linux-kernel - Re: RLIMIT_NPROC check in set

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Date:	Wed, 6 Jul 2011 11:01:47 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Slaby <jslaby@...e.cz>, James Morris <jmorris@...ei.org>,
	Neil Brown <neilb@...e.de>, kernel-hardening@...ts.openwall.com
Subject: Re: RLIMIT_NPROC check in set_user()

On Wed, Jul 6, 2011 at 10:36 AM, Vasiliy Kulikov <segoon@...nwall.com> wrote:
> On Sun, Jun 12, 2011 at 17:09 +0400, Vasiliy Kulikov wrote:
>> I'd be happy to hear opinions about improving the fixes above or
>> alternative fixes.
>
> No comments?  Even "Sigh, what a nasty problem.  But we cannot really
> fix it without significantly breaking the stuff.  Go and drink something." ?

Thanks for reminding me.

My reaction is: "let's just remote the crazy check from set_user()
entirely". If somebody has credentials to change users, they damn well
have credentials to override the RLIMIT_NPROC too, and as you say,
failure is likely a bigger security threat than success.

The whole point of RLIMIT_NPROC is to avoid fork-bombs. If we go over
the limit for some other reason that is controlled by the super-user,
who cares?

So let's keep it in kernel/fork.c where we actually create a *new*
process (and where everybody knows exactly what the limit means, and
people who don't check for error cases are just broken). And remove it
from everywhere else.

Hmm?

                     Linus
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