[Samba] Users can delete a file they don't have permition in the public share

[Bruno Gimenes Pereti]

Hi!

I'll try to explain all the situation to help you understand the problem. I 
have a Samba 3.0.4 + LDAP + ACL PDC and I use poledit to define the 
background image of the users to \\PDC\public\background.bmp, this file:

-rw-r--r--    1 Administrator root       787510 09-23 17:34 background.bmp

Yes, the acl is not used in this file. This is the public share in smb.conf:

[public]
   comment = Compartilhamento Público
   path = /home/samba/public
#   public = yes
#   guest ok = yes
   writable = yes
   create mask = 0666
   directory mask = 777
   printable = no
   invalid users = prova

yesterday one of the users (students) deleted this file and I thought they 
shouldn't have permission to do this because they don't have write 
permission in the file.

I tried every thing I know about permition (that's not much) and couldn't 
find a solution. What can I do to prevent the students to delete this file?

Thanks,
Bruno Pereti.