Postfix module - Mailman wrapper - Couldn't write data/aliases.db and data/virtual-mailman.db files

Bug #1696066 reported by Laurent Declercq on 2017-06-06
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
GNU Mailman
Medium
Mark Sapiro
mailman (Debian)
New
Undecided
Unassigned
mailman (Ubuntu)
Undecided
Unassigned

Bug Description

Dear project leader

At least in version 2.1.23, there is a bug regarding permissions set for Mailman data/aliases table and Mailman data/virtual-mailman map when these files are created from scratch.

Here I describe the current behavior for the Mailman data/aliases table only but the problem is identical for the Mailman data/virtual-mailman map.

In order, the following conditions have to be met:

- Postfix need read access to the aliases.db file
- Mailman like to be owner of those files and the Mailman group needs write access to them

I. Postfix needs a read access to the aliases.db file

We can either set permissions as 0660 and add postfix user to mailman group (what I've done), or set the permissions as 0664

II. Mailman group needs a write access to those files at any time

The following behavior has been observed:

When creating a new list on command line, using bin/newlist script as follow:

    # newlist -u virtualhost foobar

the files will be created as follow:

-rw-rw---- 1 root list aliases
-rw-r----- 1 root list aliases.db

The same thing has been observed when recreating the file from scratch using bin/genaliases:

-rw-rw---- 1 root list aliases
-rw-r----- 1 root list aliases.db

Note that in both cases, files were not present. Thus, they were created from scratch.

As you can see here, the Mailman data/aliases file is created with the expected group and permissions but the data/aliases.db file is only writable by owner. From the POSTALIAS(1) command point of view, that is the expected behavior: The file is created with the same group and other read permissions as their source file.

The problem here is that with those permissions, creating a list through Mailman interface later on will result in a permissions denied error because the Mailman group, through the wrapper, cannot write (update) the aliases.db file (no write permissions).

That is really a problem. Of course, one can just pre-create the files as follow:

# cd /var/lib/mailman
# sg list -c "touch data/aliases && postalias data/aliases"
# chmod 0660 data/aliases*

but that seem tedious. What if at some point (for any reason), the files get recreated from scratch?

So, from my point of view, the MTA/Postfix.py module should always set correct permissions on *.db file, to be sure that Mailman group has write permissions, at least when the files are created from scratch. Eg:

IF NOT EXISTS aliases:
   Touch data/aliases data/aliases.db with correct permissions (066x)
   Add alias entries into aliases as usually
   Run POSTALIAS(1) command as usually

Then, we are fine.

Thank you.

Related branches

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Mark Sapiro (msapiro) wrote :

There is another issue not mentioned in the original report and that is that aliases.db must be owned by the Mailman user so Postfix runs the pipe as the Mailman user and group.

bin/check_perms would check/fix this and also ensure the mode is at least 0660, but I've gone a step further and now ensure these things at the time the postalias and postmap commands are run and also ensure the mode is at least 0664 so Postfix doesn't need to be in Mailman's group.

Changed in mailman:
assignee: nobody → Mark Sapiro (msapiro)
importance: Undecided → Medium
milestone: none → 2.1.25
status: New → Fix Committed
Laurent Declercq (l-declercq) wrote :

@msapiro

I can confirm that the fixes solve the problems.

Thank you for your involvement here. That is much appreciated.

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