linux-kernel - Re: Signals to cinit

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Date:	Wed, 12 Nov 2008 17:12:34 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	sukadev@...ux.vnet.ibm.com
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...nvz.org>, daniel@...ac.com,
	Nadia Derbey <Nadia.Derbey@...l.net>, serue@...ibm.com,
	clg@...ibm.com, Containers <containers@...ts.osdl.org>,
	sukadev@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: Signals to cinit

On 11/12, Oleg Nesterov wrote:
>
> On 11/10, sukadev@...ux.vnet.ibm.com wrote:
> >
> > Oleg Nesterov [oleg@...hat.com] wrote:
> > | > Or something. yes, sys_rt_sigqueueinfo() is problematic...
> >
> > Yes, if user-space sets si_pid to 0.
> >
> > Can we change sys_rt_sigqueueinfo() to:
> >
> > 	if (!info->si_pid)
> > 		info->si_pid = getpid();
>
> I doubt very much we can do this. This can break the existing applications
> which can overload ->si_pid. I think it is better to pass ->si_pid as is.
> If user-space sends siginfo_t so sub-namespace, it must know what it does.
> I don't think the kernel can help, it just can't know what ->si_pid actually
> means. Unless this is documented somewhere, but I don't know.

On the second thought, I think perhaps we should do the following.

if sys_rt_sigqueueinfo() sends the signal to the sub-namespace, then clear
always ->sid_pid. Otherwise do not touch it.

This way we can't break the existing apps, and this simplifies send_signal()
which should take "is_it_from_ancestor_ns" into account.

What do you think?

Oleg.

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