[bug 2.3.15] seeing user-shared mailboxes across different storage types requires manual change to subscriptions

[Michal Soltys]

Hi,

While I was checking old bug I once reported (that one seems to be 
fixed, https://www.dovecot.org/list/dovecot/2017-January/106593.html) I 
discovered another issue happening under current version when user 
sharing his mailbox (with Maildir storage) is not visible under user 
using mdbox (or sdbox, also tested) - unless subscriptions file is 
manually adjusted (after subscribing).

Consider following config:

# 2.3.15 (0503334ab1): /etc/dovecot/dovecot.conf
# OS: Linux 5.12.14-arch1-1 x86_64 Arch Linux btrfs
# Hostname: hakai
auth_debug = yes
auth_mechanisms = plain login
disable_plaintext_auth = no
first_valid_uid = 1
listen = *
mail_debug = yes
mail_gid = dovecot
mail_location = maildir:/var/mail1/%n/Maildir
mail_plugins = acl
mail_uid = dovecot
namespace {
   inbox = yes
   location =
   prefix =
   separator = /
   type = private
}
namespace shared1 {
   inbox = no
   list = yes
   location = maildir:%%h/Maildir/
   prefix = shared1/%%n/
   separator = /
   subscriptions = no
   type = shared
}
namespace shared2 {
   inbox = no
   list = yes
   location = mdbox:%%h/mdbox/
   prefix = shared2/%%n/
   separator = /
   subscriptions = no
   type = shared
}
passdb {
   args = /etc/dovecot/local-maildir
   driver = passwd-file
}
passdb {
   args = /etc/dovecot/local-mdbox
   driver = passwd-file
}
plugin {
   acl = vfile
   acl_shared_dict = file:/var/mail-data/shared-database/shared-mailboxes.db
}
protocols = imap
service auth {
   unix_listener auth-userdb {
     group = mail
     mode = 0660
     user = dovecot
   }
   user = dovecot
}
service imap-login {
   inet_listener imap {
     address = *
     port = 143
   }
   inet_listener imaps {
     address = *
     port = 993
   }
   user = dovecot
}
service imap {
   executable = /usr/lib/dovecot/imap
}
userdb {
   driver = prefetch
}
userdb {
   args = /etc/dovecot/local-maildir
   driver = passwd-file
}
userdb {
   args = /etc/dovecot/local-mdbox
   driver = passwd-file
}
protocol imap {
   mail_max_userip_connections = 100
   mail_plugins = acl imap_acl
}

/etc/dovecot/local-maildir:

user1:{PLAIN}test:::user1:/var/mail1/user1::userdb_mail=maildir:/var/mail1/user1/Maildir 
userdb_home=/var/mail1/user1
user2:{PLAIN}test:::user2:/var/mail1/user2::userdb_mail=maildir:/var/mail1/user2/Maildir 
userdb_home=/var/mail1/user2

/etc/dovecot/local-mdbox:

user3:{PLAIN}test:::user3:/var/mail2/user3::userdb_mail=mdbox:/var/mail2/user3/mdbox 
userdb_home=/var/mail2/user3

There are two shared namespaces - shared1 for Maildir mailboxes and 
shared2 for mdbox ones. 'user1' is sharing his 'qwer' folder to user3.

doveadm mailbox create -u user1 -s qwer
doveadm acl add -u user1 qwer user=user3 read lookup
doveadm mailbox subscribe -u user3 shared1/user1/qwer

This produces subscriptions file such as:

14:44 # cat /var/mail2/user3/mdbox/subscriptions
V       2

Trash
shared1	user1	qwer

With all that in place, 'qwer' won't be visible to user3. But if we 
change the 'shared1	user1	qwer' to shared1/user1/qwer - then everything 
will be working fine.

Sharing mdbox folder to maildir user (user3 -> user1) as well as maildir 
to maildir (user1 -> user2) works without issues.