--- sys/geom/virstor/g_virstor.c	2008-11-22 14:40:22.000000000 +0800
+++ /var/current/mysrc/sys/geom/virstor/g_virstor.c	2008-11-25 09:59:25.000000000 +0800
@@ -565,6 +565,10 @@
 
 		sprintf(param, "arg%d", i);
 		prov_name = gctl_get_asciiparam(req, param);
+		if (prov_name == NULL) {
+			gctl_error(req, "Error fetching argument '%s'", param);
+			return;
+		}
 		if (strncmp(prov_name, _PATH_DEV, strlen(_PATH_DEV)) == 0)
 			prov_name += strlen(_PATH_DEV);