Re: Mail delivery privileges (was: Solaris /usr/bin/mailx exploit)

From: Olaf Kirch (okirat_private)
Date: Fri May 18 2001 - 14:34:04 PDT

  • Next message: Steven M. Bellovin: "Re: Mail delivery privileges (was: Solaris /usr/bin/mailx exploit)"

    On Fri, May 18, 2001 at 11:18:51AM -0400, Wietse Venema wrote:
    > 2 - Lock file management. If mail is delivered as nobody:mail, then
    > /var/mail/username.lock files are owned by user nobody.  This means
    
    If you insist on using lock files for synchronization, that is. If you
    make sure all your MUAs and your MTA do proper flock locking, you get
    synchronization without the privilege issues surrounding lock files. That
    was in fact the least common denominator I found when I investigated
    something like 20 Unix mail software packages about three years ago
    (The major exception being wu-imap that's doing flock locking as an
    afterthought to dotlocking, and ignores any errors returned by flock).
    
    The only functionality you lose with flock is the ability to remotely
    mount your mail spool via NFS; but you shouldn't be doing this anyway.
    
    There's a fourth aspect of mail delivery privilege which is creation of
    the user's mailbox. The MTA or its helper programs need to be able to
    create the mbox if it isn't there; and may you also have to accomdate
    people putting procmail in their .forward files.
    
    So far, the .maildir concept is the best approach I've seen to solve
    the issues surrounding delivery to the user's mailbox because it is the
    only one AFAICT where you only cross privilege boundaries "downward"
    i.e. from a system service to a user service, and never the other way
    round (e.g. setgid mail helpers for creating lock files).
    
    Olaf
    -- 
    Olaf Kirch         |  --- o --- Nous sommes du soleil we love when we play
    okirat_private  |    / | \   sol.dhoop.naytheet.ah kin.ir.samse.qurax
    okirat_private    +-------------------- Why Not?! -----------------------
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