USN-3901-2: Linux kernel (HWE) vulnerabilities

USN-3901-1 fixed vulnerabilities in the Linux kernel for Ubuntu 18.04 LTS. This update provides the corresponding updates for the Linux Hardware Enablement (HWE) kernel from Ubuntu 18.04 LTS for Ubuntu 16.04 LTS. Jann Horn discovered that the userfaultd implementation in the Linux kernel did not properly restrict access to certain ioctls. A local attacker could use this possibly to modify files. (CVE-2018-18397) It was discovered that the crypto subsystem of the Linux kernel leaked uninitialized memory to user space in some situations. A local attacker could use this to expose sensitive information (kernel memory). (CVE-2018-19854) Jann Horn discovered a race condition in the fork() system call in the Linux kernel. A local attacker could use this to gain access to services that cache authorizations. (CVE-2019-6133)