C port scanner

This is a discussion on C port scanner within the Linux Programming forums, part of the Platform Specific Boards category; I want to write simple port scaner in C. Here is my code: Code: #include <stdio.h> #include <unistd.h> #include <sys/types.h> ...

  1. #1
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    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.

  2. #2
    Captain Crash brewbuck's Avatar
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    I don't think we really want to help you make what is essentially a DoS device. Scanning ports has legitimate uses -- blasting packets to the Internet as quickly as possible does not.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  3. #3
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    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.

  4. #4
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by root4 View Post
    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. 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.

    Attempting unauthorized access may be illegal, depending on jurisdiction, and packet-flooding somebody is definitely a DoS and probably illegal. But a law that bans sending any packet of any kind to a host on the Internet is ridiculously draconian, and I don't believe such a law exists (again, depending on your jurisdiction).

    Legality aside, I don't have much interest in helping somebody send packets as quickly as possible to a host, for the purpose of probing that host.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  5. #5
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    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

  6. #6
    Captain Crash brewbuck's Avatar
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    I have a hard time believing a person could be jailed because they sent a single packet to a host. You have to prove intent.

    Blasting a host with packets is clearly a DoS and illegal most places. But attempting to telnet to a port, and getting a rejected connection, is hardly a reason to toss someone in jail.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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