[Dovecot] Dovecot allows creation of folders outside of a user's directory

[Christoph Bußenius]

Hi,

in our dovecot 2.0 setup with shared folders, users can make dovecot 
create directories outside their mail directory.  Which is a bit scary imho.

The following command:

. create inbox.shared.abc123

or even

. create "inbox.shared.strange &ANY- characters"

-- even though it will fail with a "permission denied" error -- will 
create a directory like "/mail/users/strange &ANY- characters".  That 
directory will only contain a subdirectory "Maildir" and therein 
dovecot-acl-list.

I think basically the reason for this behaviour is that Dovecot checks 
whether the directory has enough ACLs for the user to access it, and 
auto-creates the directory in the process.  Is there way to avoid this 
auto-creation - or maybe a way to make Dovecot check whether the 
directory name is an existing username?

Here's a config to reproduce this:

# 2.0.19: /usr/local/dovecot/etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-35-server x86_64 Ubuntu 10.04.4 LTS
auth_username_format = %Ln
disable_plaintext_auth = no
mail_gid = vmail
mail_home = /mail/users/%u
mail_location = maildir:~/Maildir
mail_plugins = " acl"
mail_uid = vmail
maildir_very_dirty_syncs = yes
namespace default {
   inbox = yes
   location =
   prefix = INBOX.
   separator = .
   type = private
}
namespace sharedns {
   inbox = no
   list = children
   location = maildir:/mail/users/%%u/Maildir
   prefix = INBOX.shared.%%u.
   separator = .
   subscriptions = no
   type = shared
}
passdb {
   args = /usr/local/dovecot/etc/dovecot/users
   driver = passwd-file
}
plugin {
   acl = vfile:/usr/local/dovecot/etc/dovecot/global-acls:cache_secs=300
   acl_shared_dict = file:/mail/vmail/shared-mailboxes.db
}
service auth {
   unix_listener auth-userdb {
     group = vmail
     mode = 0660
   }
}
ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_key = </etc/ssl/private/dovecot.pem
syslog_facility = local6
userdb {
   args = /usr/local/dovecot/etc/dovecot/users
   driver = passwd-file
}
protocol lmtp {
   mail_plugins = " sieve"
}
protocol imap {
   imap_client_workarounds = tb-extra-mailbox-sep
   mail_plugins = " acl imap_acl"
}


Content of the "users" file looks like this:

user1:{plain}(hidden):::user1:/mail/users/user1::
user2:{plain}(hidden):::user2:/mail/users/user2::
testuser:{plain}(hidden):::testuser:/mail/users/testuser::

Cheers,
Christoph

-- 
Christoph Bußenius
Rechnerbetriebsgruppe der Fakultäten Informatik und Mathematik
Technische Universität München
+49 89-289-18519 <> Raum 00.05.055 <> Boltzmannstr. 3 <> Garching