linux-hardening - Re: [PATCH v2][next] cgroup: Avoid -Wstringop-overflow warnings

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Message-ID: <202308161356.4AED47263E@keescook>
Date:   Wed, 16 Aug 2023 13:57:16 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2][next] cgroup: Avoid -Wstringop-overflow warnings

On Wed, Aug 16, 2023 at 10:51:12AM -1000, Tejun Heo wrote:
> Hello,
> 
> On Wed, Aug 16, 2023 at 02:50:16PM -0600, Gustavo A. R. Silva wrote:
> > Change the notation from pointer-to-array to pointer-to-pointer.
> > With this, we avoid the compiler complaining about trying
> > to access a region of size zero as an argument during function
> > calls.
> 
> Haha, I thought the functions were actually accessing the memory. This can't
> be an intended behavior on the compiler's side, right?

I think it's a result of inlining -- the compiler ends up with a case
where it looks like it might be possible to index a zero-sized array,
but it is "accidentally safe".

-- 
Kees Cook