Ashwani Wason a écrit :

After debugging a bit into how nf_tproxy_get_sock_v4() looks up a
listener for foreign connections using __inet_lookup_listener() and
compute_score() I found that the problem was happening because of the
way I had the TPROXY rules setup. Those rules work if the proxy has a
single listening socket for INADDR_ANY. If multiple listening sockets
must be used, one for each local address, which is the case for using
SO_BINDTODEVICE then the TPROXY rules must also be "fully qualified"
(with interface name [-i] and IP address thereof [--on-ip]). So the
rules in my example change as follows...

Instead of using:

quoted

iptables -t mangle -A PREROUTING -p tcp --dport 80 -j TPROXY --tproxy-mark 0x1/0x1 --on-port 4002

Use:

iptables -t mangle -A PREROUTING *-i eth0* -p tcp --dport 80 -j TPROXY
--tproxy-mark 0x1/0x1 *--on-ip 192.168.0.65* --on-port 4002
iptables -t mangle -A PREROUTING *-i eth1* -p tcp --dport 80 -j TPROXY
--tproxy-mark 0x1/0x1 *--on-ip 192.168.1.65* --on-port 4002

With these rules the listening socket was looked up correctly and the
sk_bound_dev_if of the socket was honored.

- Ashwani

PS: Sorry to anyone (Jamal) who already spent any time on this.
PPS: Copying the tproxy list in case someone else is looking for this
stuff in the future.

Thanks a lot for sharing your discoveries :)