[FIXED JENKINS-8802] Allow use of FilePath.validateFileMask and validateFilePath

from global level (not in a job config page).  Require admin permission for this.
Based on patch from bap.

core/src/main/java/hudson/FilePath.java

@@ -39,6 +39,7 @@ import hudson.remoting.Pipe;
 import hudson.remoting.RemoteOutputStream;
 import hudson.remoting.VirtualChannel;
 import hudson.remoting.RemoteInputStream;
+import hudson.security.AccessControlled;
 import hudson.util.DirScanner;
 import hudson.util.IOException2;
 import hudson.util.HeadBufferingStream;
@@ -1777,12 +1778,12 @@ public final class FilePath implements Serializable {
 
     /**
      * Checks the GLOB-style file mask. See {@link #validateAntFileMask(String)}.
-     * Requires configure permission on ancestor AbstractProject object in request.
+     * Requires configure permission on ancestor AbstractProject object in request,
+     * or admin permission if no such ancestor is found.
      * @since 1.294
      */
     public FormValidation validateFileMask(String value, boolean errorIfNotExist) throws IOException {
-        AbstractProject subject = Stapler.getCurrentRequest().findAncestorObject(AbstractProject.class);
-        subject.checkPermission(Item.CONFIGURE);
+        checkPermissionForValidate();
 
         value = fixEmpty(value);
         if(value==null)
@@ -1802,7 +1803,8 @@ public final class FilePath implements Serializable {
 
     /**
      * Validates a relative file path from this {@link FilePath}.
-     * Requires configure permission on ancestor AbstractProject object in request.
+     * Requires configure permission on ancestor AbstractProject object in request,
+     * or admin permission if no such ancestor is found.
      *
      * @param value
      *      The relative path being validated.
@@ -1813,8 +1815,7 @@ public final class FilePath implements Serializable {
      *      Otherwise, the relative path is expected to be pointing to a directory.
      */
     public FormValidation validateRelativePath(String value, boolean errorIfNotExist, boolean expectingFile) throws IOException {
-        AbstractProject subject = Stapler.getCurrentRequest().findAncestorObject(AbstractProject.class);
-        subject.checkPermission(Item.CONFIGURE);
+        checkPermissionForValidate();
 
         value = fixEmpty(value);
 
@@ -1852,6 +1853,14 @@ public final class FilePath implements Serializable {
         }
     }
 
+    private static void checkPermissionForValidate() {
+        AccessControlled subject = Stapler.getCurrentRequest().findAncestorObject(AbstractProject.class);
+        if (subject == null)
+            Hudson.getInstance().checkPermission(Hudson.ADMINISTER);
+        else
+            subject.checkPermission(Item.CONFIGURE);
+    }
+
     /**
      * A convenience method over {@link #validateRelativePath(String, boolean, boolean)}.
      */