From owner-freebsd-hackers Wed Dec 19 8:51: 5 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from comp.chem.msu.su (comp-xl.chem.msu.su [158.250.32.157]) by hub.freebsd.org (Postfix) with ESMTP id 0078337B417; Wed, 19 Dec 2001 08:50:51 -0800 (PST) Received: (from yar@localhost) by comp.chem.msu.su (8.11.1/8.11.1) id fBJGomF32005; Wed, 19 Dec 2001 19:50:48 +0300 (MSK) (envelope-from yar) Date: Wed, 19 Dec 2001 19:50:48 +0300 From: Yar Tikhiy To: Ruslan Ermilov Cc: net@FreeBSD.ORG, hackers@FreeBSD.ORG Subject: Re: Processing IP options reveals IPSTEALH router Message-ID: <20011219195047.E21732@comp.chem.msu.su> References: <20011219181929.A20425@comp.chem.msu.su> <20011219173313.C54315@sunbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20011219173313.C54315@sunbay.com>; from ru@FreeBSD.ORG on Wed, Dec 19, 2001 at 05:33:13PM +0200 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Wed, Dec 19, 2001 at 05:33:13PM +0200, Ruslan Ermilov wrote: > On Wed, Dec 19, 2001 at 06:19:29PM +0300, Yar Tikhiy wrote: > > > > I ran into an absolutely clear, but year-old PR pointing out that > > a router in the IPSTEALTH mode will reveal itself when processing > > IP options: kern/23123. > > > > The fix proposed seems clean and right to me: don't do IP options > > at all when in the IPSTEALTH mode. Does anyone have objections? > > If no, I'll commit the fix. > > > What if the packet is directed to us? I think we should still > process options in this case, and the patch in the PR doesn't > seem to do it. Good point! Indeed, just ignoring IP options would let a third party to identify a FreeBSD host as a stealthy router. I think it's safe to move doing IP options to after identifying an IP packet as destined for this or another host. I'll make a patch and show it here. > > I was going to replace IPSTEALTH functionality with the > net.inet.ip.decttl knob. Setting it to 0 would match the > IPSTEALTH behavior, the default value will be 1. > In fact, IPSTEALTH does already have a sysctl knob: net.inet.ip.stealth, which is initially zero (i.e. don't be stealthy.) To my mind, the "stealth" name fits its purpose better since just leaving TTL untouched is insufficient for a router to achieve really stealthy behaviour. -- Yar To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message