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

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Date:   Tue, 7 Nov 2017 13:06:48 -0500
From:   Matthew Garrett <mjg59@...gle.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     linux-integrity <linux-integrity@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH v2 00/15] ima: digest list feature

On Tue, Nov 7, 2017 at 12:53 PM, Roberto Sassu <roberto.sassu@...wei.com> wrote:
> On 11/7/2017 3:49 PM, Matthew Garrett wrote:
>> RPM's hardly universal, and distributions are in the process of moving
>> away from using it for distributing non-core applications (Flatpak and
>> Snap are becoming increasingly popular here). I think this needs to be
>> a generic solution rather than having the kernel tied to a specific
>> package format.
>
>
> Support for new digest list formats can be easily added. Digest list
> metadata includes the digest list type, so that the appropriate parser
> is selected.

But we're still left in a state where the kernel has to end up
supporting a number of very niche formats, and userland agility is
tied to the kernel. I think it makes significantly more sense to push
the problem out to userland.

> Digest lists should be parsed directly by the kernel, because processing
> the lists in userspace would increase the chances that a compromised
> tool does not upload to the kernel the expected digests. Also, digest
> lists must be processed before init, otherwise appraisal will deny the
> execution. Lastly, the mechanism of parsing files from the kernel is
> already used to parse the IMA policy.

Isn't failing to upload the expected digest list just a DoS? We
already expect to load keys from initramfs, so it seems fine to parse
stuff there - what's the problem with extracting information from
RPMs, translating them to the generic format and pushing that into the
kernel?