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Re: vixie cron possible local root compromise
From: "Settle, Sean" <SeanSettle () ALLIANTFS COM>
Date: Wed, 14 Feb 2001 17:42:36 -0700

% uname -smr; man passwd
FreeBSD 4.2-RELEASE i386
             Login name.  May contain only lowercase characters or digits.
             Maximum length is 16 characters (see setlogin(2) BUGS section).
             The reasons for this limit are "Historical".  Given that people
             have traditionally wanted to break this limit for aesthetic
             sons, it's never been of great importance to break such a basic
             fundamental parameter in UNIX.  You can change UT_NAMESIZE in
             /usr/include/utmp.h and recompile the world; people have done
             this and it works, but you will have problems with any precom-
             piled programs, or source that assumes the 8-character name
             and NIS.  The NIS protocol mandates an 8-character username.
             you need a longer login name for e-mail addresses, you can
             an alias in /etc/mail/aliases.

On HP-UX I couldn't find this information in passwd or useradd.  I took a
peek at 'man utmp' and found this, but it's probably not the final word on
the subject:

              struct    utmp {
                char   ut_user[8];           /* User login name */
                char   ut_id[4];             /* /etc/inittab id(usually
                char   ut_line[12]           /* device name (console, lnxx)
                pid_t  ut_pid;               /* process id */

Sean Settle
"To sin by silence when we should protest makes cowards out of men" - Ella
Wheeler Wilcox
X Network Services Q NPC X
Phoenix, AZ
SMTP:   seansettle () alliantfs com

-----Original Message-----
From: Valdis Kletnieks [mailto:Valdis.Kletnieks () VT EDU]
Sent: Wednesday, February 14, 2001 9:34 AM
Subject: Re: vixie cron possible local root compromise

On Tue, 13 Feb 2001 22:27:14 -0200, "Rodrigo Barbosa (aka morcego)"
<rodrigob () CONECTIVA COM BR>  said:

#include <wtmpx.h>

main () {

Of course, what's important isn't what wtmpx.h defines it as, but what pwd.h
has to say about it.  If getpwent() won't handle it, your wtmp format

Note also that some systems have utmpx.h not wtmpx.h

If anyone can find any system that reports less then 32, it will be an
of the rule. Of course I mean current systems. libc5 systems, AIX 3.2 and
systems like that will probably return 16 or even 8.

AIX 4.3.3 and AIX 5.0 both limit it to 8 in utmpx.h

Solaris 5.7 has a 32-char limit in wtmp, but has this in 'man useradd':

     The login field  (login ) is a string  no  more  than  eight
     bytes  consisting  of  characters from the set of alphabetic
     characters,  numeric  characters,  period   (.),  underscore
     (_),  and  hypen   (-). The first character should be alpha-
     betic and the field should contain at least one  lower  case
     alphabetic  character.  A warning message will be written if
     these restrictions are not met. A future Solaris release may
     refuse  to  accept  login  fields  that  do  not  meet these
     requirements. The login field  must  contain  at  least  one
     character  and  must  not  contain a colon  (:) or a newline

SGI 6.5.10f has a 32-char limit in utmpx.h, but 'man 4 passwd' says this:

     name      User's login name -- consists of alphanumeric characters and
               must not be greater than eight characters long.  It is
               recommended that the login name consist of a leading lower
               letter followed by a combination of digits and lower case
               letters for greatest portability across multiple versions of
               the UNIX operating system.  This recommendation can be safely
               ignored for users local to IRIX systems.  The pwck(1M)
               checks for the greatest possible portability on names, and
               complains about user names that do not cause problems on

I'll let somebody else check Tru64 and HP/UX, I don't have access to them
at the moment.

Moral of the story:  Not all the world is Linux, and some vendors care
more about backward and cross compatability than being the

                                Valdis Kletnieks
                                Operating Systems Analyst
                                Virginia Tech

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