[PATCH] drm/virtio: Fix GEM handle creation UAF

[PATCH] drm/virtio: Fix GEM handle creation UAF

[Rob Clark]

From: Rob Clark <robdclark@chromium.org>

Userspace can guess the handle value and try to race GEM object creation
with handle close, resulting in a use-after-free if we dereference the
object after dropping the handle's reference.  For that reason, dropping
the handle's reference must be done *after* we are done dereferencing
the object.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index a5cccccb4998..f1c55c1630ca 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -366,10 +366,18 @@ static int virtio_gpu_resource_create_ioctl(struct drm_device *dev, void *data,
 		drm_gem_object_release(obj);
 		return ret;
 	}
-	drm_gem_object_put(obj);
 
 	rc->res_handle = qobj->hw_res_handle; /* similiar to a VM address */
 	rc->bo_handle = handle;
+
+	/*
+	 * The handle owns the reference now.  But we must drop our
+	 * remaining reference *after* we no longer need to dereference
+	 * the obj.  Otherwise userspace could guess the handle and
+	 * race closing it from another thread.
+	 */
+	drm_gem_object_put(obj);
+
 	return 0;
 }
 
@@ -731,11 +739,18 @@ static int virtio_gpu_resource_create_blob_ioctl(struct drm_device *dev,
 		drm_gem_object_release(obj);
 		return ret;
 	}
-	drm_gem_object_put(obj);
 
 	rc_blob->res_handle = bo->hw_res_handle;
 	rc_blob->bo_handle = handle;
 
+	/*
+	 * The handle owns the reference now.  But we must drop our
+	 * remaining reference *after* we no longer need to dereference
+	 * the obj.  Otherwise userspace could guess the handle and
+	 * race closing it from another thread.
+	 */
+	drm_gem_object_put(obj);
+
 	return 0;
 }
 
-- 
2.38.1

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH] drm/virtio: Fix GEM handle creation UAF

[Chia-I Wu]

On Fri, Dec 16, 2022 at 3:33 PM Rob Clark <robdclark@gmail.com> wrote:
>
> From: Rob Clark <robdclark@chromium.org>
>
> Userspace can guess the handle value and try to race GEM object creation
> with handle close, resulting in a use-after-free if we dereference the
> object after dropping the handle's reference.  For that reason, dropping
> the handle's reference must be done *after* we are done dereferencing
> the object.
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH] drm/virtio: Fix GEM handle creation UAF

[Rob Clark]

On Mon, Jan 9, 2023 at 3:28 PM Dmitry Osipenko
<dmitry.osipenko@collabora.com> wrote:
>
> On 12/17/22 02:33, Rob Clark wrote:
> > From: Rob Clark <robdclark@chromium.org>
> >
> > Userspace can guess the handle value and try to race GEM object creation
> > with handle close, resulting in a use-after-free if we dereference the
> > object after dropping the handle's reference.  For that reason, dropping
> > the handle's reference must be done *after* we are done dereferencing
> > the object.
> >
> > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > ---
> >  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 19 +++++++++++++++++--
> >  1 file changed, 17 insertions(+), 2 deletions(-)
>
> Added fixes/stable tags and applied this virtio-gpu patch to misc-fixes.
> The Panfrost patch is untouched.

Thanks.. the panfrost patch was not intended to be part of the same
series (but apparently that is what happens when I send them at the
same time), and was superceded by a patch from Steven Price (commit
4217c6ac8174 ("drm/panfrost: Fix GEM handle creation ref-counting")
already applied to misc-fixes

BR,
-R
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization