linux-kernel - Re: [PATCH v3 09/10] certs: Allow root user to append signed hashes to the blacklist keyring

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Message-ID: <e1c072eba237e75fc687e9318f65e7395e2ca00b.camel@linux.ibm.com>
Date:   Fri, 15 Jan 2021 08:06:57 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Mickaël Salaün <mic@...ikod.net>,
        David Howells <dhowells@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Jarkko Sakkinen <jarkko@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        James Morris <jmorris@...ei.org>,
        Mickaël Salaün <mic@...ux.microsoft.com>,
        "Serge E . Hallyn" <serge@...lyn.com>, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH v3 09/10] certs: Allow root user to append signed hashes
 to the blacklist keyring

Hi Mickaël,

On Thu, 2021-01-14 at 16:19 +0100, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@...ux.microsoft.com>
> 
> Add a kernel option SYSTEM_BLACKLIST_AUTH_UPDATE to enable the root user
> to dynamically add new keys to the blacklist keyring.  This enables to
> invalidate new certificates, either from being loaded in a keyring, or
> from being trusted in a PKCS#7 certificate chain.  This also enables to
> add new file hashes to be denied by the integrity infrastructure.
> 
> Being able to untrust a certificate which could have normaly been
> trusted is a sensitive operation.  This is why adding new hashes to the
> blacklist keyring is only allowed when these hashes are signed and
> vouched by the builtin trusted keyring.  A blacklist hash is stored as a
> key description.  The PKCS#7 signature of this description must be
> provided as the key payload.
> 
> Marking a certificate as untrusted should be enforced while the system
> is running.  It is then forbiden to remove such blacklist keys.
> 
> Update blacklist keyring and blacklist key access rights:
> * allows the root user to search for a specific blacklisted hash, which
>   make sense because the descriptions are already viewable;
> * forbids key update;
> * restricts kernel rights on the blacklist keyring to align with the
>   root user rights.
> 
> See the help in tools/certs/print-cert-tbs-hash.sh provided by a
> following commit.

The design looks good.  I'm hoping to review/test at least this patch
next week.

thanks,

Mimi