linux-kernel - Re: Potentially undesirable interactions between vfork() and time namespaces

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Date:   Fri, 2 Sep 2022 10:20:57 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Alexey Izbyshev <izbyshev@...ras.ru>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Florian Weimer <fweimer@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: Potentially undesirable interactions between vfork() and time
 namespaces

On Fri, Sep 02, 2022 at 07:39:28PM +0300, Alexey Izbyshev wrote:

<snip>

> > > @@ -2043,18 +2043,6 @@ static __latent_entropy struct task_struct
> > > *copy_process(
> > >  			return ERR_PTR(-EINVAL);
> > >  	}
> > > 
> > > -	/*
> > > -	 * If the new process will be in a different time namespace
> > > -	 * do not allow it to share VM or a thread group with the forking
> > > task.
> > > -	 *
> > > -	 * On vfork, the child process enters the target time namespace only
> > > -	 * after exec.
> > > -	 */
> > > -	if ((clone_flags & (CLONE_VM | CLONE_VFORK)) == CLONE_VM) {
> > > -		if (nsp->time_ns != nsp->time_ns_for_children)
> > > -			return ERR_PTR(-EINVAL);
> > > -	}
> > 
> > pls don't remove this part. It was one of the concerns that vfork
> > doesn't work after unshare(CLONE_NEWTIME), but it is one of the standard
> > ways of creating a new process. For example, posix_spawn uses it.
> > 
> What do you mean? On the contrary, removing this restriction of the original
> time namespace implementation allows vfork(), pthread_create() and the like,
> solving the issue with posix_spawn() as well.
>

Sorry, I was not woken up completely and decided that it just reverted
the change that allows vfork. Now, I see that it removes this
restriction completely. So it looks good to me.

Thanks,
Andrei.