linux-kernel - Re: [PATCH v9 13/25] security: Introduce file

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Message-ID: <00b7ff22-f213-471a-a604-658a9af80d59@schaufler-ca.com>
Date: Tue, 16 Jan 2024 08:51:11 -0800
From: Casey Schaufler <casey@...aufler-ca.com>
To: Roberto Sassu <roberto.sassu@...weicloud.com>,
 Al Viro <viro@...iv.linux.org.uk>
Cc: brauner@...nel.org, chuck.lever@...cle.com, jlayton@...nel.org,
 neilb@...e.de, kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
 paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
 zohar@...ux.ibm.com, dmitry.kasatkin@...il.com, eric.snowberg@...cle.com,
 dhowells@...hat.com, jarkko@...nel.org, stephen.smalley.work@...il.com,
 eparis@...isplace.org, shuah@...nel.org, mic@...ikod.net,
 linux-kernel@...r.kernel.org, linux-fsdevel@...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, linux-kselftest@...r.kernel.org,
 Roberto Sassu <roberto.sassu@...wei.com>,
 Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v9 13/25] security: Introduce file_release hook

On 1/16/2024 12:47 AM, Roberto Sassu wrote:
> On Mon, 2024-01-15 at 19:15 +0000, Al Viro wrote:
>> On Mon, Jan 15, 2024 at 07:17:57PM +0100, Roberto Sassu wrote:
>>> From: Roberto Sassu <roberto.sassu@...wei.com>
>>>
>>> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
>>> the file_release hook.
>>>
>>> IMA calculates at file close the new digest of the file content and writes
>>> it to security.ima, so that appraisal at next file access succeeds.
>>>
>>> An LSM could implement an exclusive access scheme for files, only allowing
>>> access to files that have no references.
>> Elaborate that last part, please.
> Apologies, I didn't understand that either. Casey?

Just a hypothetical notion that if an LSM wanted to implement an
exclusive access scheme it might find the proposed hook helpful.
I don't have any plan to create such a scheme, nor do I think that
a file_release hook would be the only thing you'd need.

>
> Thanks
>
> Roberto
>