i915_gem_userptr_get_pages in drivers/gpu/drm/i915/i915_gem_userptr.c in the Linux kernel 4.15.0 on Ubuntu 18.04.2 allows local users to cause a denial of service (NULL pointer dereference and BUG) or possibly have unspecified other impact via crafted ioctl calls to /dev/dri/card0.
CVE Vulnerability