vat: fix static analysis warning

Type: fix
Ticket: VPP-1837

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: Ia46f865082dcf0cf06af99a7c958c4a5b02193ce
diff --git a/src/vat/json_format.h b/src/vat/json_format.h
index 154fb3d..d2fab90 100644
--- a/src/vat/json_format.h
+++ b/src/vat/json_format.h
@@ -93,8 +93,9 @@
 vat_json_set_string_copy (vat_json_node_t * json, const u8 * str)
 {
   u8 *ns = NULL;
-  vec_validate (ns, strlen ((const char *) str));
-  strcpy ((char *) ns, (const char *) str);
+  int len = strlen ((const char *) str);
+  vec_validate (ns, len);
+  strncpy ((char *) ns, (const char *) str, len + 1);
   vec_add1 (ns, '\0');
   vat_json_set_string (json, ns);
 }