Re: [PATCH v3 2/4] iio: core: Add opaque_struct_size() helper and use it

[Kees Cook <keescook@chromium.org>]

On Mon, Jul 24, 2023 at 02:11:24PM +0300, Andy Shevchenko wrote:
> On Mon, Jul 24, 2023 at 02:02:02PM +0300, Andy Shevchenko wrote:
> > Introduce opaque_struct_size() helper, which may be moved
> > to overflow.h in the future, and use it in the IIO core.
> > 
> > Potential users could be (among possible others):
> > 
> > 	__spi_alloc_controller() in drivers/spi/spi.c
> > 	alloc_netdev_mqs in net/core/dev.c

Can you include the specific replacement you're thinking for these? It's
almost clear to me, but I'm trying to understand the benefit over what's
already there.

> 
> ...
> 
> > +#define opaque_struct_size(p, a, s)	size_add(ALIGN(sizeof(*(p)), (a)), (s))
> 
> This actually might need something like __safe_aling() which takes care about
> possible overflow.
> 
> Whatever, I want to hear Kees on this.

i.e. if "a" were huge? What would sanity-checking of "a" look like in
this case? I'm not really sure how to handle a pathological alignment
request, but I'd agree it'd be nice to handle it. :)

-Kees

-- 
Kees Cook