netdev - Re: [BUG] SNAT sometimes allows packets to pass through unchanged

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <499C3E34.7080405@trash.net>
Date:	Wed, 18 Feb 2009 17:58:28 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	netdev@...r.kernel.org,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] SNAT sometimes allows packets to pass through unchanged

Alan Stern wrote:
> On Mon, 16 Feb 2009, Patrick McHardy wrote:
> 
>> The NAT table only sees the first packet of every connection
>> and never INVALID packets. The mangle table should work fine.
> 
> I ended up adding a rule to the FORWARD chain of the filter table.  
> The trick was to select based on the state.  That worked; it saw all
> those un-NATed packets and was able to eliminate them.  In case you're
> curious, the rule was essentially this:
> 
> iptables -A FORWARD -o eth1 -s 10.0.0.0/8 -m state --state INVALID -j DROP
 >
> Ideally, the rule should select all the packets which haven't been
> altered by SNAT, not just the ones marked INVALID.  Is there any way to
> do this?

Not in the sense that you could somehow catch valid packets "missed"
by SNAT, that would be a bug. The conntrack match supports matching
on whether the state says that a packet should be NATed.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html