linux-kernel - Re: [PATCH v2] prctl: add PR_[GS]ET

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Date:   Wed, 1 Aug 2018 16:19:15 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Jürg Billeter <j@...ron.ch>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Biederman <ebiederm@...ssion.com>,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] prctl: add PR_[GS]ET_KILLABLE

On 07/31, Jürg Billeter wrote:
>
> > Could you explain your use-case? Why a shell wants to use
> > CLONE_NEWPID?
>
> To guarantee that there won't be any runaway processes, i.e., ensure
> that no descendants (background helper daemons or misbehaving
> processes) survive when the child process is terminated.

We already have PR_SET_CHILD_SUBREAPER.

Perhaps we can finally add PR_KILL_MY_DESCENDANTS_ON_EXIT? This was already
discussed some time ago, but I can't find the previous discussion... Simple
to implement.

> And to prevent
> children from killing their ancestors.

OK, this is the only reason for CLONE_NEWPID which I can understand so far.
Not that I understand why this is that useful ;)

> > >  * As SIGSTOP is ignored when raised from the SIGNAL_UNKILLABLE process
> > >    itself, it's not possible to implement the stop action in a custom
> > >    SIGTSTP handler.
> >
> > Yes. So may be we actually want to change __isig() paths to use
> > SEND_SIG_FORCED (this is not that simple), or perhaps we can change
> > __send_signal() to not drop SIGSTOP sent to itself, or may be we can even
> > introduce SIG_DFL_EVEN_IF_INIT, I dunno.
>
> In my opinion, my patch is much simpler and also more general as it

Yes, yes, let me repeat that I am not arguing with your patch, I am just trying
to understand what

> > I can't understand this. An application should be changed anyway to do
> > PR_SET_KILLABLE?
>
> PR_SET_KILLABLE can be called (e.g., by the shell) between clone() and
> execve().

OK, this is true.

Oleg.