How to Limit Display of Other User's Processes

This entry is a continuation of my list of lesser known and/or publicized security enhancements to the Solaris 10 OS. In this update, I will be talking about how to restrict the output of the ps(1) command such that users can only see processes that they own. This is a very useful capability especially for ISPs and other organizations that do not want to allow users to see what other users are doing.

This new feature would not have been possible without the introduction of process privileges into the Solaris 10 OS. For a great overview of process privileges, see Casper Dik's blog entry on this topic. Be sure to read his article to get a more in depth understanding of process privileges.

So, before we begin, let's see what the output of ps -aef might look like for an average user (in this case, gmb):

$ ps -aef
     UID   PID  PPID   C    STIME TTY         TIME CMD
    root     0     0   0   Sep 23 ?           0:07 sched
    root     1     0   0   Sep 23 ?           0:01 /sbin/init
    root     2     0   0   Sep 23 ?           0:00 pageout
    root     3     0   0   Sep 23 ?           2:31 fsflush
    root   393     1   0   Sep 23 ?           0:00 /usr/sbin/auditd
    root     7     1   0   Sep 23 ?           0:11 /lib/svc/bin/svc.startd
    root     9     1   0   Sep 23 ?           0:19 svc.configd
    root   176     1   0   Sep 23 ?           0:00 /usr/sbin/syslogd
    root    64     1   0   Sep 23 ?           0:00 /usr/sbin/nscd
  daemon    91     1   0   Sep 23 ?           0:02 kcfd
    root   170     1   0   Sep 23 ?           0:01 /usr/lib/utmpd
     gmb  1795  1792   0 22:17:26 pts/1       0:00 -sh
    root  1527     7   0 00:53:24 console     0:00 /usr/bin/login
    root    82     1   0   Sep 23 ?           0:00 /usr/lib/sysevent/syseventd
   smmsp   334     1   0   Sep 23 ?           0:00 /usr/lib/sendmail -Ac -q15m
  daemon   137     1   0   Sep 23 ?           0:06 /usr/sbin/rpcbind
    root    84     1   0   Sep 23 ?           0:00 /usr/lib/picl/picld
    root  1601  1527   0 07:36:19 console     0:00 -sh
    root   181     1   0   Sep 23 ?           0:04 /usr/lib/inet/inetd start
    root   281     1   0   Sep 23 ?           0:00 /usr/lib/nfs/mountd
    root   187     1   0   Sep 23 ?           0:00 /usr/sbin/cron
    root  1402     1   0 00:26:14 ?           0:00 /usr/lib/ssh/sshd
  daemon   289     1   0   Sep 23 ?           0:00 /usr/lib/nfs/nfsd
  daemon   264     1   0   Sep 23 ?           0:00 /usr/lib/nfs/statd
    root   303     1   0   Sep 23 ?           0:00 /usr/lib/fm/fmd/fmd
  daemon   268     1   0   Sep 23 ?           0:00 /usr/lib/nfs/lockd
    root   291     1   0   Sep 23 ?           0:00 /usr/lib/autofs/automountd
     gmb  1799  1795   0 22:17:28 pts/1       0:00 ps -aef
    root  1789   181   1 22:17:19 ?           0:00 /usr/sbin/in.telnetd
    root  1792  1789   1 22:17:19 pts/1       0:00 login -p -h 10.1.1.100 -d /dev/pts/1
    root   335     1   0   Sep 23 ?           0:06 /usr/lib/sendmail -bd -q15m
  daemon   296     1   0   Sep 23 ?           0:00 /usr/lib/nfs/nfsmapid

As you can see, the gmb user can see not only his processes but also those of the root, daemon, and smmsp accounts. We can change this behavior either globally or on a per-user basis. Just as we discussed in the Solaris 10 Account Lockout entry, we can use user-specific changes to force a subset of users to comply with some policy or use the user-specific changes to make exceptions for those users. The flexibility of this format allows it to be adapted quite easily to the needs of many organizations.

For our first example, we will illustrate how the global change can be made. So do this, we must edit the /etc/security/policy.conf file, uncomment the PRIV_DEFAULT entry and set its value as follows:

PRIV_DEFAULT=basic,!proc_info

For those not familiar with the proc_info privilege, you can find more information about it using the ppriv(1) command:

# ppriv -l -v proc_info
proc_info
        Allows a process to examine the status of processes other
        than those it can send signals to.  Processes which cannot
        be examined cannot be seen in /proc and appear not to exist.

This is all that you need to do to globally configure your Solaris 10 system so that users will only be able to see processes that they own. Note that this will obviously not apply to root who by default has all privileges or to other users or processes that have been explicitly given the proc_info privilege. Regardless, it is still a very quick and effective way to limit what processes users may see.

Returning to the gmb account example, I re-login to the system and again run the ps -aef command, but this time I receive different results:

$  ssh -l gmb sampleHost
gmb@sampleHost's password:
Last login: Fri Sep 24 22:25:18 2004 from 10.1.1.100
Sun Microsystems Inc.   SunOS 5.10      s10_67  May 2004
$ ps -aef
     UID   PID  PPID   C    STIME TTY         TIME CMD
     gmb  1823  1819   0 22:30:17 pts/1       0:00 ps -aef
     gmb  1819  1815   0 22:30:14 pts/1       0:00 -sh
$

As you can see, the gmb user may now only see his own processes. Way cool. Next, to illustrate the per-user configuration ability, I will leave this global configuration in place and use the per-user configuration ability to allow the gmb user to view processes owned by other users. This is just an example of how exceptions can be implemented. The same process could be used to enable this feature for just a user or subset of users on the system.

