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
| ||
|
Date: Thu, 5 May 2022 09:29:40 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Javier Martinez Canillas <javierm@...hat.com>,
linux-kernel@...r.kernel.org
Cc: linux-fbdev@...r.kernel.org,
Daniel Vetter <daniel.vetter@...ll.ch>,
Helge Deller <deller@....de>, dri-devel@...ts.freedesktop.org,
Hans de Goede <hdegoede@...hat.com>
Subject: Re: [PATCH 2/3] fbdev/simplefb: Cleanup fb_info in .fb_destroy rather
than .remove
Hi
Am 04.05.22 um 23:57 schrieb Javier Martinez Canillas:
> 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.
>
> The correct thing to do is to only unregister the framebuffer in the
> driver's .remove callback, but do any cleanup in the fb_ops.fb_destroy.
>
> Suggested-by: Daniel Vetter <daniel.vetter@...ll.ch>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
Please see my question below.
> ---
>
> 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));
The original problem with fbdev hot-unplug was that vmwgfx needed the
framebuffer region to be released. If we release it only after userspace
closed it's final file descriptor, vmwgfx could have already failed.
I still don't fully get why this code apparently works or at least
doesn't blow up occasionally. Any ideas?
Best regards
Thomas
> }
> @@ -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;
> }
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
Download attachment "OpenPGP_signature" of type "application/pgp-signature" (841 bytes)
Powered by blists - more mailing lists