linux-kernel - Re: [PATCH v4] KEYS: encrypted: Instantiate key with user-provided decrypted data

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Message-ID: <CAFA6WYOJt3=YMTt_QQSq6Z-MK42hwWspgSpasw2fuPtVFcP3uA@mail.gmail.com>
Date:   Mon, 3 Jan 2022 12:21:04 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Yael Tiomkin <yaelt@...gle.com>, linux-integrity@...r.kernel.org,
        jejb@...ux.ibm.com, jarkko@...nel.org, corbet@....net,
        dhowells@...hat.com, jmorris@...ei.org, serge@...lyn.com,
        keyrings@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Jan Lübbe <jlu@...gutronix.de>,
        Ahmad Fatoum <a.fatoum@...gutronix.de>
Subject: Re: [PATCH v4] KEYS: encrypted: Instantiate key with user-provided
 decrypted data

Hi Mimi,

Apologies for the delayed reply as I was on leave for a long new year weekend.

On Thu, 30 Dec 2021 at 18:59, Mimi Zohar <zohar@...ux.ibm.com> wrote:
>
> Hi Sumit,
>
> On Thu, 2021-12-30 at 15:37 +0530, Sumit Garg wrote:
> > + Jan, Ahmad
> >
> > On Thu, 30 Dec 2021 at 03:24, Yael Tiomkin <yaelt@...gle.com> wrote:
> > >
> > > The encrypted.c class supports instantiation of encrypted keys with
> > > either an already-encrypted key material, or by generating new key
> > > material based on random numbers. This patch defines a new datablob
> > > format: [<format>] <master-key name> <decrypted data length>
> > > <decrypted data> that allows to instantiate encrypted keys using
> > > user-provided decrypted data, and therefore allows to perform key
> > > encryption from userspace. The decrypted key material will be
> > > inaccessible from userspace.
> >
> > This type of user-space key import feature has already been discussed
> > at large in the context of trusted keys here [1]. So what makes it
> > special in case of encrypted keys such that it isn't a "UNSAFE_IMPORT"
> > or "DEBUGGING_IMPORT" or "DEVELOPMENT_IMPORT", ...?
> >
> > [1] https://lore.kernel.org/linux-integrity/74830d4f-5a76-8ba8-aad0-0d79f7c01af9@pengutronix.de/
> >
> > -Sumit
> >
> > >
> > > Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> > > Signed-off-by: Yael Tiomkin <yaelt@...gle.com>
>
> There is a difference between trusted and encrypted keys.

Yeah I understand the implementation differences.

>  So in
> addition to pointing to the rather long discussion thread, please
> summarize the conclusion and, assuming you agree, include why in once
> case it was acceptable and in the other it wasn't to provide userspace
> key data.

My major concern with importing user-space key data in *plain* format
is that if import is *not* done in a safe (manufacturing or
production) environment then the plain key data is susceptible to
user-space compromises when the device is in the field.

And it sounds like we are diverting from basic definition [1] of encrypted keys:

"Trusted and Encrypted Keys are two new key types added to the
existing kernel key ring service. Both of these new types are variable
length symmetric keys, and in both cases all keys are created in the
kernel, and **user space sees, stores, and loads** only encrypted
blobs."

Also, as Jarrko mentioned earlier the use-case is still not clear to
me as well. Isn't user logon keys an alternative option for
non-readable user-space keys?

[1] https://www.kernel.org/doc/html/v4.13/security/keys/trusted-encrypted.html

-Sumit

>
> thanks,
>
> Mimi
>