linux-kernel - Re: [PATCH] KEYS: trusted: allow module init if TPM is inactive or deactivated

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Date:   Fri, 2 Aug 2019 15:23:44 -0500
From:   Tyler Hicks <tyhicks@...onical.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Roberto Sassu <roberto.sassu@...wei.com>, jejb@...ux.ibm.com,
        zohar@...ux.ibm.com, jgg@...pe.ca, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org, crazyt2019+lml@...il.com,
        nayna@...ux.vnet.ibm.com, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH] KEYS: trusted: allow module init if TPM is inactive or
 deactivated

On 2019-08-02 22:42:26, Jarkko Sakkinen wrote:
> On Fri, Aug 02, 2019 at 09:27:22AM -0500, Tyler Hicks wrote:
> > On 2019-08-02 10:21:16, Roberto Sassu wrote:
> > > On 8/1/2019 6:32 PM, Jarkko Sakkinen wrote:
> > > > On Mon, Jul 15, 2019 at 06:44:28PM +0200, Roberto Sassu wrote:
> > > > > According to the bug report at https://bugs.archlinux.org/task/62678,
> > > > > the trusted module is a dependency of the ecryptfs module. We should
> > > > > load the trusted module even if the TPM is inactive or deactivated.
> > > > > 
> > > > > Given that commit 782779b60faa ("tpm: Actually fail on TPM errors during
> > > > > "get random"") changes the return code of tpm_get_random(), the patch
> > > > > should be modified to ignore the -EIO error. I will send a new version.
> > > > 
> > > > Do you have information where this dependency comes from?
> > > 
> > > ecryptfs retrieves the encryption key from encrypted keys (see
> > > ecryptfs_get_encrypted_key()).
> > 
> > That has been there for many years with any problems. It was added
> > in 2011:
> > 
> >  commit 1252cc3b232e582e887623dc5f70979418caaaa2
> >  Author: Roberto Sassu <roberto.sassu@...ito.it>
> >  Date:   Mon Jun 27 13:45:45 2011 +0200
> > 
> >      eCryptfs: added support for the encrypted key type
> > 
> > What's recently changed the situation is this patch:
> > 
> >  commit 240730437deb213a58915830884e1a99045624dc
> >  Author: Roberto Sassu <roberto.sassu@...wei.com>
> >  Date:   Wed Feb 6 17:24:51 2019 +0100
> > 
> >      KEYS: trusted: explicitly use tpm_chip structure from tpm_default_chip()
> > 
> > Now eCryptfs has a hard dependency on a TPM chip that's working
> > as expected even if eCryptfs (or the rest of the system) isn't utilizing
> > the TPM. If the TPM behaves unexpectedly, you can't access your files.
> > We need to get this straightened out soon.
> 
> I agree with this conclusion that eCryptfs needs to be fixed, not
> another workaround to trusted.ko.

That wasn't the conclusion that I came to. I prefer Robert's proposed
change to trusted.ko.

How do you propose that this be fixed in eCryptfs?

Removing encrypted_key support from eCryptfs is the only way that I can
see to fix the bug in eCryptfs. That support has been there since 2011.
I'm not sure of the number of users that would be broken by removing
encrypted_key support. I don't think the number is high but I can't say
that confidently.

Roberto, what was your use case when you added encrypted_key support to
eCryptfs back then? Are you aware of any users of eCryptfs +
encrypted_keys?

Jarkko, removing a long-standing feature is potentially more disruptive
to users than adding a workaround to trusted.ko which already requires a
similar workaround. I don't think that I agree with you on the proper
fix here.

Tyler

> 
> /Jarkko