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 <[email protected]>
---
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;
}
--
2.33.0.800.g4c38ced690-goog
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 <[email protected]>
Acked-by: Thomas Zimmermann <[email protected]>
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
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.
On Thu, 30 Sept 2021 at 17:21, Thomas Zimmermann <[email protected]> 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 <[email protected]>
>
> Acked-by: Thomas Zimmermann <[email protected]>
>
> 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
--
Anand K. Mistry
Software Engineer
Google Australia
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 <[email protected]> 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 <[email protected]>
>>
>> Acked-by: Thomas Zimmermann <[email protected]>
>>
>> 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