Redmine

Hi
I design a new plugin for Redmine.
I have created a new Class : Meeting.
Each meeting can have an attachment. On my databse the container_type = 'Meeting' for this type of attachments.

I can save on the database the new attachment, but when i try to read it(e.g. : /attachments/21/pdf_final.pdf) I got a 403 error : "You are not authorized to access this page."

How can I change the rules in order to allow the user to read this attachment ?
I have looked around the attachments model and acts_as_attachable.rb but I can't find a solution.
For exemple, I didn't understand where is defined the permission to see (or not) an issue attachment.

Thanks for your help !