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

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Date:	Mon, 22 Dec 2008 20:47:45 -0800
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Oleg Nesterov <oleg@...hat.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()

Eric W. Biederman [ebiederm@...ssion.com] wrote:
| Oleg Nesterov <oleg@...hat.com> writes:
| 
| >> I was going through the ->si_pid assignments to try and fix them at
| >> source (like the mqueue patch I sent last week).
| >
| > OK.
| 
| Note.  When a signal goes to a process group (or similar) we can't fix
| si_pid at the source.  We have to fix it when only a single destination
| process is known.  It doesn't mean that fixing it at the source
| is hopeless but...  

Right. Most calls to kill_pgrp_info() and __kill_pgrp_info() use
SEND_SIG_PRIV or SEND_SIG_NOINFO, so their ->si_pid is set.
The only place seems to be the sys_kill()/sys_tkill().

| 
| >> 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). 

Yes, thats one reason I was thinking of checking si_code == SI_USER or
SI_TKILL, but rt_sigqueueinfo() could still use those values too.

In fact it could use SI_ASYNCIO :-) and mess with sig_from_user() (i.e
if rt_sigqueueinfo() sets si_code to SI_ASYNCIO and sends SIGKILL/SIGSTOP
to a descendant cinit, SIGKILL/SIGSTOP will be ignored).

We could/should warn if rt_sigqueueinfo() sets si_code to SI_ASYNCIO.

One more reason to make SI_ASYNCIO a kernel signal I guess.

| 
| Yes.  I don't think si_pid is valid in that case anyway.  It is the
| kernel signals where si_pid is a reliable field that are important.
| 
| Eric

Sukadev
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