Date: Fri, 30 Apr 1999 10:05:33 -0700 From: Cy Schubert <cschuber@uumail.gov.bc.ca> To: "Pedro J. Lobo" <pjlobo@euitt.upm.es> Cc: freebsd-security@FreeBSD.ORG Subject: Re: Does mail.local need to be setuid-root? Message-ID: <199904301706.KAA00762@passer.osg.gov.bc.ca> In-Reply-To: Your message of "Fri, 30 Apr 1999 15:47:18 %2B0200." <Pine.OSF.4.05.9904301535330.15810-100000@haddock.euitt.upm.es>
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In message <Pine.OSF.4.05.9904301535330.15810-100000@haddock.euitt.u
pm.es>, "Pe
dro J. Lobo" writes:
> Hello, people.
>
> I have a 3.1-RELEASE machine which, among other tasks, acts as a mail and
> telnet server for out students. Recently I noticed that several users were
> using more disk space than his quotas should allow (!). After a bit of
> investigation, I have traced down the problem to the mail system.
>
> The problem is that you cand send mail to a user that is over quota, and
> the system will append the new message to its inbox (located in /var/mail,
> as by default). Indeed, root can append data to a file that belongs to a
> user that is over quota.
>
> As you may see, it is a rather ugly "feature". So, the question is: does
> /usr/libexec/mail.local need to be setuid root? Or, alternatively, can I
> use /usr/bin/mail as the local mailer? I also administer an alpha with
> Tru64 Unix 4.0d and it uses /bin/mail (no setuid/setgid) as the local
> mailer.
The main difference between DU and FreeBSD is:
DU 4.0D:
OSF1 hostname V4.0 878 alpha
drwxrwxrwt 2 root mail 512 Apr 26 00:00
/var/spool/mail
lrwxrwxrwx 1 root system 7 Dec 9 14:16 /bin ->
usr/bin
-rws--x--x 2 root bin 40960 Dec 29 1997 /usr/bin/mail
FreeBSD 3.1R:
FreeBSD hostname 3.1-RELEASE FreeBSD 3.1-RELEASE #0: Thu Apr 8
16:05:54 PDT 1999 root@hostname:/opt/usr_src-310/sys/compile/HOS
TNAME i386
drwxrwxr-x 2 root mail 512 Apr 30 09:41 /var/mail
-r-sr-xr-x 1 root wheel 15056 Mar 2 06:53 /usr/libexec/mail.loca
l
Solaris 2.6 (for good measure):
SunOS HOSTNAME 5.6 Generic_105181-12 sun4u sparc SUNW,Ultra-Enterpri
se
drwxrwxrwt 3 root mail 512 Apr 29 23:45 /var/mail
-r-x--s--x 1 bin mail 64376 Jul 15 1997 /bin/mail
You can resolve your issue by making mail.local sgid mail instead
of suid root. Ownership of individual mail files cannot be set by
mail.local when its sgid mail, so you will need to create each
individual user's mail spool file with the proper permissions 660
and ownership before they can receive mail. If mail.local is the
only sgid mail application on your system, using sgid mail
shouldn't be any less secure (from a privacy point of view) than
the stock-out-of-the-box setup.
Regards, Phone: (250)387-8437
Cy Schubert Fax: (250)387-5766
Open Systems Group Internet: Cy.Schubert@uumail.gov.bc.ca
ITSD Cy.Schubert@gems8.gov.bc.ca
Province of BC
"e**(i*pi)+1=0"
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