From: Baptiste Jonglez <baptiste@bitsofnetworks.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: WireGuard mailing list <wireguard@lists.zx2c4.com>
Subject: Varying source address and stateful firewalls (Was: Multiple Endpoints)
Date: Mon, 9 Jan 2017 12:35:44 +0100 [thread overview]
Message-ID: <20170109113544.GB4526@lud.polynome.dn42> (raw)
In-Reply-To: <CAHmME9pSJ3gsAUdNhk_Lt-QzOf6+eS=cay_Chq8YpdcaZJbCsA@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 2185 bytes --]
On Mon, Jan 09, 2017 at 12:00:17AM +0100, Jason A. Donenfeld wrote:
> > I merely pointed out that a stateful firewall is similar to a symmetric
> > NAT, that is, both would cause issue with peer roaming.
>
> Are you sure about this for UDP? I did a bunch of tests several months
> ago, and was able to punch holes in a variety of stateful firewalls
> with changing remote IPs.
I must admit I had never tested :)
I just did, though, and yes, the stateful firewall from Linux does block
UDP traffic from unrelated source IP addresses. So I guess your hole
punching was based on some other property.
Here is the setup with 3 computers A, B, C. There is a stateful firewall
on A, and A opens a UDP connection towards B. C then tries to pretend to
be B and contacts A with the same src/dest port.
A# iptables -F INPUT
A# iptables -A INPUT -p udp -m conntrack --ctstate ESTABLISHED -j LOG --log-prefix="established: "
A# iptables -A INPUT -p udp -m conntrack --ctstate RELATED -j LOG --log-prefix="related: "
A# iptables -A INPUT -p udp -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
A# iptables -A INPUT -p udp -j LOG --log-prefix="drop: "
A# iptables -A INPUT -p udp -j DROP
A and B communicate normally:
B# nc -l -u -p 5001
A# nc -u -p 60000 $IP_B 5001
A# #type something
B# #type something else
At this point, there is an entry in the conntrack table of A:
A# conntrack -L | grep $IP_B
udp 17 22 src=$IP_A dst=$IP_B sport=60000 dport=5001 src=$IP_B dst=$IP_A sport=5001 dport=60000 mark=0 use=1
Also, the packet from B to A has been logged by our firewall rules:
kernel: established: IN=wlan0 OUT= SRC=$IP_B DST=$IP_A LEN=33 TOS=0x00 PREC=0x00 TTL=62 ID=43432 DF PROTO=UDP SPT=5001 DPT=60000 LEN=13
Now C tries to chime in, contacting A and pretending to be B:
C# nc -u -p 5001 $IP_A 60000
The result:
kernel: drop: IN=wlan0 OUT= SRC=$IP_C DST=$IP_A LEN=34 TOS=0x00 PREC=0x00 TTL=64 ID=43124 DF PROTO=UDP SPT=5001 DPT=60000 LEN=14
So, the packet from C is dropped, even though it has the same source port
and destination port as the ones from B.
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
next prev parent reply other threads:[~2017-01-09 11:26 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-07 14:43 Multiple Endpoints em12345
2017-01-07 15:23 ` Jason A. Donenfeld
2017-01-07 16:45 ` em12345
2017-01-08 14:12 ` Baptiste Jonglez
2017-01-08 14:39 ` Jörg Thalheim
2017-01-08 21:22 ` Baptiste Jonglez
2017-01-08 22:19 ` Jason A. Donenfeld
2017-01-08 22:18 ` Jason A. Donenfeld
2017-01-08 22:57 ` Baptiste Jonglez
2017-01-08 23:00 ` Jason A. Donenfeld
2017-01-09 11:35 ` Baptiste Jonglez [this message]
2017-01-10 4:32 ` Varying source address and stateful firewalls (Was: Multiple Endpoints) Jason A. Donenfeld
2017-01-15 10:01 ` Multiple Endpoints Jason A. Donenfeld
2017-01-08 22:14 ` Jason A. Donenfeld
2017-01-10 0:33 Varying source address and stateful firewalls (Was: Multiple Endpoints) em12345
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170109113544.GB4526@lud.polynome.dn42 \
--to=baptiste@bitsofnetworks.org \
--cc=Jason@zx2c4.com \
--cc=wireguard@lists.zx2c4.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).