Delphi hook to redirect to different ip

Question

What is the best way to redirect ANY browser to a different ip for specific sites? For example if the user will type www.facebook.com in any browser he will be redirected to 127.0.0.1. Also the same should happen if he will type 66.220.146.11.

What I have until now is this: using the winpkfilter I am able to intercept all the traffic on port 80, with type(in or out), source ip, destination ip and packet. My problem is to modify somehow the packet so the browser will be redirected.

This is the code that i have right now:

program Pass;

{$APPTYPE CONSOLE}

uses
  SysUtils,
  Windows,
  Winsock,
  winpkf,
  iphlp;

var
  iIndex, counter : DWORD;
  hFilt : THANDLE;
  Adapts : TCP_AdapterList;
  AdapterMode : ADAPTER_MODE;
  Buffer, ParsedBuffer : INTERMEDIATE_BUFFER;
  ReadRequest : ETH_REQUEST;
  hEvent : THANDLE;
  hAdapter : THANDLE;
  pEtherHeader : TEtherHeaderPtr;
  pIPHeader : TIPHeaderPtr;
  pTcpHeader : TTCPHeaderPtr;
  pUdpHeader : TUDPHeaderPtr;
  SourceIP, DestIP : TInAddr;

  thePacket : PChar;

  f : TextFile;

  SourceIpString, DestinationIpString : string;
  SourceName, DestinationName : string;

function IPAddrToName(IPAddr : string) : string;
var
  SockAddrIn : TSockAddrIn;
  HostEnt : PHostEnt;
  WSAData : TWSAData;
begin
  WSAStartup($101, WSAData);
  SockAddrIn.sin_addr.s_addr := inet_addr(PChar(IPAddr));
  HostEnt := gethostbyaddr(@SockAddrIn.sin_addr.S_addr, 4, AF_INET);
  if HostEnt <> nil then
    begin
      result := StrPas(Hostent^.h_name)
    end
  else
    begin
      result := '';
    end;
end;

procedure ReleaseInterface();
begin
  // Restore default mode
  AdapterMode.dwFlags := 0;
  AdapterMode.hAdapterHandle := hAdapter;
  SetAdapterMode(hFilt, @AdapterMode);

  // Set NULL event to release previously set event object
  SetPacketEvent(hFilt, hAdapter, 0);

  // Close Event
  if hEvent <> 0 then
    CloseHandle(hEvent);

  // Close driver object
  CloseFilterDriver(hFilt);

  // Release NDISAPI
  FreeNDISAPI();
end;

begin

  // Check the number of parameters
  if ParamCount() < 2 then
    begin
      Writeln('Command line syntax:');
      Writeln('   PassThru.exe index num');
      Writeln('   index - network interface index.');
      Writeln('   num - number or packets to filter');
      Writeln('You can use ListAdapters to determine correct index.');
      Exit;
    end;

  // Initialize NDISAPI
  InitNDISAPI();

  // Create driver object
  hFilt := OpenFilterDriver('NDISRD');

  if IsDriverLoaded(hFilt) then
    begin

      // Get parameters from command line
      iIndex := StrToInt(ParamStr(1));
      counter := StrToInt(ParamStr(2));

      // Set exit procedure
      ExitProcessProc := ReleaseInterface;

      // Get TCP/IP bound interfaces
      GetTcpipBoundAdaptersInfo(hFilt, @Adapts);

      // Check paramer values
      if iIndex > Adapts.m_nAdapterCount then
        begin
          Writeln('There is no network interface with such index on this system.');
          Exit;
        end;

      hAdapter := Adapts.m_nAdapterHandle[iIndex];

      AdapterMode.dwFlags := MSTCP_FLAG_SENT_TUNNEL or MSTCP_FLAG_RECV_TUNNEL;
      AdapterMode.hAdapterHandle := hAdapter;

      // Create notification event
      hEvent := CreateEvent(nil, TRUE, FALSE, nil);

      if hEvent <> 0 then
        if SetPacketEvent(hFilt, hAdapter, hEvent) <> 0 then
          begin
            // Initialize request
            ReadRequest.EthPacket.Buffer := @Buffer;
            ReadRequest.hAdapterHandle := hAdapter;

