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SubjectRe: [PATCH] drm/fbdev-generic: fix potential out-of-bounds access
From
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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