Re: mail server recommendations?

From: Mark Johnston (mjohnston_at_skyweb.ca)
Date: 04/12/04

  • Next message: Miroslav Lachman: "Re: mail server recommendations?" 
    To: Miroslav Lachman <000.fbsd@quip.cz>
Date: Mon, 12 Apr 2004 15:27:46 -0500

    Miroslav Lachman <000.fbsd@quip.cz> wrote:
    > Hi, I am running similar configuration on several machines (Postfix +
    > Courier-IMAP [with POP3ssl/IMAP4ssl] + MySQL). I have a guestion about
    > one general difference - unique UID / GID for each user. I guess it
    > provide more security, but also some troubles. If all virtual users
    > (stored in MySQL) have same UID/GID, postfix can be configured to create
    > maildirs itself with first incoming message. If each user has unique
    > UID, maildirs must be created manualy (or from shellscript) and chowned
    > to UID/GID.

    Exactly - that's the tradeoff.

    > My question: "If all virtual users have same UID/GID, is there some real
    > security risk?".

    Sharing UIDs and GIDs can have good or bad effects on security. On a server
    with no users logging in, like mine, it's moot; nobody (well, nobody who
    hasn't compromised the server) can get at the maildir storage on disk, so
    nobody (ditto) can play with the mailboxes. On a server where users do log
    in, you can go two routes:

    - Unique UIDs/GIDs. This makes things more convenient for the user, since
    they can use mail clients on the server and get right at their mail. If you
    want to have local mail clients work at all, you have to do this.

    - Shared UID/GID. In this case, the user can't get at their own maildir, and
    they'll have to use LDAP/POP3 over loopback to read their mail. It does make
    management easier, though.

    It sounds to me like you're working with a server where users don't log in,
    since you're using MySQL to manage user accounts. In that case, unique UIDs
    buy you essentially nothing.

    > I'll be glad to read if same UID/GID is secure or not, because I am
    > writing webbased administration tool in PHP and main problem is creation
    > of maildirs for new accounts. Same UID/GID could solve my problem.

    The only time that unique UIDs and GIDs are useful is when the user will be
    logging in locally, so you can just look in /etc/passwd, find the user's UID,
    and create the maildir with that. If the user doesn't have a system account,
    you've got no reason to start making up UIDs to give them one; just share a
    single UID.

    > PS: sorry for my bad english and a little offtopic message

    Since you say "offtopic", I assume you intended this for the freebsd-isp list,
    instead of private mail. I've taken the liberty of including the list in the
    Cc again, since security advice like this shouldn't go unreviewed. :) You
    might also want to move this thread to freebsd-security@freebsd.org, to reach
    people with more security know-how.

    > PPS: I'll publish webbased administration tool on sourceforge.net after
    > completition
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  • Next message: Miroslav Lachman: "Re: mail server recommendations?"

    Relevant Pages

    • Re: mail server recommendations?
      ... >>maildirs itself with first incoming message. ... > Sharing UIDs and GIDs can have good or bad effects on security. ... > hasn't compromised the server) can get at the maildir storage on disk, ... In that case, unique UIDs ...
      (freebsd-isp)
    • fwd: mail server recommendations?
      ... Postfix virtual users accounts. ... >> provide more security, but also some troubles. ... > Sharing UIDs and GIDs can have good or bad effects on security. ... nobody who hasn't compromised the server) can get at the maildir storage ...
      (FreeBSD-Security)