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Date:   Wed, 25 Aug 2021 22:51:20 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Keith Packard <keithp@keithp.com>
Cc:     linux-kernel@vger.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
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Subject: Re: [PATCH v2 3/5] treewide: Replace 0-element memcpy() destinations
 with flexible arrays
Message-ID: <202108252250.C1DAEE5@keescook>
References: <20210826050458.1540622-1-keescook@chromium.org>
 <20210826050458.1540622-4-keescook@chromium.org>
 <87r1egpym5.fsf@keithp.com>
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On Wed, Aug 25, 2021 at 10:24:18PM -0700, Keith Packard wrote:
> Kees Cook <keescook@chromium.org> writes:
> 
> > In some cases, use of the flex_array() helper is needed when a flexible
> > array is part of a union.
> 
> The code below seems to show that the helper is also needed when the
> flexible array is the only member of a struct? Or is this just an
> extension of the 'part of a union' clause?

That's correct. I have that documented in the DECLARE_FLEX_ARRAY macro
itself, but I mis-spoke in this changelog here (the uses were for "alone
in a struct"). I've adjusted the changelog now. :)

Thanks!

-Kees

> 
> > @@ -160,7 +160,7 @@ struct bmi_cmd {
> >  
> >  union bmi_resp {
> >  	struct {
> > -		u8 payload[0];
> > +		DECLARE_FLEX_ARRAY(u8, payload);
> >  	} read_mem;
> >  	struct {
> >  		__le32 result;
> 
> -- 
> -keith


-- 
Kees Cook