linux-kernel - Re: [PATCH] drm/prime: Fix use after free in mmap with drm_gem_ttm

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]

Message-ID: <17d63b06-d1bd-85ab-92d3-71fa236b9493@suse.de>
Date:   Thu, 30 Sep 2021 09:21:02 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Anand K Mistry <amistry@...gle.com>,
        dri-devel@...ts.freedesktop.org
Cc:     nartemiev@...gle.com, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/prime: Fix use after free in mmap with
 drm_gem_ttm_mmap

Hi

Am 30.09.21 um 01:00 schrieb Anand K Mistry:
> drm_gem_ttm_mmap() drops a reference to the gem object on success. If
> the gem object's refcount == 1 on entry to drm_gem_prime_mmap(), that
> drop will free the gem object, and the subsequent drm_gem_object_get()
> will be a UAF. Fix by grabbing a reference before calling the mmap
> helper.
> 
> This issue was forseen when the reference dropping was adding in
> commit 9786b65bc61ac ("drm/ttm: fix mmap refcounting"):
>    "For that to work properly the drm_gem_object_get() call in
>    drm_gem_ttm_mmap() must be moved so it happens before calling
>    obj->funcs->mmap(), otherwise the gem refcount would go down
>    to zero."
> 
> Signed-off-by: Anand K Mistry <amistry@...gle.com>

Acked-by: Thomas Zimmermann <tzimmermann@...e.de>

This looks fine to me, but it affects many drivers. Let's maybe wait a 
bit if more reviews come it.

Best regards
Thomas

> ---
> 
>   drivers/gpu/drm/drm_prime.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 2a54f86856af..e1854fd24bb0 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -719,11 +719,13 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
>   	if (obj->funcs && obj->funcs->mmap) {
>   		vma->vm_ops = obj->funcs->vm_ops;
>   
> +		drm_gem_object_get(obj);
>   		ret = obj->funcs->mmap(obj, vma);
> -		if (ret)
> +		if (ret) {
> +			drm_gem_object_put(obj);
>   			return ret;
> +		}
>   		vma->vm_private_data = obj;
> -		drm_gem_object_get(obj);
>   		return 0;
>   	}
>   
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

Download attachment "OpenPGP_signature" of type "application/pgp-signature" (841 bytes)