BUG: Unusual TCP Connect() results.

[Alastair Poole <alastair@unixtrix.com>]

I have tested various kernels including 2.6.11.10 2.6.11.11 and 
2.6.12-rc6 and am having unusual results regarding connect().  Earlier 
kernels do not return the same strange results.

I have tested numerous basic port scanners, including my own, and 
strangely ports which are NOT open are being reported as open.  I have 
checked these ports by various means -- to be certain they are NOT open 
-- and in various runlevels; the results are the same.

The number of ports listed changes in size and they appear to be 
random.  For example, on one scan ports 22, 3455, 4532 and 6236 will 
appear open; on another scan it might be 22, 3567, 3879, 3889, 6589 and 
7374. 

However, ports which ARE open do also appear as open alongside these 
"rogue" ports.  I have also tested this on another system with the same 
results.  It is also interesting to note that a basic TCP nmap scan does 
not return these unusual results.

Enclosed is example code that produces these results on the named 
kernels and systems.

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;
}


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