linux-kernel - Re: [PATCH] exec: fix the racy usage of fs_struct->in

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Message-ID: <20250325-bretter-anfahren-39ee9eedf048@brauner>
Date: Tue, 25 Mar 2025 14:30:48 +0100
From: Christian Brauner <brauner@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>, Mateusz Guzik <mjguzik@...il.com>
Cc: syzbot <syzbot+1c486d0b62032c82a968@...kaller.appspotmail.com>, 
	kees@...nel.org, viro@...iv.linux.org.uk, jack@...e.cz, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] exec: fix the racy usage of fs_struct->in_exec

On Tue, Mar 25, 2025 at 02:21:36PM +0100, Oleg Nesterov wrote:
> On 03/25, Mateusz Guzik wrote:
> >
> > On Tue, Mar 25, 2025 at 11:10 AM Oleg Nesterov <oleg@...hat.com> wrote:
> > >
> > > On 03/24, Mateusz Guzik wrote:
> > > >
> > > > On Mon, Mar 24, 2025 at 7:28 PM Oleg Nesterov <oleg@...hat.com> wrote:
> > > > >
> > > > > So to me it would be better to have the trivial fix for stable,
> > > > > exactly because it is trivially backportable. Then cleanup/simplify
> > > > > this logic on top of it.
> > > >
> > > > So I got myself a crap testcase with a CLONE_FS'ed task which can
> > > > execve and sanity-checked that suid is indeed not honored as expected.
> > >
> > > So you mean my patch can't fix the problem?
> >
> > No, I think the patch works.
> >
> > I am saying the current scheme is avoidably hard to reason about.
> 
> Ah, OK, thanks. Then I still think it makes more sense to do the
> cleanups you propose on top of this fix.

I agree. We should go with Oleg's fix that in the old scheme and use
that. And then @Mateusz your cleanup should please go on top!