lkml.org 
[lkml]   [2021]   [Nov]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] drm/prime: Fix use after free in mmap with drm_gem_ttm_mmap
From
Hi

Am 03.11.21 um 01:12 schrieb Anand K. Mistry:
> Any movement on merging this patch? Not urgent on my end (we have this
> patch in our tree), but I think other amd users might run into this
> UAF.

Thanks for reminding. I've merged your patch into drm-misc-fixes.

Best regards
Thomas

>
> On Thu, 30 Sept 2021 at 17:21, Thomas Zimmermann <tzimmermann@suse.de> wrote:
>>
>> 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@google.com>
>>
>> Acked-by: Thomas Zimmermann <tzimmermann@suse.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
>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2021-11-03 09:55    [W:0.053 / U:0.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site