            SetAdapterMode(hFilt, @AdapterMode);
            counter := 0;
            //while counter <> 0 do
            while true do
              begin
                WaitForSingleObject(hEvent, INFINITE);
                while ReadPacket(hFilt, @ReadRequest) <> 0 do
                  begin
                    //dec(counter);

                    pEtherHeader := TEtherHeaderPtr(@Buffer.m_IBuffer);

                    if ntohs(pEtherHeader.h_proto) = ETH_P_IP then
                      begin
                        pIPHeader := TIPHeaderPtr(Integer(pEtherHeader) +
                          SizeOf(TEtherHeader));
                        SourceIP.S_addr := pIPHeader.SourceIp;
                        DestIP.S_addr := pIPHeader.DestIp;
                        if pIPHeader.Protocol = IPPROTO_TCP then
                          begin
                            pTcpHeader := TTCPHeaderPtr(Integer(pIPHeader) +
                              (pIPHeader.VerLen and $F) * 4);
                            if (pTcpHeader.SourcePort = htons(80)) or
                              (pTcpHeader.DestPort = htons(80)) then
                              begin
                                inc(counter);
                                if Buffer.m_dwDeviceFlags = PACKET_FLAG_ON_SEND
                                  then
                                  Writeln(counter, ') - MSTCP --> Interface')
                                else
                                  Writeln(counter, ') - Interface --> MSTCP');
                                Writeln('     Packet size =    ',
                                  Buffer.m_Length);
                                Writeln(Format('     IP %.3u.%.3u.%.3u.%.3u --> %.3u.%.3u.%.3u.%.3u PROTOCOL: %u',
                                  [byte(SourceIP.S_un_b.s_b1),
                                  byte(SourceIP.S_un_b.s_b2),
                                    byte(SourceIP.S_un_b.s_b3),
                                    byte(SourceIP.S_un_b.s_b4),
                                    byte(DestIP.S_un_b.s_b1),
                                    byte(DestIP.S_un_b.s_b2),
                                    byte(DestIP.S_un_b.s_b3),
                                    byte(DestIP.S_un_b.s_b4),
                                    byte(pIPHeader.Protocol)]
                                    ));
                                Writeln(Format('     TCP SRC PORT: %d DST PORT: %d',
                                  [ntohs(pTcpHeader.SourcePort),
                                  ntohs(pTcpHeader.DestPort)]));

                                //get the data
                                thePacket := pchar(pEtherHeader) +
                                  (sizeof(TEtherHeaderPtr) + pIpHeader.VerLen * 4
                                  + pTcpHeader.Offset * 4);
                                {
                                SourceIpString :=
                                  IntToStr(byte(SourceIP.S_un_b.s_b1)) + '.' +
                                  IntToStr(byte(SourceIP.S_un_b.s_b2)) + '.' +
                                  IntToStr(byte(SourceIP.S_un_b.s_b3)) + '.' +
                                  IntToStr(byte(SourceIP.S_un_b.s_b4));
                                DestinationIpString :=
                                  IntToStr(byte(DestIP.S_un_b.s_b1)) + '.' +
                                  IntToStr(byte(DestIP.S_un_b.s_b2)) + '.' +
                                  IntToStr(byte(DestIP.S_un_b.s_b3)) + '.' +
                                  IntToStr(byte(DestIP.S_un_b.s_b4));
                                }

                              end;
                          end;

                      end;

                    // if ntohs(pEtherHeader.h_proto) = ETH_P_RARP then
                    //   Writeln('     Reverse Addr Res packet');

                    // if ntohs(pEtherHeader.h_proto) = ETH_P_ARP then
                    //   Writeln('     Address Resolution packet');

                    //Writeln('__');

                    if Buffer.m_dwDeviceFlags = PACKET_FLAG_ON_SEND then
                      // Place packet on the network interface
                      SendPacketToAdapter(hFilt, @ReadRequest)
                    else
                      // Indicate packet to MSTCP
                      SendPacketToMstcp(hFilt, @ReadRequest);
                    {
                    if counter = 0 then
                      begin
                        Writeln('Filtering complete');
                        readln;
                        break;
                      end;
                    }
                  end;
                ResetEvent(hEvent);
              end;
          end;
    end;
end.

Answer 1

Use the OS's HOSTS file instead. It is meant for exactly this purpose, and no code is needed.

Answer 2

Since You already know how to read the destination IP from each packet, and you know which IP you want to redirect to, simply store the new IP back to the packet before you pass it to the SendPacketTo...() functions, ie:

if pIPHeader.DestIp = inet_addr('66.220.146.11') then
  pIPHeader.DestIp := inet_addr('127.0.0.1');