Thread: C port scanner

I want to write simple port scaner in C. Here is my code:

Code:

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {

struct hostent *host;
struct sockaddr_in addr;
int PortSocket;
int from_port = atoi(argv[2]);
int to_port = atoi(argv[3]);


if((host = gethostbyname((const char*)argv[1])) == NULL) {
        puts("Bad address\n");
        _exit(-1);
}
int i = 0;
for(i = from_port; i <= to_port; i++) {
if((PortSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1) {
        puts("Can not create socket\n");
        _exit(-1);
}

addr.sin_family = AF_INET;
memcpy(&(addr.sin_addr), host->h_addr, host->h_length);
addr.sin_port = htons(i);

        if(connect(PortSocket, (struct sockaddr *)&addr, sizeof(addr)) == -1)continue;
        printf("Port %d open\n", i);
close(PortSocket);
        }
return 0;
}

On LAN working it Ok. But if I try to scan some address from internet it take much more time, for connecting to the ports. I have quite fast connection to the internet. How to set time limit for connect function?.. or if you have some other solution.
Thnak you.

Port scanning (outside of your lan) is illegal, check your ISP policy for details. Concerning the purely technical question about tcp timeouts, they are configurable via the kernel pseudo-fs /proc/sys/net.

Sending packets on the Internet is not illegal.

Really? ...

The security of a host does not depend on whether a person is legally allowed to probe it. Depending on such a thing would be idiotic.

Who said the security of a host was depending on the ability to probe it? I was just saying that port scanning (as DoS method) is illegal -- but ok, that's not /illegal/ (at least not directly), simply against most ISP policy -- my bad. However it can go further than a simple 'ban' (see the link below)...

Check this page for details: http://nmap.org/book/legal-issues.html