linux-kernel - Re: [PATCH 2/2][next] media: staging/intel-ipu3: css: Replace one-element array and use struct

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Message-ID: <20210730074950.GW1931@kadam>
Date:   Fri, 30 Jul 2021 10:49:50 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Yong Zhi <yong.zhi@...el.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Tianshu Qiu <tian.shu.qiu@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/2][next] media: staging/intel-ipu3: css: Replace
 one-element array and use struct_size() helper

On Thu, Jul 29, 2021 at 06:22:40PM -0500, Gustavo A. R. Silva wrote:
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use “flexible array members”[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
> 
> Replace a one-element array with a flexible-array member in struct
> imgu_fw_header and use the struct_size() helper.
> 
> This also helps with the ongoing efforts to globally enable
> -Warray-bounds and get us closer to being able to tighten the
> FORTIFY_SOURCE routines on memcpy().
> 
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Link: https://github.com/KSPP/linux/issues/79
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/staging/media/ipu3/ipu3-css-fw.c | 5 ++---
>  drivers/staging/media/ipu3/ipu3-css-fw.h | 2 +-
>  2 files changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/media/ipu3/ipu3-css-fw.c b/drivers/staging/media/ipu3/ipu3-css-fw.c
> index ab021afff954..3b7df1128840 100644
> --- a/drivers/staging/media/ipu3/ipu3-css-fw.c
> +++ b/drivers/staging/media/ipu3/ipu3-css-fw.c
> @@ -127,9 +127,8 @@ int imgu_css_fw_init(struct imgu_css *css)
>  	if (css->fw->size < sizeof(struct imgu_fw_header) ||
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Originally this was sizeof() the pointer which is clearly wrong.  Then
patch 1 changed it to force that binary_header[] had at least one
element, but now it's changed again to say that binary_header[] can have
zero elements.  So either patch 1 or patch 2 is wrong.

I feel like the probably the correct fix is to just fold these two
patches together and say that binary_header[] with zero elements is
allowed.  But I don't know this code well.

regards,
dan carpenter