linux-kernel - Re: [PATCH v2 1/4] Landlock: Add signal control

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Message-ID: <CAG48ez3nx4fR7skDf_Vhgm3OLJqGtsLUgHQMykq7oy9HZq5fgw@mail.gmail.com>
Date: Fri, 9 Aug 2024 15:57:21 +0200
From: Jann Horn <jannh@...gle.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: Tahera Fahimi <fahimitahera@...il.com>, outreachy@...ts.linux.dev, gnoack@...gle.com, 
	paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com, 
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org, 
	bjorn3_gh@...tonmail.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2 1/4] Landlock: Add signal control

On Fri, Aug 9, 2024 at 3:37 PM Mickaël Salaün <mic@...ikod.net> wrote:
> On Fri, Aug 09, 2024 at 02:44:06PM +0200, Jann Horn wrote:
> > On Fri, Aug 9, 2024 at 12:59 PM Mickaël Salaün <mic@...ikod.net> wrote:
> > > On Thu, Aug 08, 2024 at 04:42:23PM +0200, Jann Horn wrote:
[...]
> > > > So if you want to use RCU lifetime for this, I think you'll have to
> > > > turn landlock_put_ruleset() and landlock_put_ruleset_deferred() into
> > > > one common function that always, when reaching refcount 0, schedules
> > > > an RCU callback which then schedules a work_struct which then does
> > > > free_ruleset().
> > > >
> > > > I think that would be a little ugly, and it would look nicer to just
> > > > use normal locking in the file_send_sigiotask hook?
> > >
> > > I don't see how we can do that without delaying the free_ruleset() call
> > > to after the RCU read-side critical section in f_setown().
> >
> > It should work if you used landlock_put_ruleset_deferred() instead of
> > landlock_put_ruleset().
>
> Calling landlock_put_ruleset_deferred() in hook_file_set_fowner() or
> replacing all landlock_put_ruleset() calls?

Calling landlock_put_ruleset_deferred() in hook_file_set_fowner().

> The deferred work queue is not guarantee to run after all concurrent RCU
> read-side critical sections right?

Yes, I was talking about my "it would look nicer to just use normal
locking in the file_send_sigiotask hook" suggestion - don't use any
RCU stuff, just use the same lock in file_set_fowner and
file_send_sigiotask.