linux-kernel - Re: [RFC 4/5] user namespaces: allow killing tasks in your own or child userns

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Date:	Fri, 17 Dec 2010 20:09:03 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	LSM <linux-security-module@...r.kernel.org>,
	James Morris <jmorris@...ei.org>,
	Kees Cook <kees.cook@...onical.com>,
	containers@...ts.linux-foundation.org,
	kernel list <linux-kernel@...r.kernel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Michael Kerrisk <michael.kerrisk@...il.com>
Subject: Re: [RFC 4/5] user namespaces: allow killing tasks in your own or
 child userns

Quoting Eric W. Biederman (ebiederm@...ssion.com):
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -659,11 +686,7 @@ static int check_kill_permission(int sig, struct siginfo *info,
> >  	cred = current_cred();
> >  	tcred = __task_cred(t);
> Nit pick  you don't need to compute cred and tcred here now.

Just to make sure I understand right: you mean wait until after the
same_thread_group() check to save calculation in that case, right?

> >  	if (!same_thread_group(current, t) &&
> > -	    (cred->euid ^ tcred->suid) &&
> > -	    (cred->euid ^ tcred->uid) &&
> > -	    (cred->uid  ^ tcred->suid) &&
> > -	    (cred->uid  ^ tcred->uid) &&
> > -	    !capable(CAP_KILL)) {
> > +	    !kill_ok_by_cred(t)) {
> >  		switch (sig) {
> >  		case SIGCONT:
> >  			sid = task_session(t);
--
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