linux-kernel - Re: [PATCH] staging: Replace zero-length array with flexible-array member

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d331cd9c-ec57-b686-d977-c48e70415ae1@microchip.com>
Date:   Thu, 20 Feb 2020 19:04:48 +0000
From:   <Adham.Abozaeid@...rochip.com>
To:     <gustavo@...eddedor.com>, <gregkh@...uxfoundation.org>,
        <vaibhav.sr@...il.com>, <mgreer@...malcreek.com>,
        <johan@...nel.org>, <elder@...nel.org>, <m.tretter@...gutronix.de>,
        <kernel@...gutronix.de>, <mchehab@...nel.org>,
        <Larry.Finger@...inger.net>, <florian.c.schilhabel@...glemail.com>,
        <Ajay.Kathat@...rochip.com>
CC:     <devel@...verdev.osuosl.org>, <linux-kernel@...r.kernel.org>,
        <greybus-dev@...ts.linaro.org>, <linux-media@...r.kernel.org>,
        <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH] staging: Replace zero-length array with flexible-array
 member

Hi Gustavo

On 2/20/20 6:29 AM, 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
> inadvertently introduced[3] to the codebase from now on.
>
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
>
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
>
> This issue was found with the help of Coccinelle.
>
> [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 <gustavo@...eddedor.com>
>
>  static void cfg_scan_result(enum scan_event scan_event,
> diff --git a/drivers/staging/wilc1000/spi.c b/drivers/staging/wilc1000/spi.c
> index 44f7d48851b5..11653ac118cd 100644
> --- a/drivers/staging/wilc1000/spi.c
> +++ b/drivers/staging/wilc1000/spi.c
> @@ -139,7 +139,7 @@ struct wilc_spi_read_rsp_data {
>         u8 status;
>         u8 resp_header;
>         u8 resp_data[4];
> -       u8 crc[0];
> +       u8 crc[];
>  } __packed;
more zero-length arrays in wilc1000, spi.c, struct wilc_spi_cmd, and in fw.h