[strongSwan-dev] xfrm by MARK: tcp problems when mark for in and out differ
Gerd v. Egidy
lists at egidy.de
Wed Oct 13 15:57:06 CEST 2010
Hi,
I use current strongswan git to set up ipsec connections with the xfrm by MARK
feature. When I configure xfrm policies with different marks for incoming and
outgoing packets, incoming tcp connections can't be established anymore. The
SYN-ACK packet is never sent through the tunnel.
An example policy looks like this:
src 192.168.5.0/24 dst 192.168.1.0/24
dir out priority 1760
mark 5/0xffffffff
tmpl src 172.16.1.131 dst 172.16.1.130
proto esp reqid 16384 mode tunnel
src 192.168.1.0/24 dst 192.168.5.0/24
dir fwd priority 1760
tmpl src 172.16.1.130 dst 172.16.1.131
proto esp reqid 16384 mode tunnel
src 192.168.1.0/24 dst 192.168.5.0/24
dir in priority 1760
tmpl src 172.16.1.130 dst 172.16.1.131
proto esp reqid 16384 mode tunnel
-> incoming packets are without mark, outgoing packets are marked with 5
I traced the packet in the xfrm code and found out that the problem is in the
flow data. When the SYN-ACK hits __xfrm_lookup, the value in fl->mark is 0
(more precisely: the mark value used in the incoming packet). This means that
xfrm_policy_match will not match on the correct policy because the mark values
differ.
I'm not too familiar with the kernel networking code. But I guess that the
flow for the SYN-ACK is set up based on the data used for the SYN and is not
updated when my iptables rule changes the mark of the packet:
iptables -t raw -A OUTPUT -s 192.168.5.0/255.255.255.0 -d
192.168.1.0/255.255.255.0 -j MARK --set-mark 5
I guess that the flow data should be updated somewhere. But I don't know what
the correct place for that code would be.
Can somebody more familiar with the network stack help me with this please?
Thank you very much.
Kind regards,
Gerd
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