keyboard & screen security

keyboard & screen security

Post by Casper H.S. D » Wed, 09 Feb 1994 17:28:44

> OT> I can mess up host1's display and lock its keyboard. And someone else
> OT> can do the same thing to me when I was logged in to host1 from
> OT> console.
> OT> Is there a way to prevent this ? or at least detect who did this ?
>Use /etc/fbtab; it's yet another thing Sun ships turned off by default
>(like their brains, I can't help thinking).

One pleasant surprise in Solaris 2.3, where it's turned on
by default.  The file is called ``/etc/logindevperm''

The default in Solaris 2.3 looks like:

/dev/console    0600    /dev/mouse:/dev/kbd
/dev/console    0600    /dev/sound/*            # audio devices
/dev/console    0600    /dev/fbs/*              # frame buffers



keyboard & screen security

Post by Alan Pee » Thu, 10 Feb 1994 08:00:56

>>   Use /etc/fbtab; it's yet another thing Sun ships turned off by default
>>   (like their brains, I can't help thinking).

>>   # Description:
>>   # If the user is logging in on a device specified in the "console" field
>>   # of any entry in this file, the owner/group of the devices listed in the
>>   # "device_list" field will be set to that of the user.  Similarly, the mode
>>   # will be set to the mode specified in the "mode" field.

>>   --

>>     "It's 106 ms to Chicago, we've got a full disk of GIFs, half a meg of
>>        hypertext, it's dark, and we're wearing sunglasses."  "Click it."

If you are using XDM logins you might want to verify the behavior of
fbtab on your systems.  Since the X11R5 XDM does not seem to know
about this, we manage these devices by hand in the Xsession script.

I don't know about OpenWindows.


Alan Peery
Institute for Scientific Computation
Texas A&M University


1. chroot && mount -o bind && security

Is there a way to mount an already mounted filesystem using the
bind mount procedure by referencing the filesystem using a device?

Here's my idea:

Linux boots up with hda1 mounted as / and runs a custom init.
Some processes may be started at this point, or maybe not.
A 2nd filesystem, hda2, will be mounted at (the arbitrarily
chosen path of) /sys.  The 2nd filesystem (with whatever else
gets mounted within there) is a complete run-time system.
The modified init will read /sys/etc/inittab and for every
process started according to that inittab, it will chroot()
the child to /sys before execve()-ing the specified program.
With /sys/etc/inittab being the startup for a complete system,
that system will really be running in the chroot context.
What few processes run in the original root context would be
restricted to doing things more securely, such as not running
servers which might be exploitable (this might mean running
nothing at all).

The question is whether, if a root process running in the hda2
context is exploited and totally controlled, can it then mount
hda1 some way to bypass the chroot barrier?

What I've tried so far suggests the answer might be "no".  But
I cannot be sure I have tried everything (a common problem in
security analysis).  So I'm hoping someone who has a better
understanding of how bound mount works (or at least is supposed
to work) might have some insight into this.

I've also considered using pivot_root(), but that ends up with
the original root being a subdirectory of the new root, and is
thus not really secure.  I could then unmount the original root,
but then it can be mounted again by having a device node for
the original filesystem.  So I think chroot() while keeping the
original root mounted (to prevent further mounting as long as
bind mount doesn't leak this) might make this more secure.

Of course it might be possible to write on the device itself.
But I think this can be more easily addressed.

| Phil Howard - KA9WGN |   Dallas   | |


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