linux-kernel - Re: [PATCH v4 1/3] ima: Introduce ima_get_current_hash

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Date:   Fri, 23 Jul 2021 08:49:08 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>, paul@...l-moore.com
Cc:     stephen.smalley.work@...il.com, prsriva02@...il.com,
        tusharsu@...ux.microsoft.com, nramas@...ux.microsoft.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH v4 1/3] ima: Introduce ima_get_current_hash_algo()

On Fri, 2021-07-23 at 10:53 +0200, Roberto Sassu wrote:
> Buffer measurements, unlike file measurements, are not accessible after the
> measurement is done, as buffers are not suitable for use with the
> integrity_iint_cache structure (there is no index, for files it is the
> inode number). In the subsequent patches, the measurement (digest) will be
> returned directly by the functions that perform the buffer measurement,
> ima_measure_critical_data() and process_buffer_measurement().
> 
> A caller of those functions also needs to know the algorithm used to
> calculate the digest. Instead of adding the algorithm as a new parameter to
> the functions, this patch provides it separately with the new function
> ima_get_current_hash_algo().
> 
> Since the hash algorithm does not change after the IMA setup phase, there
> is no risk of races (obtaining a digest calculated with a different
> algorithm than the one returned).

Perfect explaination for annotating ima_hash_algo like:

int __ro_after_init ima_hash_algo = HASH_ALGO_SHA1;

Assuming you don't object, I'll include this change in this patch.

thanks,

Mimi

> 
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> Reviewed-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>