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

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Message-ID: <32c7ea41-8b00-c92e-02ec-d535428e55bb@embeddedor.com>
Date:   Thu, 17 Aug 2023 11:23:38 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Tejun Heo <tj@...nel.org>, Kees Cook <keescook@...omium.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 8/16/23 15:01, Tejun Heo wrote:
> On Wed, Aug 16, 2023 at 01:57:16PM -0700, Kees Cook wrote:
>> 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".
> 
> Ah I see. It's not that the compiler knows that ** access is safe. It's more
> that it only applies the check on arrays. Is that right? Gustavo, I don't

That's correct.

> mind the patch but can you update the patch description a bit explaining a
> bit more on what's going on with the complier? It doesn't have to be the
> full explanation but it'd be useful to explicitly point out that we're just
> working around the compiler being a bit silly.

I just sent v3:

	https://lore.kernel.org/linux-hardening/ZN5WkbPelHUSTXOA@work/

Thanks
--
Gustavo