Re: [PATCH] drm/fb-helper: Fix out-of-bounds access

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 29.06.22 um 20:17 schrieb Geert Uytterhoeven:
>      Hi Thomas,
>
> On Tue, 21 Jun 2022, Thomas Zimmermann wrote:
> > Clip memory range to screen-buffer size to avoid out-of-bounds access
> > in fbdev deferred I/O's damage handling.
> >
> > Fbdev's deferred I/O can only track pages. From the range of pages, the
> > damage handler computes the clipping rectangle for the display update.
> > If the fbdev screen buffer ends near the beginning of a page, that page
> > could contain more scanlines. The damage handler would then track these
> > non-existing scanlines as dirty and provoke an out-of-bounds access
> > during the screen update. Hence, clip the maximum memory range to the
> > size of the screen buffer.
> >
> > While at it, rename the variables min/max to min_off/max_off in
> > drm_fb_helper_deferred_io(). This avoids confusion with the macros of
> > the same name.
> >
> > Reported-by: Nuno Gonçalves <nunojpg@xxxxxxxxx>
> > Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > Tested-by: Nuno Gonçalves <nunojpg@xxxxxxxxx>
> > Fixes: 67b723f5b742 ("drm/fb-helper: Calculate damaged area in 
> > separate helper")
>
> Thanks for your patch, which is now commit ae25885bdf59fde4
> ("drm/fb-helper: Fix out-of-bounds access") in drm-misc/for-linux-next.
>
> I had seen the crash before, but thought it was a bug in my wip
> atari-drm driver.  When diving deeper today, and consequently looking
> for recent changes to the damage helper, I found this commit in
> linux-next.
>
> With your patch instead of my own workaround I used this morning, [1]
> still works fine, so:
> Tested-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>.
> Reviewed-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>.

Great thanks a lot.

BTW, what's the status of the atari-drm driver?

Best regard
Thomas

> [1] [PATCH] drm/fb-helper: Remove helpers to change frame buffer config
>      
> https://lore.kernel.org/all/20220629105658.1373770-1-geert@xxxxxxxxxxxxxx
>
> Gr{oetje,eeting}s,
>
>                          Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- 
> geert@xxxxxxxxxxxxxx
>
> In personal conversations with technical people, I call myself a hacker. 
> But
> when I'm talking to journalists I just say "programmer" or something 
> like that.
>                                  -- Linus Torvalds

--
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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