netdev - Re: [PATCH] treewide: Replace zero-length arrays with flexible-array member

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Message-ID: <202002111132.4A4F073CAF@keescook>
Date:   Tue, 11 Feb 2020 11:35:50 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] treewide: Replace zero-length arrays with flexible-array
 member

On Tue, Feb 11, 2020 at 11:41:26AM -0600, Gustavo A. R. Silva wrote:
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
> 
> struct foo {
>         int stuff;
>         struct boo array[];
> };
> 
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> unadvertenly introduced[3] to the codebase from now on.

Is there a compiler warning we can enable to avoid new 0-byte arrays
from entering the kernel source tree? I can only find "-pedantic" which
enables way too many other checks.

-- 
Kees Cook