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

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Date:   Fri,  6 May 2022 15:22:25 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>, intel-gfx@...ts.freedesktop.org,
        Javier Martinez Canillas <javierm@...hat.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Helge Deller <deller@....de>, Peter Jones <pjones@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org
Subject: [PATCH] fbdev: efifb: Fix a use-after-free due early fb_info cleanup

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")
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