linux-kernel - Re: [PATCH v2 00/15] ima: digest list feature

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Date:   Fri, 17 Nov 2017 09:55:29 +0100
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        <linux-integrity@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        <silviu.vlasceanu@...wei.com>
Subject: Re: [PATCH v2 00/15] ima: digest list feature

On 11/17/2017 2:08 AM, Kees Cook wrote:
> On Tue, Nov 7, 2017 at 8:45 AM, Roberto Sassu <roberto.sassu@...wei.com> wrote:
>> On 11/7/2017 2:37 PM, Mimi Zohar wrote:
>>> Normally, the protection of kernel memory is out of scope for IMA.
>>> This patch set introduces an in kernel white list, which would be a
>>> prime target for attackers looking for ways of by-passing IMA-
>>> measurement, IMA-appraisal and IMA-audit.  Others might disagree, but
>>> from my perspective, this risk is too high.
> 
> BTW, which part of the series does the whitelist? I'd agree generally,
> though: we don't want to make things writable if they're normally
> read-only.

Patch 5/15 introduces the hash table ima_digests_htable and the
functions to add/search file digests

Patches 6-7-8/15 add file digests to ima_digests_htable

Patch 10/15 searches file digests in ima_digests_htable


Original files containing digest lists are discarded after being parsed.


>> It would be much easier for an attacker to just set ima_policy_flag to
>> zero.
> 
> That's a fair point. I wonder if ima_policy_flag could be marked
> __ro_after_init? Most of the writes are from __init sections, but I
> haven't looked closely at when ima_update_policy() gets called.

Unfortunately not. New policies can be loaded by writing to a file in
the securityfs filesystem. They could enable different actions
(measurement/appraisal/audit).

Roberto

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