syz-manager: add a check for localhost

If localhost is not resolvable on a system, we might run into a loop
(for example in vm/vmimpl/UnusedTCPPort) or
fail later. Since syzkaller uses localhost (and not something like
127.0.0.1) it's way better to notify user earlier if their 'localhost' is
not configured correctly.

Signed-off-by: Ivan Gulakov <gulakov@amazon.com>

Author: p13l13d13

syz-manager/manager.go

@@ -242,6 +242,11 @@ func main() {
 }
 
 func RunManager(mode *Mode, cfg *mgrconfig.Config) {
+	// localhost is going to be used later, notify users
+	if _, err := net.LookupHost("localhost"); err != nil {
+		log.Fatalf("'localhost' is not resolving on this system, configure your DNS resolver")
+	}
+
 	var vmPool *vm.Pool
 	if !cfg.VMLess {
 		var err error