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 <tzimmermann@xxxxxxx> 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@xxxxxxxxxx>
Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
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
Attachment:
OpenPGP_signature
Description: OpenPGP digital signature