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Re: Symlink problem (Tested only on a Digital Unix 4.0)
From: jmcdonal () UNF EDU (John McDonald)
Date: Tue, 7 Apr 1998 13:09:55 -0400


It seems also that if you do not have read privileges on a program that
you execute, it will not core dump. So another quick fix to this problem
would be to take read permissions away on all your suids.

humble

On Tue, 7 Apr 1998, Paul Szabo wrote:

(Aleph1 and rusty: please ignore my previous, similar message...)

rusty () mad it wrote:
Symlink problem in Digital Unix 4.0 ...
Starting 2 suid root programs ... and killing them with -11 flag ...
$ ln -s /.rhosts core
$ ping somehost &
[1] 1337
$ ping somehost &
[2] 31337
$ kill -11 31337
$ kill -11 1337
[1]    Segmentation fault   /usr/sbin/ping somehost (core dumped)
[2]    +Segmentation fault   /usr/sbin/ping somehost (core dumped)
$ ls -l /.rhosts
-rw-------   1 root     system    385024 Mar 29 05:17 /.rhosts

Other platforms:

SunOs    4.1.x 5.5.x    Doesn't work
Linux       2.0.x             Doesn't work
Digital Unix 4.0d         Doesn't work
Others     (note tested yet)

I can reproduce this on Digital Unix 4.0B (OSF1 V4.0 564), with just one
setuid program:

% unsetenv DISPLAY; xterm

The only defence I can offer is to put the following line into the file
/sbin/rc3 (this is a sh script; most processes run by users are descendants
of this):

ulimit -h -c 0

However this does not work for processes started from /etc/inittab: getty
(console and tty) logins. Instead of modifying /sbin/rc3, you could try
changing /etc/inittab to read something like:

s3:3:wait:sh -c 'ulimit -h -c 0; /sbin/rc3 < /dev/console > /dev/console 2>&1'
cons:1234:respawn:sh -c 'ulimit -h -c 0; /usr/sbin/getty console console vt100'

Obviously this prevents creating core files in all cases; fortunately our
users never need them to debug their own programs.

Paul Szabo - System Manager   //        School of Mathematics and Statistics
psz () maths usyd edu au         //   University of Sydney, NSW 2006, Australia




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