Item1527: RedirectPlugin can cause infinite loop

RedirectPlugin needs protection from redirect loops. here's the simplest case:

TopicA: REDIRECT{TopicB} TopicB: REDIRECT{TopicA}

this could be solved by either of these solutions

• have a maximum redirect count
• detect circular references (that is, if you're been redirected to a topic that you've already "seen")

-- WillNorris - 25 Apr 2009

I've been working in this task and I think that we can solve this by using redirectedfrom parameter to keep a history of topics that we had already seen. Thus, if you're been to a topic that you've already 'seen' we stop the redirection (as proposed by Will).

In order to keep the history of visited topics (using some redirectedfrom URL parameters) we need to deal with multivalued CGI parameters. Currently the plugin does not handly such feature. So I needed to modify the plugin according.

Here's a patch that I made from http://svn.foswiki.org/trunk/RedirectPlugin:

Index: lib/Foswiki/Plugins/RedirectPlugin.pm
===================================================================
--- lib/Foswiki/Plugins/RedirectPlugin.pm   (revision 7221)
+++ lib/Foswiki/Plugins/RedirectPlugin.pm   (working copy)
@@ -73,8 +73,10 @@
         my $queryString = "";
         my $param;
         foreach my $param ( $query->param ) {
-            $queryString .= "&" if $queryString;
-            $queryString .= "$param=" . $query->param("$param");
+            foreach ( $query->param("$param") ) {
+                $queryString .= "&" if $queryString;
+                $queryString .= "$param=" . $_;
+            }
         }
 
         # do not redirect when param "redirect=no" is passed
@@ -103,6 +105,11 @@
             $topicLocation = "$newWeb.$newTopic";
         }
 
+        return "%BR% %RED% Cannot redirect to current topic %ENDCOLOR%"
+          if ( $topicLocation eq "$web.$topic" );
+        return "%BR% %RED% Cannot redirect to an already visited topic %ENDCOLOR%"
+          if ( $queryString =~ /redirectedfrom=$topicLocation/ );
+
         unless ($dontCheckDestinationExists) { 
        if ( !Foswiki::Func::topicExists( undef, $topicLocation ) ) {
       return

Testing environment :

• In Sandbox.PageA, use %REDIRECT{PageA}%: should't work.
• In Sandbox.PageA, use %REDIRECT{PageB}%; in Sandbox.PageB use %REDIRECT{PageC}%; in Sandbox.PageC use %REDIRECT{PageA}%: should't work.
• In Sandbox.PageA, use %REDIRECT{OtherWeb.TestX}%; in OtherWeb.TestX use %REDIRECT{Sandbox.PageA}%: should't work.
• Anything else: should work.

However, I've no idea how to handle cases where we redirect to an URL (the plugin does not keep the redirectedfrom parameter).

So, that's it. I prefered don't commit my changes and wait for some feedbacks. After someone review, I can commit my changes (or no... :-)).

Thanks.

-- ItaloValcy - 19 Apr 2010

The bug was solved at 1.1 release of RedirectPlugin. Please check it out.

-- ItaloValcy - 26 Jun 2010