linux-kernel - Re: [PATCH] ima: drop vla in ima_audit

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Message-Id: <1520535030.3605.64.camel@linux.vnet.ibm.com>
Date:   Thu, 08 Mar 2018 13:50:30 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     Tycho Andersen <tycho@...ho.ws>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        linux-integrity@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] ima: drop vla in ima_audit_measurement()

On Thu, 2018-03-08 at 11:37 -0700, Tycho Andersen wrote:
> On Thu, Mar 08, 2018 at 07:47:37PM +0200, Andy Shevchenko wrote:
> > On Thu, Mar 8, 2018 at 7:14 PM, Tycho Andersen <tycho@...ho.ws> wrote:
> > > In keeping with the directive to get rid of VLAs [1], let's drop the VLA
> > > from ima_audit_measurement(). We need to adjust the return type of
> > > ima_audit_measurement, because now this function can fail if an allocation
> > > fails.
> > 
> > 
> > 
> > > +       algo_hash_len = hash_len + strlen(algo_name) + 2;
> > > +       algo_hash = kzalloc(algo_hash_len, GFP_KERNEL);
> > 
> > > -       snprintf(algo_hash, sizeof(algo_hash), "%s:%s", algo_name, hash);
> > > +       snprintf(algo_hash, algo_hash_len, "%s:%s", algo_name, hash);
> > 
> > kasprintf() ?
> 
> Sure, in fact I think we could just do:
> 
> -	snprintf(algo_hash, algo_hash_len, "%s:%s", algo_name, hash);
> -	audit_log_untrustedstring(ab, algo_hash);
> +	audit_log_untrustedstring(ab, algo_name);
> +	audit_log_format(ab, ":");
> +	audit_log_untrustedstring(ab, hash);
> 
> and get rid of the allocation entirely. I'll test and make sure it
> works and then re-send.

The hash algorithm name is an enumeration that comes from the kernel.
 It's defined in crypto/hash_info.c: hash_algo_name.  Why do we need
to use audit_log_untrustedstring()?

Mimi