addrule.c

Linux下kernel与userspace的通信实现。主要功能为可修改linux的防火墙设置进行通信控制。Linux下调试通过。

#define _GNU_SOURCE
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <netdb.h>
#include <string.h>
#include <firewall.h>
#include <errno.h>



/* converts valid IP-Address string into IP-address in suitable format for kernel */
IPAddressByteType convertIPAddress (char *IPAddressString, int *error) {

  *error = 0; 
  struct hostent *IPAddress; 
  IPAddressByteType IPAddressByte;

  IPAddress = gethostbyname (IPAddressString);
  if (!IPAddress) {
    *error = h_errno;
    return 0;
  }

  if (IPAddress->h_length != sizeof (IPAddressByteType)) {
    fprintf (stderr, "Wrong code!\n");
    exit (1);
  }
  memcpy((char *)&IPAddressByte, (char *)IPAddress->h_addr, 
	IPAddress->h_length);
  
  return IPAddressByte;
}


int main (int argc, char **argv) {
  
  IPAddressByteType IPAddress;
  int error;
  FILE *procFile;
  ssize_t noWritten;
  int bufferLength;
  int tmp;

  bufferLength = 2*sizeof (int) + strlen (argv[2]) + 1  + sizeof (IPAddressByteType);
  
  char buffer[bufferLength];

  if (argc != 5) {
    fprintf (stderr, "Exactly four arguments required!\n");
    exit (1);
  }
 
  procFile = fopen (argv[1], "w"); 
  
  if (!procFile) {
    fprintf (stderr, "Opening failed!\n");
    exit (1);
  }

  /* convert the IP-address into format suitable for kernel */
  IPAddress = convertIPAddress (argv[3], &error);
  if (error) {
    fprintf (stderr, "Converision of IP-address failed \n");
  }

  /* copy the port number into the buffer */
  tmp = atoi (argv[4]);
  memcpy (buffer, &tmp, sizeof (int));

  /* copy the length of the program string into the buffer */
  tmp = strlen (argv[2]) + 1;
  memcpy (buffer + sizeof (int), &tmp, sizeof (int));

  /* copy the program string into the buffer */
  strncpy (buffer +2 * sizeof (int), argv[2], strlen (argv[2]) + 1);

  /* copy the IP-address into the buffer */
  memcpy (buffer + 2 *sizeof (int) + strlen (argv[2]) + 1, &IPAddress, sizeof (IPAddressByteType));

  /* write the buffer to the kernel */
  noWritten = fwrite (buffer, 1, bufferLength, procFile);
  if (noWritten != bufferLength) {
    perror ("Couldn't write data!\n");
  }
  fclose (procFile);
  
  exit (0);

}