linux-kernel - Re: [PATCH] soc: fsl: qe: Replace one-element array and use struct

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Message-ID: <CADRPPNST6qhAHAEKXAnnJhQhoyb=r5O5YVs2KJW5qNgOjanu-Q@mail.gmail.com>
Date:   Fri, 22 May 2020 16:23:46 -0500
From:   Li Yang <leoyang.li@....com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Qiang Zhao <qiang.zhao@....com>, Kees Cook <keescook@...omium.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: Re: [PATCH] soc: fsl: qe: Replace one-element array and use
 struct_size() helper

On Mon, May 18, 2020 at 5:16 PM Gustavo A. R. Silva
<gustavoars@...nel.org> wrote:
>
> The current codebase makes use of one-element arrays in the following
> form:
>
> struct something {
>     int length;
>     u8 data[1];
> };
>
> struct something *instance;
>
> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> instance->length = size;
> memcpy(instance->data, source, size);
>
> 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
> inadvertently introduced[3] to the codebase from now on. So, replace
> the one-element array with a flexible-array member.
>
> Also, make use of the new struct_size() helper to properly calculate the
> size of struct qe_firmware.
>
> This issue was found with the help of Coccinelle and, audited and fixed
> _manually_.
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/soc/fsl/qe/qe.c | 4 ++--
>  include/soc/fsl/qe/qe.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)

Applied for next.  Thanks.

Regards,
Leo