Enhance allowed script dir to not allow relative pathnames.

When users start using releative pathnames it becomes hard to determine
if a path is within a certain allowed path setting without reverting to
more drastic measures. So we just don't allow relative pathnames for
scripts when using the allowed script dir feature.

src/lib/runscript.c

@@ -114,6 +114,16 @@ static inline bool script_dir_allowed(JCR *jcr, RUNSCRIPT *script, alist *allowe
       *bp = '\0';
    }
 
+   /*
+    * Make sure there are no relative path elements in script dir by which the
+    * user tries to escape the allowed dir checking. For scripts we only allow
+    * absolute paths.
+    */
+   if (strstr(script_dir.c_str(), "..")) {
+      Dmsg1(200, "script_dir_allowed: relative pathnames not allowed: %s\n", script_dir.c_str());
+      return false;
+   }
+
    /*
     * Match the path the script is in against the list of allowed script directories.
     */
@@ -124,6 +134,9 @@ static inline bool script_dir_allowed(JCR *jcr, RUNSCRIPT *script, alist *allowe
       }
    }
 
+   Dmsg2(200, "script_dir_allowed: script %s %s allowed by Allowed Script Dir setting",
+         script->command, (allowed) ? "" : "NOT");
+
    return allowed;
 }