linux-kernel - [PATCH 5.17 605/772] video: fbdev: vesafb: Fix a use-after-free due early fb

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Message-Id: <20220607165006.768209733@linuxfoundation.org>
Date:   Tue,  7 Jun 2022 19:03:17 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pascal Ernster <dri-devel@...dfalcon.net>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Helge Deller <deller@....de>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.17 605/772] video: fbdev: vesafb: Fix a use-after-free due early fb_info cleanup

From: Javier Martinez Canillas <javierm@...hat.com>

[ Upstream commit acde4003efc16480375543638484d8f13f2e99a3 ]

Commit b3c9a924aab6 ("fbdev: vesafb: Cleanup fb_info in .fb_destroy rather
than .remove") fixed a use-after-free error due the vesafb driver freeing
the fb_info in the .remove handler instead of doing it in .fb_destroy.

This can happen if the .fb_destroy callback is executed after the .remove
callback, since the former tries to access a pointer freed by the latter.

But that change didn't take into account that another possible scenario is
that .fb_destroy is called before the .remove callback. For example, if no
process has the fbdev chardev opened by the time the driver is removed.

If that's the case, fb_info will be freed when unregister_framebuffer() is
called, making the fb_info pointer accessed in vesafb_remove() after that
to no longer be valid.

To prevent that, move the expression containing the info->par to happen
before the unregister_framebuffer() function call.

Fixes: b3c9a924aab6 ("fbdev: vesafb: Cleanup fb_info in .fb_destroy rather than .remove")
Reported-by: Pascal Ernster <dri-devel@...dfalcon.net>
Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
Tested-by: Pascal Ernster <dri-devel@...dfalcon.net>
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/video/fbdev/vesafb.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/video/fbdev/vesafb.c b/drivers/video/fbdev/vesafb.c
index e25e8de5ff67..929d4775cb4b 100644
--- a/drivers/video/fbdev/vesafb.c
+++ b/drivers/video/fbdev/vesafb.c
@@ -490,11 +490,12 @@ static int vesafb_remove(struct platform_device *pdev)
 {
 	struct fb_info *info = platform_get_drvdata(pdev);

-	/* vesafb_destroy takes care of info cleanup */
-	unregister_framebuffer(info);
 	if (((struct vesafb_par *)(info->par))->region)
 		release_region(0x3c0, 32);

+	/* vesafb_destroy takes care of info cleanup */
+	unregister_framebuffer(info);
+
 	return 0;
 }

-- 
2.35.1