linux-hardening - Re: [PATCH 1/2] stddef: Allow attributes to be used when creating flex arrays

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Date: Tue, 13 Feb 2024 15:20:58 -0800
From: Kees Cook <keescook@...omium.org>
To: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Jakub Kicinski <kuba@...nel.org>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Keith Packard <keithp@...thp.com>, Miguel Ojeda <ojeda@...nel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Dmitry Antipov <dmantipov@...dex.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Nathan Chancellor <nathan@...nel.org>,
	kernel test robot <lkp@...el.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 1/2] stddef: Allow attributes to be used when creating
 flex arrays

On Tue, Feb 13, 2024 at 08:22:00AM +0100, Rasmus Villemoes wrote:
> On 10/02/2024 02.16, Kees Cook wrote:
> > With the coming support for the __counted_by struct member attribute, we
> > will need a way to add such annotations to the places where
> > DECLARE_FLEX_ARRAY() is used. Introduce DECLARE_FLEX_ARRAY_ATTR() which
> > takes a third argument: the attributes to apply to the flexible array.
> > 
> 
> > - * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
> > - *
> > + * __DECLARE_FLEX_ARRAY_ATTR() - Declare a flexible array usable in a union
> >   * @TYPE: The type of each flexible array element
> >   * @NAME: The name of the flexible array member
> > + * @ATTRS: The list of member attributes to apply
> >   *
> >   * In order to have a flexible array member in a union or alone in a
> >   * struct, it needs to be wrapped in an anonymous struct with at least 1
> >   * named member, but that member can be empty.
> >   */
> > -#define __DECLARE_FLEX_ARRAY(TYPE, NAME)	\
> > +#define __DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS)	\
> >  	struct { \
> >  		struct { } __empty_ ## NAME; \
> > -		TYPE NAME[]; \
> > +		TYPE NAME[] ATTRS; \
> >  	}
> 
> Is it too ugly to not introduce a separate _ATTR macro but instead just do
> 
> #define __DECLARE_FLEX_ARRAY(TYPE, NAME, ...) \
>   ...
>   TYPE NAME[] __VA_ARGS__;
> 
> ?

Oh, yes. That will be much nicer, I think! I will send a v2...

-- 
Kees Cook