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Date:   Thu, 13 Aug 2020 10:56:17 -0400
From:   Chuck Lever <>
To:     James Bottomley <>
Cc:     Mimi Zohar <>, James Morris <>,
        Deven Bowers <>,
        Pavel Machek <>, Sasha Levin <>,,,,,
        Paul Moore <>,
        Jonathan Corbet <>,,,,
        Jann Horn <>,,
        Al Viro <>,
        Jens Axboe <>,,
        open list <>,,,,
        linux-fsdevel <>,,
Subject: Re: [dm-devel] [RFC PATCH v5 00/11] Integrity Policy Enforcement LSM

> On Aug 13, 2020, at 10:42 AM, James Bottomley <> wrote:
> On Thu, 2020-08-13 at 10:21 -0400, Chuck Lever wrote:
>>> On Aug 12, 2020, at 11:42 AM, James Bottomley <James.Bottomley@...s
>>>> wrote:
> [...]
>>> For most people the security mechanism of local xattrs is
>>> sufficient.  If you're paranoid, you don't believe it is and you
>>> use EVM.
>> When IMA metadata happens to be stored in local filesystems in
>> a trusted xattr, it's going to enjoy the protection you describe
>> without needing the addition of a cryptographic signature.
>> However, that metadata doesn't live its whole life there. It
>> can reside in a tar file, it can cross a network, it can live
>> on a back-up tape. I think we agree that any time that metadata
>> is in transit or at rest outside of a Linux local filesystem, it
>> is exposed.
>> Thus I'm interested in a metadata protection mechanism that does
>> not rely on the security characteristics of a particular storage
>> container. For me, a cryptographic signature fits that bill
>> nicely.
> Sure, but one of the points about IMA is a separation of mechanism from
> policy.  Signed hashes (called appraisal in IMA terms) is just one
> policy you can decide to require or not or even make it conditional on
> other things.

AFAICT, the current EVM_IMA_DIGSIG and EVM_PORTABLE_DIGSIG formats are
always signed. The policy choice is whether or not to verify the
signature, not whether or not the metadata format is signed.

Chuck Lever

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