Re: [HPLIP-Devel] HP Linux Imaging and Printing System (HPLIP) 2.7.10 Release

[Suffield, D. <dav...@hp...>]

Hi Johannes,=20

> As far as I understand it, traditional security in Unix/Linux=20
> (i.e. without additional stuff like AppArmor or SELinux) is=20
> done by a separation by using different user accounts.
>=20
> Here changing the device file permissions is separated from=20
> using the device file (under the given permissions) by using=20
> different user accounts for the device file owner (the only=20
> user account - except "root" - which can change the=20
> permissions) and for those who should only use it.
>=20
> Therefore OWNER=3D"johndoe", GROUP=3D"lp", MODE=3D"0666"
> would also do this separation (now only "johndoe" and "root"
> can change the permissions) but usually it is not desired=20
> that "johndoe" can change device file permissions so that I=20
> simply use the "default system owner" which is "root".

Good analogy - device file permissions for ownership is separate from
device file permissions for using the device file (ie: group and other).
Only the device owner has the right to change device file permissions.

I plan on changing the OWNER=3D"lp" to OWNER=3D"root" in the =
55-hpmud.rules
file.

> > > For MODE=3D"0666" the crucial question is whether or not it is=20
> > > possible that another user (e.g. someone who is logged in from=20
> > > remote) can somehow eavesdrop when a (confidental) document is=20
> > > printed or scanned.
> > >=20
> > > Is eavesdropping somehow possible with MODE=3D"0666"?
> >=20
> > Given only one process can claim the USB interface for reading or=20
> > writing, and claiming the interface is arbitrated by the kernel, I=20
> > would say no other process could snoop the print job or scan job.
>=20
> Could you give me some more details what hpmud does to open=20
> the device file so that I can let our security team have a=20
> look at it or should they simply check all the files in io/hpmud/?

Yes, all the hplip i/o code is in io/hpmud.

For usb all i/o goes through libusb/usbfs. All read/writes to any
end-point require a claim_usb_interface(). Once the interface is claimed
all i/o to that interface is exclusive (ie: 7/1/2).

Parallel i/o is similar. All hpmud parallel i/o goes through
ppdev/parport. Before any i/o can take place PPCLAIM will claim
exclusive access to the port (ie: /dev/parport0).=20

-dave=20