Date: Fri, 17 Dec 2010 20:09:03 +0000
From: "Serge E. Hallyn" <serge@hallyn.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
        LSM <linux-security-module@vger.kernel.org>,
        James Morris <jmorris@namei.org>, Kees Cook <kees.cook@canonical.com>,
        containers@lists.linux-foundation.org,
        kernel list <linux-kernel@vger.kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Michael Kerrisk <michael.kerrisk@gmail.com>
Subject: Re: [RFC 4/5] user namespaces: allow killing tasks in your own or
 child userns
Message-ID: <20101217200903.GA15528@mail.hallyn.com>
References: <20101217152246.GA8221@mail.hallyn.com>
 <20101217152458.GA11162@mail.hallyn.com>
 <20101217152547.GB11162@mail.hallyn.com>
 <20101217152625.GC11162@mail.hallyn.com>
 <20101217152659.GD11162@mail.hallyn.com>
 <m14oacryar.fsf@fess.ebiederm.org>
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Quoting Eric W. Biederman (ebiederm@xmission.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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