up the address space". But we are
still protected in the existing code by the:

  if (alloc_nr(alloc) < (nr))
	alloc = (nr);

logic. But with your patch, that all happens in the size_t space, so I
think it would actually introduce possible array overflows when the
caller is using a smaller type.

-Peff