CentOS - Dec 2008 - Information about ASLR (Address Space Layout Randomization) in CentOS 5

Hi,

We are porting some applications from CentOS 4 to CentOS 5, the
applications use mmap, and we found out that they sometimes crash in
CentOS 5. We found out that this is due to the fact that CentOS 5 does
randomization of the address space when loading binaries, libraries,
and when using mmap, so that is what's causing our problem.

The thing is, I'm trying to google for it, but I did not find any
useful information on ASLR present in CentOS 5/RHEL 5/Linux 2.6.18. If
anyone has any good pointers on reliable information on what does that
code do, how to configure/tweak it, or how to use mmap properly to
work around the issues, I would really appreciate it. In particular,
if there is a switch/option that would allow us to disable it for some
binaries/libraries only, it would be great, since this could allow us
to do the upgrade sooner and try to find the proper fix for the
problem later.

Thanks!
Filipe

In article <e814db780812120659qd384182y8f8c1a69d39c2e2e at
mail.gmail.com>,
Filipe Brandenburger <filbranden at gmail.com>
wrote:
> Hi,
> 
> We are porting some applications from CentOS 4 to CentOS 5, the
> applications use mmap, and we found out that they sometimes crash in
> CentOS 5. We found out that this is due to the fact that CentOS 5 does
> randomization of the address space when loading binaries, libraries,
> and when using mmap, so that is what's causing our problem.
> 
> The thing is, I'm trying to google for it, but I did not find any
> useful information on ASLR present in CentOS 5/RHEL 5/Linux 2.6.18. If
> anyone has any good pointers on reliable information on what does that
> code do, how to configure/tweak it, or how to use mmap properly to
> work around the issues, I would really appreciate it. In particular,
> if there is a switch/option that would allow us to disable it for some
> binaries/libraries only, it would be great, since this could allow us
> to do the upgrade sooner and try to find the proper fix for the
> problem later.
>From what I've been able to find, you can disable ASLR completely by
putting the following line in /etc/sysctl.conf:

kernel.randomize_va_space = 0

Alternatively, you can run your program with ASLR disabled by using
setarch to invoke it:

setarch `uname -m` -R yourprog <yourprogoptions>

The -R option disables randomisation.  You might want to look at
the -L option for setarch too (man setarch).

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org