[refpolicy] labels on /dev/tty.*

Jason Zaman jason at perfinion.com
Sun Oct 26 04:41:03 UTC 2014


On Thu, Oct 23, 2014 at 08:14:56AM -0400, Christopher J. PeBenito wrote:
> On 10/22/2014 12:09 PM, Jason Zaman wrote:
> > Hi all,
> > 
> > I am confused about the labels on the tty dev nodes. I looked in refpol
> > and the only fcontext is:
> > 
> > /dev/.*tty[^/]* -c gen_context(system_u:object_r:tty_device_t,s0)
> > 
> > The implications of this are that everything is labelled with
> > tty_device_t but I am pretty sure this is wrong. I have seen several
> > different types of nodes which I think should have separate labels.
> > 
> > Ones that I am aware of (please add more or correct my understanding if
> > it is wrong)
> > 
> > /dev/tty0 -- The consoles (eg ctrl+alt+f1)
> > /dev/ttyS -- A physical serial port
> > /dev/ttyUSB0 -- A usb-to-serial port
> > /dev/ttyACM0 -- I have seen this for both usb-to-serial on embedded
> > microcontrollers as well as 3G modems and the like.
> > /dev/usb/tty.* -- I have no idea what this is, its not on my system but
> > it is labelled usbtty_device_t in refpol.
> > 
> > The label on tty0 seems correct, the label on ttyUSB0 and ttyACM0 should
> > probably be usbtty_device_t. As for what the label should be on ttyS0, I
> > am not sure.
> > 
> > Thoughts? I dont want to just send in a patch changing this before I
> > understand *exactly* what these are used for in case they break
> > something else.
> 
> It seems more likely that usbtty_device_t should be dropped.  I don't
> see any reason for there to be a distinction based on the underlying
> hardware.
> 
I was hoping more like having one label for /dev/tty0 (ie the consoles) and
a different label for the rest (ie ttyS0, ttyACM0, ttyUSB0). In my case, I want my
normal user to be able to access the usb-to-serial device but I see no
reason why my user should have access to all the consoles.

Dominick said fedora has something like modem_device_t for ttyACM0 which
makes sense. Perhaps a more generic serial_device_t is better to use for
all of them instead?

> 
> -- 
> Chris PeBenito
> Tresys Technology, LLC
> www.tresys.com | oss.tresys.com


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