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

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Date:	Tue, 27 Sep 2011 16:38:35 +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 09/27, Serge Hallyn wrote:
>
> Quoting Oleg Nesterov (oleg@...hat.com):
> > On 09/25, Serge E. Hallyn wrote:
> > >
> > > Yes, that's the case I was talking about.  That then proceeds through
> > > send_signal().
> >
> > It doesn't?
>
> No, I was saying it *does*.

But it doesn't ;)

Serge, there is some misunderstanding. And I do not know who is confused,
me or your.

ptrace_signal() simply fills *info with some "random" data before
processing the signal. It doesn't pass this info to send_signal().

If the debuggure wants something meaningfull in *info, it should
fill it itself via PTRACE_SETSIGINFO. This handles the case when
the debugger doesn't really care and only changes signr.

> > +static inline fixup_uid(struct siginfo *info, struct task_struct *t)
> > +{
> > +#ifdef CONFIG_USER_NS
> > +	if (current_user_ns() == task_cred_xxx(t, user_ns)))
> > +#endif
> > +		return;
> > +
> > +	if (SI_FROMKERNEL(info))
> > +		switch (info->si_code & __SI_MASK) {
> > +			default:
> > +				return;
> > +
> > +			case __SI_CHLD:
> > +			case __SI_MESGQ:
> > +				break;
> > +		}
> > +
> > +	info->si_uid = user_ns_map_uid(task_cred_xxx(t, user_ns),
> > +					current_cred(), info->si_uid);
> > +}
> > +
> >  static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
> >  			int group, int from_ancestor_ns)
> >  {
> > @@ -1088,6 +1109,9 @@ static int __send_signal(int sig, struct
> >  				q->info.si_pid = 0;
> >  			break;
> >  		}
> > +
> > +		fixup_uid(info, t);
> > +
> >  	} else if (!is_si_special(info)) {
> >  		if (sig >= SIGRTMIN && info->si_code != SI_USER) {
> >  			/*
>
> It certainly is much simpler.  I'll take some time to walk through all
> of send_signal again and make sure I understand what it does in all
> the cases.

Thanks.



As for ptrace_signal(), it can use the same helper too. Once again,
debugger can use PTRACE_SETSIGINFO, if we really want to fixup si_uid
we should do this even if signr == info->si_signo. OTOH, we do not
know what debugger puts in this chunk of memory. This is like
sigqueueinfo().

Or we can simply leave this code as is. I do not think this si_uid
(in this case) is really important.

Oleg.

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