linux-kernel - Re: [PATCH] drm/fbdev-generic: fix potential out-of-bounds access

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Message-ID: <1bbc7228-c2fe-0af0-c15c-b378bc4d111c@suse.de>
Date:   Thu, 13 Apr 2023 21:20:23 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Sui Jingfeng <15330273260@....cn>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...il.com>, Li Yi <liyi@...ngson.cn>,
        Helge Deller <deller@....de>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] drm/fbdev-generic: fix potential out-of-bounds access

Hi

Am 13.04.23 um 20:56 schrieb Daniel Vetter:
[...]
> 
> This should switch the existing code over to using drm_framebuffer instead
> of fbdev:
> 
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index ef4eb8b12766..99ca69dd432f 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -647,22 +647,26 @@ static void drm_fb_helper_damage(struct drm_fb_helper *helper, u32 x, u32 y,
>   static void drm_fb_helper_memory_range_to_clip(struct fb_info *info, off_t off, size_t len,
>   					       struct drm_rect *clip)
>   {
> +	struct drm_fb_helper *helper = info->par;
> +
>   	off_t end = off + len;
>   	u32 x1 = 0;
>   	u32 y1 = off / info->fix.line_length;
> -	u32 x2 = info->var.xres;
> -	u32 y2 = DIV_ROUND_UP(end, info->fix.line_length);
> +	u32 x2 = helper->fb->height;
> +	unsigned stride = helper->fb->pitches[0];
> +	u32 y2 = DIV_ROUND_UP(end, stride);
> +	int bpp = drm_format_info_bpp(helper->fb->format, 0);

Please DONT do that. The code here is fbdev code and shouldn't bother 
about DRM data structures. Actually, it shouldn't be here: a number of 
fbdev drivers with deferred I/O contain similar code and the fbdev 
module should provide us with a helper. (I think I even had some patches 
somewhere.)

Best regards
Thomas

>   
>   	if ((y2 - y1) == 1) {
>   		/*
>   		 * We've only written to a single scanline. Try to reduce
>   		 * the number of horizontal pixels that need an update.
>   		 */
> -		off_t bit_off = (off % info->fix.line_length) * 8;
> -		off_t bit_end = (end % info->fix.line_length) * 8;
> +		off_t bit_off = (off % stride) * 8;
> +		off_t bit_end = (end % stride) * 8;
>   
> -		x1 = bit_off / info->var.bits_per_pixel;
> -		x2 = DIV_ROUND_UP(bit_end, info->var.bits_per_pixel);
> +		x1 = bit_off / bpp;
> +		x2 = DIV_ROUND_UP(bit_end, bpp);
>   	}
>   
>   	drm_rect_init(clip, x1, y1, x2 - x1, y2 - y1);
> 
>>
>>>>>>>> +  screen_size = sizes->surface_height * buffer->fb->pitches[0];
>>>>>>>> +
>>>>>>>>              screen_buffer = vzalloc(screen_size);
>>>>>>>>              if (!screen_buffer) {
>>>>>>>>                      ret = -ENOMEM;
>>>>>>> Cheers, Daniel
>>>>>>>
>>>>>>>> --
>>>>>>>> 2.25.1
>>>>>>>>
>>>
>>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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