linux-kernel - Re: [PATCH RFC] tpm: define a command filter

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Message-ID: <20170124143600.siyhblj67qaatewi@intel.com>
Date:   Tue, 24 Jan 2017 16:36:00 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     tpmdd-devel@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] tpm: define a command filter

On Mon, Jan 23, 2017 at 05:19:18PM -0700, Jason Gunthorpe wrote:
> On Tue, Jan 24, 2017 at 02:02:52AM +0200, Jarkko Sakkinen wrote:
> > This commit adds a command filter for whitelisting a set of commands in
> > a TPM space. When a TPM space is created through /dev/tpms0, no
> > commands are allowed. The user of the TPM space must explicitly define
> > the list of commands allowed before sending any commands. This ioctl is
> > a one shot call so that a resource manager daemon can call it before
> > sending the file descriptor to the client.
> 
> I don't think it makes sense to have a daemon in user space that
> passes an open'd /dev/tpms0 FD directly to a client..
> 
> It is trivial and more powerful to just proxy the messages. Can you
> see some reason why passing a FD through a daemon would make sense?
> 
> The earlier discussion with James was to have some way to apply a
> global command filter to all tpms0 users with the idea that the
> 'right' restricted command set would enable a 0666 cdev node, and no
> daemon.

Is that a conflicting goal?

Maybe the ioctl could be restricted by CAP_MAC_ADMIN in that case?

How would you propose to change the code below? I guess the "core
code" is about right and this is more about API, am I right?

/Jarkko

> 
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > 1. This patch applies on top of 'tabrm4' brach.
> > 2. Only compilation is tested (just drafted the idea)
> >  drivers/char/tpm/tpm-interface.c | 12 +++++--
> >  drivers/char/tpm/tpm.h           |  1 +
> >  drivers/char/tpm/tpm2-space.c    |  7 ++++
> >  drivers/char/tpm/tpms-dev.c      | 75 ++++++++++++++++++++++++++++++++++++++++
> >  include/uapi/linux/tpms.h        | 29 ++++++++++++++++
> 
> BTW, don't forget to update kbuild when you add uapi files... Applies
> to other patches..
> 
> Jason