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

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Date:   Wed, 1 Aug 2018 09:56:41 +0200
From:   Jann Horn <jannh@...gle.com>
To:     j@...ron.ch
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linux API <linux-api@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] prctl: add PR_[GS]ET_KILLABLE

On Wed, Aug 1, 2018 at 9:44 AM Jürg Billeter <j@...ron.ch> wrote:
>
> On Tue, 2018-07-31 at 18:26 +0200, Jann Horn wrote:
> > On Mon, Jul 30, 2018 at 10:01 AM Jürg Billeter <j@...ron.ch> wrote:
> >
> > [...]
> > > diff --git a/kernel/sys.c b/kernel/sys.c
> > > index 38509dc1f77b..264de630d548 100644
> > > --- a/kernel/sys.c
> > > +++ b/kernel/sys.c
> >
> > [...]
> > > +       case PR_SET_KILLABLE:
> > > +               if (arg2 != 1 || arg3 || arg4 || arg5)
> > > +                       return -EINVAL;
> > > +               me->signal->flags &= ~SIGNAL_UNKILLABLE;
> > > +               break;
> >
> > I don't have an opinion on this patchset otherwise, but should this
> > prctl maybe block PR_SET_KILLABLE if you're actually the real init
> > process? This seems like it could potentially lead to weird things.
>
> While I don't expect global init to use this, I can't think of a good
> reason to disallow it in the kernel. Do you have specific concerns or
> is the code in kernel/fork.c the only reason?

No, I don't have any other specific concerns.

> I prefer avoiding special cases unless really required.