To accomplish this task, we go back to the user_attr(4) file. In this file, we will modify the existing entry for the gmb user (or create one if one had not already been there). The following example illustrates the change that needs to be made. Specifically you need to add the defaultpriv entry to specify the default list of privileges that will be available to this user. By modifying this parameter, you will change the default set of privileges available to a user (by either adding or removing privileges as needed.) In this case, we are returning the user's default set of privileges to basic from basic,!proc_info.

gmb::::lock_after_retries=no;defaultpriv=basic

So, let's see if this really works. In the following example, we will confirm the configuration of the system, login to the system as the gmb user, and run the ps -aef command to verify that the gmb user can see processes owned by other users.

# grep "\^PRIV_DEFAULT=" /etc/security/policy.conf
PRIV_DEFAULT=basic,!proc_info
# grep "\^gmb:" /etc/user_attr
gmb::::lock_after_retries=no;defaultpriv=basic
# ssh -l gmb localhost
Password:
Last login: Fri Sep 24 22:37:55 2004 from 10.1.1.100
Sun Microsystems Inc.   SunOS 5.10      s10_67  May 2004
$ id -a
uid=100(gmb) gid=1(other) groups=1(other)
$ ps -aef
     UID   PID  PPID   C    STIME TTY         TIME CMD
    root     0     0   0   Sep 23 ?           0:07 sched
    root     1     0   0   Sep 23 ?           0:01 /sbin/init
    root     2     0   0   Sep 23 ?           0:00 pageout
    root     3     0   0   Sep 23 ?           2:33 fsflush
    root   393     1   0   Sep 23 ?           0:00 /usr/sbin/auditd
    root     7     1   0   Sep 23 ?           0:11 /lib/svc/bin/svc.startd
    root     9     1   0   Sep 23 ?           0:19 svc.configd
    root   176     1   0   Sep 23 ?           0:00 /usr/sbin/syslogd
    root    64     1   0   Sep 23 ?           0:00 /usr/sbin/nscd
  daemon    91     1   0   Sep 23 ?           0:02 kcfd
    root   170     1   0   Sep 23 ?           0:01 /usr/lib/utmpd
    root  1900  1402   7 22:42:05 ?           0:02 /usr/lib/ssh/sshd
    root  1527     7   0 00:53:24 console     0:00 /usr/bin/login
    root    82     1   0   Sep 23 ?           0:00 /usr/lib/sysevent/syseventd
   smmsp   334     1   0   Sep 23 ?           0:00 /usr/lib/sendmail -Ac -q15m
  daemon   137     1   0   Sep 23 ?           0:06 /usr/sbin/rpcbind
    root    84     1   0   Sep 23 ?           0:00 /usr/lib/picl/picld
    root  1601  1527   0 07:36:19 console     0:00 -sh
    root   181     1   0   Sep 23 ?           0:04 /usr/lib/inet/inetd start
    root   281     1   0   Sep 23 ?           0:00 /usr/lib/nfs/mountd
    root   187     1   0   Sep 23 ?           0:00 /usr/sbin/cron
    root  1402     1   0 00:26:14 ?           0:00 /usr/lib/ssh/sshd
  daemon   289     1   0   Sep 23 ?           0:00 /usr/lib/nfs/nfsd
  daemon   264     1   0   Sep 23 ?           0:00 /usr/lib/nfs/statd
    root   303     1   0   Sep 23 ?           0:00 /usr/lib/fm/fmd/fmd
  daemon   268     1   0   Sep 23 ?           0:00 /usr/lib/nfs/lockd
    root   291     1   0   Sep 23 ?           0:00 /usr/lib/autofs/automountd
     gmb  1912  1908   0 22:42:12 pts/1       0:00 ps -aef
    root   335     1   0   Sep 23 ?           0:06 /usr/lib/sendmail -bd -q15m
  daemon   296     1   0   Sep 23 ?           0:00 /usr/lib/nfs/nfsmapid
     gmb  1908  1900   0 22:42:10 pts/1       0:00 -sh
    root  1899  1601   6 22:42:05 console     0:02 ssh -l gmb localhost

It worked! That was pretty easy, right? This is just one very small example of how you can use process privileges in your daily lives. I will try to add more interesting examples of practical uses for process privileges in the future.

Before ending, I do want to highlight that while these examples focused on the ps(1) command - other process related commands will also be impacted such as ptree(1), pcred(1), pmap(1), psig(1), etc. Further, as a user running without the proc_info privilege, you will not even be able to see other processes in the /proc directory:

$ id -a
uid=101(foo) gid=1(other) groups=1(other)
$ ppriv $$
1915:   -sh
flags = 
        E: basic,!proc_info
        I: basic,!proc_info
        P: basic,!proc_info
        L: all
$ ls -l /proc
total 4
dr-x--x--x   5 foo      other        832 Sep 24 22:52 1915
dr-x--x--x   5 foo      other        832 Sep 24 22:56 1932

I hope you enjoyed this article and please watch this space for new discussion of Solaris 10 security features. Take care and have a great weekend.

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Comments:

Thank you for that. It is very informative and will be useful for my purposes.

Posted by PatrickG on September 24, 2004 at 06:13 PM EDT #

Real useful entry. The whole blog is very interesting.

Posted by Vlad Grama on September 24, 2004 at 10:38 PM EDT #

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