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

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Date:	Tue, 20 Sep 2011 18:24:55 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Serge Hallyn <serge.hallyn@...onical.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

On 09/20, Serge Hallyn wrote:
>
> Quoting Oleg Nesterov (oleg@...hat.com):
> >
> > As for __send_signal() in particular, I guess we could do
> >
> > 		q->info.si_uid = from_ancestor_ns ? 0 : current_uid();
>
> But wait - can't __send_signal end up being triggered through fcntl
> F_SETSIG+F_SETOWN to another but none-ancestor namespace?

I didn't really check, but afaics send_sigio_to_task/etc never use
SEND_SIG_NOINFO. And they shouldn't, there is no the sending process.

> do actually need to call the full user_ns_map_uid() there.  However,
> the uid sent in ptrace_signal() can (if i'm thinking right) be set
> using
>
> 	info->si_uid = (current_user_ns() == parent_user_ns()) ?
> 			0 : current_uid();
>
> Not much of a win performance-wise, but perhaps better by making it
> clear that those are the only possibilities (and overflowuid is not
> possible).

I think you are right right, except s/==/!=/. This is like send_signal()
which can only send the signal down or to the same namespace.

I guess ptrace_signal() can even do

	info->si_pid = task_pid_vnr(current->parent);

	if (info->si_pid)	// same namespace
		info->si_uid = current_uid();
	else			// can't see the tracer, we are from the sub-namespace
		info->si_uid = 0;

Whatever you like more.

And just in case let me repeat, I won't argue if you use
user_ns_map_uid/helper for consistency. Without CONFIG_USER_NS it is
even better performance-wise (even if we add a helper I guess).

So this all is up to you.

Oleg.

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