linux-kernel - Re: [RFC][PATCH 4/6][v3] Define siginfo_from_ancestor

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Message-ID: <20081223002215.GA7984@redhat.com>
Date:	Tue, 23 Dec 2008 01:22:15 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	ebiederm@...ssion.com, roland@...hat.com, bastian@...di.eu.org,
	daniel@...ac.com, xemul@...nvz.org, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org, sukadev@...ibm.com
Subject: Re: [RFC][PATCH 4/6][v3] Define siginfo_from_ancestor_ns()

On 12/22, Sukadev Bhattiprolu wrote:
>
> Oleg Nesterov [oleg@...hat.com] wrote:
> | On 12/22, Oleg Nesterov wrote:
> | >
> | > On 12/20, Sukadev Bhattiprolu wrote:
> | > >
> | > > + * TODO:
> | > > + * 	  Making SI_ASYNCIO a kernel signal could make this less hacky.
> | > > + */
> | > > +#ifdef CONFIG_PID_NS
> | > > +static inline int siginfo_from_user(siginfo_t *info)
> | > > +{
> | > > +	if (!is_si_special(info) && SI_FROMUSER(info) &&
> | >
> | > OK, if we can trust SI_FROMUSER(), then it is better, i agree.
> |
> | Aaah, forgot to mention...
> |
> | But could you explain how are you going to fix another problem,
> | .si_pid mangling? This was another reason for (yes, ugly, agreed)
> | SIG_FROM_USER in .si_signo.
>
> Good point.
>
> I was going through the ->si_pid assignments to try and fix them at
> source (like the mqueue patch I sent last week).

OK.

> The two cases that don't fit the model are sys_kill() and sys_tkill().
> For that I was hoping we could use siginfo_from_user() again. i.e
>
> 	if (siginfo_from_user())
> 		masquerade_si_pid()
>
> in the default: case of send_signal(). To be safe, masquerade_si_pid()
> could do it only iff si_code is either SI_USER or SI_TKILL.
>
> IOW, with some tweaks, I am trying to see if we can use siginfo_from_user()
> in place of the SIG_FROM_USER.

sys_rt_sigqueueinfo().

But, perhaps we can just ignore the problems with sigqueueinfo() (and
document them). The only thing we must preserve is: we should not
change *info when from_parent_ns == F, but this happens "automatically".

And, the kernel just can not know what "info" means when it is sent
by sigqueueinfo() anyway. So, perhaps we can just do

	if (!same_ns)
		masquerade_si_pid()

?

Oleg.

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