linux-hardening - Re: [PATCH] docs: deprecated.rst: Add note about DECLARE_FLEX

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Date:   Thu, 12 Jan 2023 11:38:25 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Jonathan Corbet <corbet@....net>
Cc:     Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] docs: deprecated.rst: Add note about
 DECLARE_FLEX_ARRAY() usage

On Wed, Jan 11, 2023 at 04:11:41PM -0700, Jonathan Corbet wrote:
> Kees Cook <keescook@...omium.org> writes:
> 
> > There wasn't any mention of when/where DECLARE_FLEX_ARRAY() should be
> > used, so add the rationale and an example to the deprecation docs.
> >
> > Suggested-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>
> > Cc: Jonathan Corbet <corbet@....net>
> > Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> > Cc: linux-doc@...r.kernel.org
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  Documentation/process/deprecated.rst | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> 
> I've applied this, but couldn't resist making one tweak...
> 
> > diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
> > index c8fd53a11a20..fcac0a929efa 100644
> > --- a/Documentation/process/deprecated.rst
> > +++ b/Documentation/process/deprecated.rst
> > @@ -346,3 +346,29 @@ struct_size() and flex_array_size() helpers::
> >          instance->count = count;
> >  
> >          memcpy(instance->items, source, flex_array_size(instance, items, instance->count));
> > +
> > +There are two special cases of replacement where the DECLARE_FLEX_ARRAY()
> > +helper needs to be used. (Note that it is named __DECLARE_FLEX_ARRAY() for
> > +use in UAPI headers.) When the flexible array is either alone in a struct,
> > +or is part of a union. 
> 
> The pedant in me couldn't stand leaving that sentence fragment, so I
> made a complete sentence out of it.

Thank you; I appreciate the help! :)

-- 
Kees Cook