linux-kernel - [PATCH v3 2/4] fbdev: simplefb: Cleanup fb_info in .fb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri,  6 May 2022 00:04:56 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Helge Deller <deller@....de>,
        Hans de Goede <hdegoede@...hat.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: [PATCH v3 2/4] fbdev: simplefb: Cleanup fb_info in .fb_destroy rather than .remove

The driver is calling framebuffer_release() in its .remove callback, but
this will cause the struct fb_info to be freed too early. Since it could
be that a reference is still hold to it if user-space opened the fbdev.

This would lead to a use-after-free error if the framebuffer device was
unregistered but later a user-space process tries to close the fbdev fd.

To prevent this, move the framebuffer_release() call to fb_ops.fb_destroy
instead of doing it in the driver's .remove callback.

Strictly speaking, the code flow in the driver is still wrong because all
the hardware cleanupd (i.e: iounmap) should be done in .remove while the
software cleanup (i.e: releasing the framebuffer) should be done in the
.fb_destroy handler. But this at least makes to match the behavior before
commit 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal").

Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal")
Suggested-by: Daniel Vetter <daniel.vetter@...ll.ch>
Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
---

(no changes since v1)

 drivers/video/fbdev/simplefb.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
index 94fc9c6d0411..2c198561c338 100644
--- a/drivers/video/fbdev/simplefb.c
+++ b/drivers/video/fbdev/simplefb.c
@@ -84,6 +84,10 @@ struct simplefb_par {
 static void simplefb_clocks_destroy(struct simplefb_par *par);
 static void simplefb_regulators_destroy(struct simplefb_par *par);
 
+/*
+ * fb_ops.fb_destroy is called by the last put_fb_info() call at the end
+ * of unregister_framebuffer() or fb_release(). Do any cleanup here.
+ */
 static void simplefb_destroy(struct fb_info *info)
 {
 	struct simplefb_par *par = info->par;
@@ -94,6 +98,8 @@ static void simplefb_destroy(struct fb_info *info)
 	if (info->screen_base)
 		iounmap(info->screen_base);
 
+	framebuffer_release(info);
+
 	if (mem)
 		release_mem_region(mem->start, resource_size(mem));
 }
@@ -545,8 +551,8 @@ static int simplefb_remove(struct platform_device *pdev)
 {
 	struct fb_info *info = platform_get_drvdata(pdev);
 
+	/* simplefb_destroy takes care of info cleanup */
 	unregister_framebuffer(info);
-	framebuffer_release(info);
 
 	return 0;
 }
-- 
2.35.1