FAILED: patch "[PATCH] drm/virtio: Fix GEM handle creation UAF" failed to apply to 4.19-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

Possible dependencies:

52531258318e ("drm/virtio: Fix GEM handle creation UAF")
897b4d1acaf5 ("drm/virtio: implement blob resources: resource create blob ioctl")
16845c5d5409 ("drm/virtio: implement blob resources: implement vram object")
6076a9711dc5 ("drm/virtio: implement blob resources: probe for host visible region")
6815cfe602d0 ("drm/virtio: implement blob resources: probe for the feature.")
30172efbfb84 ("drm/virtio: blob prep: refactor getting pages and attaching backing")
deb2464e4c6d ("drm/virtio: report uuid in debugfs")
c84adb304c10 ("drm/virtio: Support virtgpu exported resources")
0a19b068acc4 ("Merge tag 'drm-misc-next-2020-06-19' of git://anongit.freedesktop.org/drm/drm-misc into drm-next")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 52531258318ed59a2dc5a43df2eaf0eb1d65438e Mon Sep 17 00:00:00 2001
From: Rob Clark <robdclark@xxxxxxxxxxxx>
Date: Fri, 16 Dec 2022 15:33:55 -0800
Subject: [PATCH] drm/virtio: Fix GEM handle creation UAF

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@xxxxxxxxxxxx>
Reviewed-by: Chia-I Wu <olvaffe@xxxxxxxxx>
Fixes: 62fb7a5e1096 ("virtio-gpu: add 3d/virgl support")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20221216233355.542197-2-robdclark@xxxxxxxxx

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index 5d05093014ac..9f4a90493aea 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -358,10 +358,18 @@ 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;
 }
 
@@ -723,11 +731,18 @@ 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;
 }