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Do you also properly adjust DNS records length? (See dnsr_rdlength in the dns_record structure on the following link http://www.chiark.greenend.org.uk/ucgi/~richardk/cvsweb/dns/dns.h?rev=1.8&content-type=text/x-cvsweb-markup)
When I ‘overwrite’ the dns packet, can I do this within the already allocated buffer (by winpkfilter) OR do I need to create a totally new buffer. If so I do not have a clue how …. do you have an example ?
You can do this in the already allocated buffer. Actually, packet buffer is allocated by you, passed to WinpkFilter, which copies packet data into it and returns buffer to you. You can do anything with the packet but don’t forget to adjust packet length and recalculate requred checksums (UDP and IP in case of DNS).
As for the sample, Internet Gateway makes DNS redirect, it may help a bit. However, it does not modify DNS data, only packet header.
In case of DNS hijacking the easiest way is changing IP in the DSN response packet. You are right here.
In case of DNS you can form a new packet and replace the original one with it. It’s pretty easy to do because DNS works over UDP. However, the same trick with TCP packet is much more complex. Packets in TCP stream has sequence and aknowledgement numbers which are incremented to the amount of data payload in the packet. So if you change data length you must also track changes in SEQ and ACK fileds.
Well, yes it looks that Sygate is a problem. Their NDIS driver makes a dirty hook by modifying TCPIP.SYS module image (ArpSend routine if I remember fine). The only possible work around I could find is re-patching TCPIP.SYS after Sygate driver, but I really don’t like this solution. You can try to explain Sygate that dirty hacking is no good but I don’t think they would listen.
Latest WinpkFilter release also includes NDIS IM variant of WinpkFilter driver. Basically it was created to be used for Windows x64 (patching system is hardly possible there unless patching KeBugCheckEx in the kernel or something of this kind, see the notes from MS here http://www.microsoft.com/whdc/driver/kernel/64bitPatching.mspx). However, you can also use this driver for the latest operating systems (Windows 2000/XP/2003). By design it can coexists with Sygate driver, so it’s also a variant.
Internet Gateway 1.0 released. This is the first sample (even more than sample, it can be successfully used in the real environment) from the Advanced WinpkFilter Samples series which is targeted to demonstrate WInpkFilter libraries applicability. The source code for Internet Gateway is available to all registered WinpkFilter customers.
WinpkFilter 3.0.1 released. This service release includes:
1. Few improvements/bugfixes in legacy Windows 9x/ME driver.
2. Slightly changed driver API structures. Please refer WinpkFilter online documentation for the details.
3. All sample applications and API DLL now include Visual Studio 2005 projects. This greatly simplifies development under Windows XP/2003 x64.If you are eligible for a free update, please send the following details to [email protected] to receive an update instruction:
1. Your order ID.
2. An approximate date of purchasing.Determine all connections for the application (with LHMON) and limit bandwidth for these connections. Usually bandwidth limit is realized using packets queue and timer. An example, timer triggeres each 100 ms, in the timer routine you calculate how many ms passed since last timer (Windows is not RTOS) and calculate how many bytes you can process from the application associated packets queue. After this you should process as many packets from the queue as covered by these bytes.
Hope it helps…
In general it’s hardly possible to create common rules, because these rules should contain your (or/and remote system IP’s). However, for the Internet user (not a server system) usually it’s more than enough to use one of the Stealth modes without setting any additional rules.
In case of proxy packet directed to IPproxy (where IPproxy is the proxy IP address). You still can redirect packets from IPproxy to your IP (I assume you fully control this system) and process it by your own proxy.
Another possible approach is parsing/modification of HTTP(DNS) packets payload but it’s a bit more complicated.
Sorry, but using hostname for the rule is not possible (actually it would be potentionally dangerous security hole). Making a work around depends from your configuration and security requirements so it is a bit difficult to advise.
Lets assume that you want to redirect user from IP1 to IP2. In order to do so you must do the following:
1) For the outgoing packet change destination IP from IP1 to IP2 and recalcuilate IP checksum. Save the connection state (IP’s, TCP ports).
2) For the incoming packet check if it is from IP2 and if yes also check port information (to be sure that this packet is associated with redirected connection). After this substitute source IP from IP2 to IP1 and recalculate IP checksum.
3) And so on… For the outgoing packets use 1) and use 2) for incoming.
WinpkFilter 3.0 released. This release introduces Windows XP x64 and Windows Server 2003 x64 support. Also includes few bugfixes and API extensions. Please refer WinpkFilter online documentation for the details. If you are eligible for a free update, please send the following details to [email protected] to receive an update instruction:
1) Your order ID.
2) An approximate date of purchasing.
Besides DeviceRawIp, is there any other way to inject a raw IP packet to TCP/IP protocol stack? Seems NDIS Intermediate Driver not usable, because the raw IP packet needs to be routed.
You can inject packet using NDIS IM or NDIS hook driver (up to the stack or down to the network interface) but you must know exactly what you are doing (to choose correct network interface and packet indication).
DeviceIp can’t be used for sending custom packets, in general it is used for managing TCP/IP protocol stack, not for communication (however, there is an IOCTL used for sending ICMP PING). However, I think you can use deviceRawIp. I have never tried it myself but I suppose it provides TDI transport interface for sending/receiving raw IP packets.
Other ideas look OK.
