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Date: Fri, 14 Jan 2011 16:00:55 +0100
From: Bastian Blank <bastian@waldi.eu.org>
To: "Serge E. Hallyn" <serge@hallyn.com>,
        containers@lists.linux-foundation.org,
        kernel list <linux-kernel@vger.kernel.org>,
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        Kees Cook <kees.cook@canonical.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [PATCH 05/08] Allow ptrace from non-init user namespaces
Message-ID: <20110114150055.GA22496@wavehammer.waldi.eu.org>
Mail-Followup-To: Bastian Blank <bastian@waldi.eu.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
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References: <20110111064342.GA27515@mail.hallyn.com>
 <20110111064439.GF27515@mail.hallyn.com>
 <20110114144608.GA20945@wavehammer.waldi.eu.org>
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On Fri, Jan 14, 2011 at 03:46:09PM +0100, Bastian Blank wrote:
> On Tue, Jan 11, 2011 at 06:44:39AM +0000, Serge E. Hallyn wrote:
> > diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> > index 99bbaa3..ec7605d 100644
> > --- a/kernel/ptrace.c
> > +++ b/kernel/ptrace.c
> > @@ -134,21 +134,24 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
> >  		return 0;
> >  	rcu_read_lock();
> >  	tcred = __task_cred(task);
> > -	if ((cred->uid != tcred->euid ||
> > -	     cred->uid != tcred->suid ||
> > -	     cred->uid != tcred->uid  ||
> > -	     cred->gid != tcred->egid ||
> > -	     cred->gid != tcred->sgid ||
> > -	     cred->gid != tcred->gid) &&
> > -	    !capable(CAP_SYS_PTRACE)) {
> > -		rcu_read_unlock();
> > -		return -EPERM;
> > -	}
> > +	if (cred->user->user_ns == tcred->user->user_ns &&
> > +	    (cred->uid == tcred->euid &&
> > +	     cred->uid == tcred->suid &&
> > +	     cred->uid == tcred->uid  &&
> > +	     cred->gid == tcred->egid &&
> > +	     cred->gid == tcred->sgid &&
> > +	     cred->gid == tcred->gid))
> > +		goto ok;
> > +	if (ns_capable(tcred->user->user_ns, CAP_SYS_PTRACE))
> > +		goto ok;
> > +	rcu_read_unlock();
> > +	return -EPERM;
> > +ok:
> 
> This is wrong.

Whoops, it _is_ right. However the nested parenthes is unnecessary and
can lead to other conclusions.

Bastian

-- 
Lots of people drink from the wrong bottle sometimes.
		-- Edith Keeler, "The City on the Edge of Forever",
		   stardate unknown