misc: mic: Fix for double fetch security bug in VOP driver

The MIC VOP driver does two successive reads from user space to read a
variable length data structure. Kernel memory corruption can result if
the data structure changes between the two reads. This patch disallows
the chance of this happening.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=116651
Reported by: Pengfei Wang <[e-mail]>
Reviewed-by: Sudeep Dutt <[e-mail]>
Signed-off-by: Ashutosh Dixit <[e-mail]>
Cc: stable <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/mic/vop/vop_vringh.c

···
 			ret = -EFAULT;
 			goto free_ret;
 		}
+		/* Ensure desc has not changed between the two reads */
+		if (memcmp(&dd, dd_config, sizeof(dd))) {
+			ret = -EINVAL;
+			goto free_ret;
+		}
 		mutex_lock(&vdev->vdev_mutex);
 		mutex_lock(&vi->vop_mutex);
 		ret = vop_virtio_add_device(vdev, dd_config);