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

[Roberto Sassu]

On 11/17/2017 2:08 AM, Kees Cook wrote:
> On Tue, Nov 7, 2017 at 8:45 AM, Roberto Sassu <roberto.sassu@xxxxxxxxxx> 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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