From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pablo Neira Ayuso Subject: Re: "Late REDIRECT" Date: Mon, 13 Mar 2006 12:01:10 +0100 Message-ID: <441550F6.7060609@eurodev.net> References: <44153615.50408@netboxblue.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Netfilter Development Mailinglist Return-path: To: Menno Smits In-Reply-To: <44153615.50408@netboxblue.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: netfilter-devel-bounces@lists.netfilter.org Errors-To: netfilter-devel-bounces@lists.netfilter.org List-Id: netfilter-devel.vger.kernel.org Menno Smits wrote: > Hi, > > Just wanted to ask for your opinions on an idea. Please let me know if > you think this is too difficult or crazy. > > We use currently use the REDIRECT target in nat PREROUTING to send > specific traffic to proxies running on our gateway (http, pop3, dns and > smtp). > > This works ok but we have the following problems: > > 1) nat PREROUTING happens before filter FORWARD. If we want to apply > consistent filter rules to outbound traffic regardless of whether it > goes via a transparent proxy or directly out then we can't because the > transproxied traffic never goes thru filter FORWARD. Currently we use a > horrible system of marks set in mangle PREROUTING to work around this. > We reject packets in FORWARD or skip the REDIRECTs in nat based on the > marks set. This is ugly and hard to debug (esp because we also use marks > for traffic shaping). > > 2) Return traffic from the transparent proxy REDIRECTs has the source IP > and source port of the transparent proxy listener, not the true remote > site and port. This means that when we do accounting for return traffic > (using ULOG in mangle POSTROUTING) the remote host and port are incorrect. > > A possible solution to the above problems is to allow REDIRECTs to occur > in nat POSTROUTING (a "late redirect" for want of a better term). That > way all outbound traffic can pass through filter FORWARD before being > REDIRECTed. The reply NAT for the late REDIRECT would work in a similar > way, being performed before filter FORWARD so that the true source IP > and port is seen there. > > Is something like this feasible? How difficult would it be implement? Am > I barking up the wrong tree? Ick, this seems frigthening. Why don't you filter in the raw PREROUTING? -- Pablo