linux-kernel - Re: [RFC][PATCH 01/12] ima: Add digest, algo, measured parameters to ima_measure_critical

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Date:   Fri, 25 Jun 2021 14:26:55 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        selinux@...r.kernel.org, Prakhar Srivastava <prsriva02@...il.com>,
        Tushar Sugandhi <tusharsu@...ux.microsoft.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Subject: Re: [RFC][PATCH 01/12] ima: Add digest, algo, measured parameters
 to ima_measure_critical_data()

On Fri, 2021-06-25 at 18:56 +0200, Roberto Sassu wrote:
> ima_measure_critical_data() allows any caller in the kernel to provide a
> buffer, so that is measured by IMA if an appropriate policy is set. Some
> information that could be useful to the callers are the digest of the
> buffer included in the new measurement entry, the digest algorithm and
> whether the buffer was measured.
> 
> This patch modifies the definition of ima_measure_critical_data() to
> include three new parameters: digest, algo and measured. If they are NULL,
> the function behaves as before and just measures the buffer, if requested
> with the IMA policy. Otherwise, it also writes the digest, algorithm and
> whether the buffer is measured to the provided pointers.
> 
> If the pointers are not NULL, the digest is calculated also if there is no
> matching rule in the IMA policy.

As much as possible, let's not define additional
ima_measure_critical_data() arguments.  Probably the only new variable
really need is "digest".  The hash algorithm doesn't change.  How about
defining and exporting a new function to return the system defined
ima_hash_algo.  In terms of failure, have ima_measure_critical_data()
return errno.

thanks,

Mimi