linux-kernel - Re: [PATCH] fbdev: efifb: Fix a use-after-free due early fb

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Date:   Sat, 7 May 2022 09:20:53 -0700
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Peter Jones <pjones@...hat.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Helge Deller <deller@....de>
Subject: Re: [PATCH] fbdev: efifb: Fix a use-after-free due early fb_info
 cleanup

On Fri, May 06, 2022 at 03:22:25PM +0200, Javier Martinez Canillas wrote:
>Commit d258d00fb9c7 ("fbdev: efifb: Cleanup fb_info in .fb_destroy rather
>than .remove") attempted to fix a use-after-free error due driver freeing
>the fb_info in the .remove handler instead of doing it in .fb_destroy.
>
>But ironically that change introduced yet another use-after-free since the
>fb_info was still used after the free.
>
>This should fix for good by freeing the fb_info at the end of the handler.
>
>Fixes: d258d00fb9c7 ("fbdev: efifb: Cleanup fb_info in .fb_destroy rather than .remove")

are these patches going through any CI before being applied? Maybe would
be a good idea to cc intel-gfx mailing list on these fixes to have Intel
CI to pick them up for some tests?

pushed to drm-misc-fixes where the previous patch was applied.

thanks
LUcas De Marchi

>Reported-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
>Reported-by: Andrzej Hajda <andrzej.hajda@...el.com>
>Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
>---
>
> drivers/video/fbdev/efifb.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
>index cfa3dc0b4eee..b3d5f884c544 100644
>--- a/drivers/video/fbdev/efifb.c
>+++ b/drivers/video/fbdev/efifb.c
>@@ -259,12 +259,12 @@ static void efifb_destroy(struct fb_info *info)
> 			memunmap(info->screen_base);
> 	}
>
>-	framebuffer_release(info);
>-
> 	if (request_mem_succeeded)
> 		release_mem_region(info->apertures->ranges[0].base,
> 				   info->apertures->ranges[0].size);
> 	fb_dealloc_cmap(&info->cmap);
>+
>+	framebuffer_release(info);
> }
>
> static const struct fb_ops efifb_ops = {
>-- 
>2.35.1
>