linux-kernel - Re: [PATCH v2 5/8] ima: Switch to dynamically allocated buffer for template digests

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Message-Id: <1581006834.5585.430.camel@linux.ibm.com>
Date:   Thu, 06 Feb 2020 11:33:54 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>,
        "James.Bottomley@...senPartnership.com" 
        <James.Bottomley@...senPartnership.com>,
        "jarkko.sakkinen@...ux.intel.com" <jarkko.sakkinen@...ux.intel.com>
Cc:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Silviu Vlasceanu <Silviu.Vlasceanu@...wei.com>
Subject: Re: [PATCH v2 5/8] ima: Switch to dynamically allocated buffer for
 template digests

On Thu, 2020-02-06 at 16:27 +0000, Roberto Sassu wrote:
> > -----Original Message-----
> > From: Mimi Zohar [mailto:zohar@...ux.ibm.com]
> > Sent: Thursday, February 6, 2020 5:08 PM
> > To: Roberto Sassu <roberto.sassu@...wei.com>;
> > James.Bottomley@...senPartnership.com;
> > jarkko.sakkinen@...ux.intel.com
> > Cc: linux-integrity@...r.kernel.org; linux-security-module@...r.kernel.org;
> > linux-kernel@...r.kernel.org; Silviu Vlasceanu
> > <Silviu.Vlasceanu@...wei.com>
> > Subject: Re: [PATCH v2 5/8] ima: Switch to dynamically allocated buffer for
> > template digests
> > 
> > Hi Roberto,
> > 
> > On Wed, 2020-02-05 at 11:33 +0100, Roberto Sassu wrote:
> > > This patch dynamically allocates the array of tpm_digest structures in
> > > ima_alloc_init_template() and ima_restore_template_data(). The size of
> > the
> > > array, stored in ima_num_template_digests, is initially equal to 1 (SHA1)
> > > and will be determined in the upcoming patches depending on the
> > allocated
> > > PCR banks and the chosen default IMA algorithm.
> > >
> > > Calculating the SHA1 digest is mandatory, as SHA1 still remains the default
> > > hash algorithm for the measurement list. When IMA will support the
> > Crypto
> > > Agile format, remaining digests will be also provided.
> > >
> > > The position in the array of the SHA1 digest is stored in the ima_sha1_idx
> > > global variable and it is determined at IMA initialization time.
> > >
> > > Changelog
> > >
> > > v1:
> > > - move ima_sha1_idx to ima_crypto.c
> > > - introduce ima_num_template_digests (suggested by Mimi)
> > 
> > Instead of hardcoding "nr_allocated_banks + 1" or nr_allocated_banks +
> > 2", I suggested defining "nr_allocated_banks + extra", where "extra"
> > could be 0, 1, or 2.
> > 
> > The rest of the code would remain exactly the same as you had.
> 
> Ok. I did a small improvement. Since we determine the number of
> required elements of ima_algo_array before kmalloc() I thought it
> was ok to directly set that number of elements in a single variable.
> 
> If you think that having two variables is better, I will change it.

The connection to nr_allocated_banks is then not as visible.  Using
two variables is clearer.

Mimi