Fix stack buffer overflow in var_subst() (dg_variables.c)

Agent-Logs-Url: https://github.com/tbamud/tbamud/sessions/5e320127-5bfa-499e-9776-e8a6cdd06bde

Co-authored-by: welcor <357770+welcor@users.noreply.github.com>

src/dg_variables.c

@@ -1636,6 +1636,13 @@ void var_subst(void *go, struct script_data *sc, trig_data *trig,
   int paren_count = 0;
   int dots = 0;
 
+  /* reject lines that would overflow our fixed-size buffers */
+  if (strnlen(line, MAX_INPUT_LENGTH) >= MAX_INPUT_LENGTH) {
+    script_log("Trigger VNum %d: variable substitution line too long, ignoring.", GET_TRIG_VNUM(trig));
+    *buf = '\0';
+    return;
+  }
+
   /* skip out if no %'s */
   if (!strchr(line, '%')) {
     strcpy(buf, line);