linux-kernel - Re: [PATCH] user namespace: make signal.c respect user namespaces

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Date:	Tue, 20 Sep 2011 13:53:54 -0500
From:	"Serge E. Hallyn" <serge.hallyn@...onical.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, richard@....at,
	Andrew Morton <akpm@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tejun Heo <tj@...nel.org>, serge@...lyn.com
Subject: Re: [PATCH] user namespace: make signal.c respect user namespaces

Quoting Oleg Nesterov (oleg@...hat.com):
> On 09/19, Serge E. Hallyn wrote:
> >
> > __send_signal: convert the uid being sent in SI_USER to the target task's
> > user namespace.
> >
> > do_notify_parent and do_notify_parent_cldstop: map task's uid to parent's
> >  user namespace
> >
> > ptrace_signal: map parent's uid into current's user namespace before
> > including in signal to current.
> 
> Btw, what about the other users of ->si_uid? Say, kill() or tkill().

Well, they end up calling __send_signal().

> Looks like, we need a lot of complications to make this correct...
> 
> As for send_signal(), may be we can simply do
> 
> 
> 	--- x/kernel/signal.c
> 	+++ x/kernel/signal.c
> 	@@ -1084,10 +1084,13 @@ static int __send_signal(int sig, struct
> 				break;
> 			default:
> 				copy_siginfo(&q->info, info);
> 	-			if (from_ancestor_ns)
> 	-				q->info.si_pid = 0;
> 				break;
> 			}
> 	+
> 	+		if (unlikely(from_ancestor_ns)) {
> 	+				q->info.si_pid = 0;
> 	+				q->info.si_uid = 0;
> 	+		}
> 		} else if (!is_si_special(info)) {
> 			if (sig >= SIGRTMIN && info->si_code != SI_USER) {
> 				/*
> 
> ?
> 
> Yes, this "breaks" sys_rt_sigqueueinfo() evem more if it is used
> to send the signal to the sub-namespace.

Eh, yeah, so we do have to use the user_ns_map_uid(), or rather your
new helper.

But you sound more alarmed than that.  So I might be missing something.
You think that user_ns_map_uid() at the locations I identified in
kernel/signal.c does not suffice?

-serge
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