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

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Message-ID: <m1d3p0qhl5.fsf@fess.ebiederm.org>
Date:	Fri, 17 Dec 2010 12:17:58 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	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

"Serge E. Hallyn" <serge@...lyn.com> writes:

> 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?

I mean cred and tcred are only use in kill_ok_by_cred.
So we can eliminate those two variables from check_kill_permission.

>> >  	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);


Eric
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