linux-kernel - Re: [PATCH v5 23/23] integrity: Switch from rbtree to LSM-managed blob for integrity_iint

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Date:   Thu, 30 Nov 2023 08:15:17 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Petr Tesarik <petrtesarik@...weicloud.com>,
        Roberto Sassu <roberto.sassu@...weicloud.com>,
        Paul Moore <paul@...l-moore.com>
Cc:     viro@...iv.linux.org.uk, brauner@...nel.org,
        chuck.lever@...cle.com, jlayton@...nel.org, neilb@...e.de,
        kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
        jmorris@...ei.org, serge@...lyn.com, zohar@...ux.ibm.com,
        dmitry.kasatkin@...il.com, dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        mic@...ikod.net, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        selinux@...r.kernel.org, Roberto Sassu <roberto.sassu@...wei.com>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v5 23/23] integrity: Switch from rbtree to LSM-managed
 blob for integrity_iint_cache

On 11/30/2023 12:30 AM, Petr Tesarik wrote:
> Hi all,
>
> On 11/30/2023 1:41 AM, Casey Schaufler wrote:
>> ...
>> It would be nice if the solution directly addresses the problem.
>> EVM needs to be after the LSMs that use xattrs, not after all LSMs.
>> I suggested LSM_ORDER_REALLY_LAST in part to identify the notion as
>> unattractive.
> Excuse me to chime in, but do we really need the ordering in code?

tl;dr - Yes.

>  FWIW
> the linker guarantees that objects appear in the order they are seen
> during the link (unless --sort-section overrides that default, but this
> option is not used in the kernel). Since *.a archive files are used in
> kbuild, I have also verified that their use does not break the
> assumption; they are always created from scratch.
>
> In short, to enforce an ordering, you can simply list the corresponding
> object files in that order in the Makefile. Of course, add a big fat
> warning comment, so people understand the order is not arbitrary.

Not everyone builds custom kernels.

>
> Just my two eurocents,
> Petr T
>
>