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From: Malcolm Kay <malcolm.kay@internode.on.net>
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To: Barbish3@adelphia.net, "MICSKO Viktor" <candiru@bazmag.hu>
Date: Sun, 27 Jun 2004 16:14:06 +0930
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Subject: Re: setting a disk read only
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On Saturday 26 June 2004 22:06, JJB wrote:
> Security Paranoia
> It's very important that you completely understand the impact of
> using the following command will have on your ability to make
> changes to your system.
>
> The simplest thing you can do is set the immutable flag on all
> system binaries and /etc config files with:
>
> chflags schg /bin/*(*) /sbin/*(*) /usr/bin/*(*) /usr/sbin/*(*)
> /etc/*(*)
>
It seems to me that mounting all partitions from the disk as read only
would achieve rather more; and more simply.

But neither protects against direct writes to the raw device. 
And if you are really paranoid about this I think the only solution is a 
hardware switch. I suspect the linux 'hdparm' also has its limitations;
only a hardware switch can protect against software bugs or a successful
invasion.

> Setting the immutable flag on, means the files are marked as being
> protected from being written over. Once you execute the above
> command, no process can over write those files thus increasing the
> level of difficulty for the attacker and increasing the odds in your
> favor of the attacker leaving error messages in the system log. On
> the other hand you as root user can not make any changes to those
> file so marked either.
>
> Ever time you want to make changes you have to issue the command to
> turn off the immutable flag on all the same files. Use this command
> to do that:
>
> chflags noschg /bin/*(*) /sbin/*(*) /usr/bin/*(*) /usr/sbin/*(*)
> /etc/*(*)
>
> You can use "ls -lo" command to see the immutable flags of existing
>
> You could do this to any slice with chflags noschg /*(*)  /usr/*(*)
> what ever
>

Malcolm