linux-kernel - Re: f_modown and LSM inconsistency (was [PATCH v2 1/4] Landlock: Add signal control)

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Message-ID: <CAHC9VhS6=s9o4niaLzkDG6Egir4WL=ieDdyeKk4qzQo1WFi=WQ@mail.gmail.com>
Date: Mon, 12 Aug 2024 10:57:37 -0400
From: Paul Moore <paul@...l-moore.com>
To: Jann Horn <jannh@...gle.com>
Cc: Mickaël Salaün <mic@...ikod.net>, 
	Christian Brauner <brauner@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, 
	Casey Schaufler <casey@...aufler-ca.com>, Tahera Fahimi <fahimitahera@...il.com>, gnoack@...gle.com, 
	jmorris@...ei.org, serge@...lyn.com, linux-security-module@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: f_modown and LSM inconsistency (was [PATCH v2 1/4] Landlock: Add
 signal control)

On Mon, Aug 12, 2024 at 9:09 AM Jann Horn <jannh@...gle.com> wrote:
> On Mon, Aug 12, 2024 at 12:04 AM Paul Moore <paul@...l-moore.com> wrote:

...

> > From a LSM perspective I suspect we are always going to need some sort
> > of hook in the F_SETOWN code path as the LSM needs to potentially
> > capture state/attributes/something-LSM-specific at that
> > context/point-in-time.
>
> The only thing LSMs currently do there is capture state from
> current->cred. So if the VFS takes care of capturing current->cred
> there, we should be able to rip out all the file_set_fowner stuff.
> Something like this (totally untested):

I've very hesitant to drop the LSM hook from the F_SETOWN path both
because it is reasonable that other LSMs may want to do other things
here, and adding a LSM hook to the kernel, even if it is re-adding a
hook that was previously removed, is a difficult and painful process
with an uncertain outcome.

-- 
paul-moore.com