StrongTCP

A small program which will modify every packet from --queue num whose pkg_data_len >= 0, or DROP it otherwise.

As an immediate consequence, all RST packets are DROPped, which is favored in most situations.

To achieve that (on Linux) you will need the following

#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <linux/netfilter.h>            /* for NF_ACCEPT */
#include <libnetfilter_queue/libnetfilter_queue.h>

For those impatient

if (pkg_data_len >= 0)
{
  blah(&manythings);

  //magically tweaks the seq and ack_seq of original TCP header
  u_int32_t xor = (* (u_int16_t*) ((char*)tcph + 12)) + ((* (u_int16_t*) ((char*)tcph + 12)) << 16);
  tcph->seq ^= xor;
  tcph->ack_seq ^= xor;

  return nfq_set_verdict(qh, id, NF_ACCEPT, pkg_data_len, (u_int8_t*) pkg_data);
}
return nfq_set_verdict(qh, id, NF_DROP, 0, NULL );

Build

• Linux

cd src
make

• Openwrt

make menuconfig
make

• Android

ndk-build

About the author, of this README

• Nobody is going to understand WTF does these code do without a README.md, so I wrote one
• No copyright information provided

Disclaimer

• removed according to regulation.