Re: BUG: Unusual TCP Connect() results.

[Alastair Poole <alastair@unixtrix.com>]

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Michal Schmidt wrote:

>>> What is the last version that works as expected for you?
>>
Kernel 2.6.11, though I can't check others due to bandwidth 
restrictions.  2.6.11.10 through 2.6.12-rc6 all have the same issue.

>>> Are you testing your scanner only on localhost? Maybe you are just 
>>> lucky and connect your TCP socket to itself.
>>
This problem only occurs on localhost.  I don't think it is mere luck, 
these are too frequent and strange for this.

>>>
>>> What are these asterisks doing there? Next time when you copy&paste 
>>> code, please make sure you don't mangle it.
>>>
I apologise for this, included this time is an attatchment in the hope 
you are able to reproduce the strange results I and others have been 
able to.  Try testing multiple times, I find that 18 out of 20 runs 
produces the same type of results.

sincerely

Alastair Poole

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

int
main (int argc, char **argv)
{
 int sd, result, server_port;
 struct hostent *he;
 struct sockaddr_in servaddr;

 printf ("Test TCP/IP port scanner:\n");

 if (argc != 2)
   {
     printf ("Usage: %s host\n", argv[0]);
     exit (1);
   }

 if ((he = gethostbyname (argv[1])) == NULL)
   {
     perror ("gethostbyname()");
     exit (1);
   }

 printf ("Scanning %s\n", argv[1]);

 for (server_port = 0; server_port < 65536; server_port++)
   {
     if ((sd = socket (PF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1)
    {
      perror ("socket()");
      exit (1);
    }

     bzero (&servaddr, sizeof servaddr);
     servaddr.sin_family = AF_INET;
     servaddr.sin_port = htons (server_port);
     servaddr.sin_addr = *((struct in_addr *) he->h_addr);

     result = connect (sd, (struct sockaddr *) &servaddr, sizeof servaddr);

     if (result != -1)
    {
      printf ("open port:  %d\n",server_port);
    }
     close (sd);
   }
 return result;
}