Re: Udev hardening

[Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>]

On Mon, Dec 14, 2020 at 05:31:17PM +0200, Adi Ml wrote:
> I am using udev in order to create a kiosk mode. I want to block devices
> which fit a certain vid pid.

Block devices from where?  The kernel or userspace?

udev runs _after_ the kernel has seen the device and bound to it.

And usb vid/pids can be made to be whatever they want to be, be careful
about triggering off of them to prevent specific things from happening,
that way is tough.  It's easier to whitelist valid devices that you know
are correct, and then only allow specific actions to happen on them.

You might want to look into using https://usbguard.github.io/ for how to
do this "properly".

> I want to filter system calls anyway because I
> dont know which devices are entered and I want to avoid devices which will
> do unusual things like rubber ducky.

devices do not make system calls directly, and if you plug a rubber
ducky in that acts like a keyboard, that is not going to create things
in udev's process context.

> What do you mean by filtering system calls in   scripts- is it needed when
> the user can influence actions commited in the script ?

Look at the programs / scripts that udev calls out to in the udev
configuration files for examples of these.  A user does not directly
influence them, except if they are allowed to create/remove hardware.

Hope this helps,

greg k-h
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