Linux: Hide Processes From Other Users

Written by BiRU Sunday, 09 April 2017 08:30

Attention: open in a new window. PDFPrintE-mail

 

I run a multi-user system. Most users access resources using ssh client. How can I stop leaking process information to all users on Linux operating systems? How do I prevent users from seeing processes that do not belong to them on a Debian/Ubuntu/RHEL/CentOS Linux server?

If you are using Linux kernel version 3.2+ (or RHEL/CentOS v6.5+ above) you can hide process from other users. Only root can see all process and user only see their own process. All you have to do is remount the /proc filesystem with the Linux kernel hardening hidepid option.

Say hello to hidepid option

This option defines how much info about processes we want to be available for non-owners. The values are as follows:

  1. hidepid=0 – The old behavior – anybody may read all world-readable /proc/PID/* files (default).
  2. hidepid=1 – It means users may not access any /proc// directories, but their own. Sensitive files like cmdline, sched*, status are now protected against other users.
  3. hidepid=2 It means hidepid=1 plus all /proc/PID/ will be invisible to other users. It compicates intruder’s task of gathering info about running processes, whether some daemon runs with elevated privileges, whether another user runs some sensitive program, whether other users run any program at all, etc.

Linux kernel protection: Hiding processes from other users

Type the following mount command:
# mount -o remount,rw,hidepid=2 /proc
Edit /etc/fstab, enter:
# vi /etc/fstab
Update/append/modify proc entry as follows so that protection get enabled automatically at server boot-time:

proc    /proc    proc    defaults,hidepid=2     0     0

Save and close the file.

Linux demo: Prevent users from seeing processes that do not belong to them

In this example, I’m login as vivek@cbz-test:
$ ssh vivek@cbz-test
$ ps -ef
$ sudo -s
# mount -o remount,rw,hidepid=2 /proc
$ ps -ef
$ top
$ htop
Sample outputs:

Animated gif 01: hidepid in action

Animated gif 01: hidepid in action

Tip: Dealing with apps that breaks when you implement this technique

You need to use gid=VALUE_HERE option:

gid=XXX defines a group that will be able to gather all processes’ info (as in hidepid=0 mode). This group should be used instead of putting nonroot user in sudoers file or something. However, untrusted users (like daemons, etc.) which are not supposed to monitor the tasks in the whole system should not be added to the group.

So add the user called monapp to group (say admin) that want to see process information and mount /proc as follows in /etc/fstab:

proc /proc proc defaults,hidepid=2,gid=admin 0 0