[tproxy] TProxy implementation.

[강기호]

Hello.

I'm trying to make transparent proxy for controlling HTTP access to web-
server. 
All was implemented in Kernel 2.4.19.
So, I used on kernel's instead user-mode functions, tcp_setsockopt for
setsockopt, sk for sock, memcpy for copy_from/to_user.

Before sk->prot->connect(=tcp_v4_connect) to server setted tproxy like
below :

memset(itp, 0x00, sizeof(struct in_tproxy));
memcpy(&(itp->itp_faddr.s_addr), &(client->sk->daddr), sizeof(struct
in_addr));
itp->itp_fport = 0;
memcpy(&(server->sk->rcv_saddr), &(client->sk->saddr), sizeof(struct
in_addr));

tperr = sk->prot->setsockopt(sk, SOL_IP, IP_TPROXY_ASSIGN, (char *)itp,
sizeof(struct in_tproxy));
flags = ITP_CONNECT;
tperr = sk->prot->setsockopt(sk, SOL_IP, IP_TPROXY_FLAGS, (char *)&flags,
sizeof(int));


And after tcp_close, unsetted tproxy like below :

tperr = sk->prot->setsockopt(sk, SOL_IP, IP_TPROXY_UNASSIGN, NULL, 0);


And configured iptable :

iptables -t nat -A PREROUTING -p tcp -d 10.1.1.10 --dport 80 -j REDIRECT --
to-port 80


I configured my transparent proxy box(has 1 network interface card) with
Layer-4 switch(for Cache-Redirect).
Just started, Tproxy working fine.
Few minutes later, Tproxy send packet with other's foreign address to
destination host irregularly.
But client received response exactly.
When that appeared, my reverse proxy box has 4000 established TCP server
connections and hash table size was same.

I don't know why that happen.
Am I missed or wrong?
Thanks.