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Re: Malicious devices & vulnerabilties
From: Alistair Crooks <agc () netbsd org>
Date: Sun, 8 Jan 2012 22:18:07 +0100

On Mon, Jan 09, 2012 at 03:48:20AM +0800, Eugene Teo wrote:
On 01/08/2012 07:19 PM, Florian Weimer wrote:
* Xi Wang:

I am wondering where to draw the line.  Should such device drivers
be considered vulnerable or not?  Thanks.

I think they should be considered vulnerable.  Some applications need
some robustness to attacks even from the local console (e.g., student
computer rooms).

USB is also a popular transport in many air-gapped environments.

I would consider them vulnerable with low security impacts. If you are
fixing such issues, do post them to the list.

One very interesting datapoint here is Antti Kantee's rump subsystem
in NetBSD

        http://www.netbsd.org/docs/rump/
        http://blog.netbsd.org/tnf/entry/runnable_userspace_meta_programs_in

which allows for userspace-mounting of devices and filesystems
thereon.  Unknown provenance USB sticks are one of the use cases
mentioned.

        + rump_msdos:  USB sticks with FAT file systems are a common
        sight.  Mounting an untrusted image from removable media with
        the file system driver running in the kernel is risky in many
        ways:  inopportune unplugging of the media or a corrupted file
        system may have adverse effects such as system crashes or
        worse.  By using the rump_msdos command instead of
        mount_msdos, the file system service runs in userspace and is
        accessed via puffs.  This isolates the main kernel from any
        resulting problems such as buffer overflows.

        The usage of mount_msdos and rump_msdos are equivalent...

If USB is a transport in air-gapped environments, I personally have a
concern with that. A good thing airgaps aren't used for anything in RL,
right? ;-)

Regards,
Alistair

PS. Obvious disclaimer - I am biased.
PPS. Just reading REAMDE right now
--
Alistair Crooks
{agc,security-officer} () NetBSD org


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