The event received should be checked to be #PF before
accessing its other arguments.

[ Mike:
    Well, looking forward to see non-cooperative userfaultfd patches in kernel
    we should have something like

    static int handle_uffd_enent(struct lazy_pages_info *lpi)
    {
    	read(&msg...);

    	switch (msg.event) {
    	case UFFD_EVENT_PAGEFAULT:
    		handle_pagefault(lpi, msg);
    		break;
    	default:
    		return -1;
    	}
    }

    But since this patch is anyway is a bugfix: <ack>
]

travis-ci: success for uffd: A set of improvements over criu/uffd.c
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>