linux-hardening - Re: [PATCH] fbdev: Replace 0-length array with flexible array

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Date:   Fri, 6 Jan 2023 09:54:11 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Helge Deller <deller@....de>, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] fbdev: Replace 0-length array with flexible array

On Thu, Jan 05, 2023 at 11:20:38AM -0800, Kees Cook wrote:
> Zero-length arrays are deprecated[1]. Replace struct aperture's "ranges"
> 0-length array with a flexible array. (How is the size of this array
> verified?) Detected with GCC 13, using -fstrict-flex-arrays=3:
> 
> samples/vfio-mdev/mdpy-fb.c: In function 'mdpy_fb_probe':
> samples/vfio-mdev/mdpy-fb.c:169:32: warning: array subscript 0 is outside array bounds of 'struct aperture[0]' [-Warray-bounds=]
>   169 |         info->apertures->ranges[0].base = info->fix.smem_start;
>       |         ~~~~~~~~~~~~~~~~~~~~~~~^~~
> In file included from samples/vfio-mdev/mdpy-fb.c:21:
> include/linux/fb.h:510:19: note: while referencing 'ranges'
>   510 |                 } ranges[0];
>       |                   ^~~~~~
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Cc: Helge Deller <deller@....de>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: linux-fbdev@...r.kernel.org
> Cc: dri-devel@...ts.freedesktop.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks!
--
Gustavo

> ---
>  include/linux/fb.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/fb.h b/include/linux/fb.h
> index 96b96323e9cb..bf59d6a3590f 100644
> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -507,7 +507,7 @@ struct fb_info {
>  		struct aperture {
>  			resource_size_t base;
>  			resource_size_t size;
> -		} ranges[0];
> +		} ranges[];
>  	} *apertures;
>  
>  	bool skip_vt_switch; /* no VT switch on suspend/resume required */
> -- 
> 2.34.1
>