Re: [PATCH] exec: fix the racy usage of fs_struct->in_exec

[Oleg Nesterov <oleg@redhat.com>]

On 03/24, Mateusz Guzik wrote:
>
> On Mon, Mar 24, 2025 at 7:28 PM Oleg Nesterov <oleg@redhat.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?

> Anyhow, the plan would be to serialize on the bit, synchronized with
> the current spin lock. copy_fs would call a helper to wait for it to
> clear, would still bump ->users under the spin lock.
>
> This would decouple the handling from cred_mutex and avoid weirdness
> like clearing the ->in_exec flag when we never set it.

I don't really understand the idea, but as I said I won't argue with
another solution.

Oleg.