File greylist.c of Package qmail-spp-plugins

/*
* Copyright (C) 2007 Sebastian Werner <blackwing@blackwing.de> 
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later
* version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
*/

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

#define BASEDIR         "/var/qmail/greylist"
#define	ENV_BASEDIR	"GL_BASEDIR"

#define	ENV_MIN_REJECT	"GL_MIN_REJECT"
#define ENV_MAX_WAIT	"GL_MAX_WAIT"
#define ENV_ACCEPT_GOOD	"GL_ACCEPT_GOOD"

// Initial waiting time 5min
#define DEFAULT_MIN_REJECT	300
// Wait one day after first seen, before forgetting
#define DEFAULT_MAX_WAIT	86400
// Entries stay valid for 32 days
#define DEFAULT_ACCEPT_GOOD	2764800

int ppid;
time_t now;
int  min_reject, max_wait, accept_good;
/*
* Basic ideas of this pretty "flat" implementation:
* - Create a file per remote IP address when host is seen for first time
* - Issue a 451 error as long as minimum waiting time is not met
* - When host comes back after minimum waiting time, update the files atime
*   to the current time and accept the mail
* - If after first seen the host did not come back until max waiting time 
*   is hit, delete the entry 
* - After a lifetime of "accept_good" delete the entry of the file as well
*
* So per host we get _one_ file.
* The mtime of this file is the time, this host has been seen the first time.
* Its atime is corresponding time, when this host has been seen the last time.
* 
* I choosed the one-file-per-host model, because it is easy to maintain.
* For high-volume mail servers, it is advisable to put the basedir on a
* ramdisk with little size but many inodes :)
*
* Actually this concept is also IPv6 safe.
*
* Please send patches & suggestions to blackwing@blackwing.de
*/

/***********************************************************************************/

/* remove the entry of a hostname by unlinking the corresponding file */
int
remove_ip (char* host)
{
  if(unlink(host) < 0)
    {
      fprintf (stderr,
             "greylist: pid %d - removing stale entry %s failed: %s\n",
             ppid,host,strerror(errno));
      return(-1);
    }

return(1);
}

/* check wether in basedir a valid entry for the corresponding host is to be found */
int
check_ip (char* host)
{
  struct stat hostfile;
  int retval;
  
  // file does not exist - so never seen before
  if ( stat ( host, &hostfile ) < 0 )
    {
      return(-1); 
    }
    
  // user is back too soon
  if (now - hostfile.st_mtime < min_reject)
    {
      return(0);
    }

// host was not back soon enough after first try. unlink the entry.
  if ((now - hostfile.st_atime > max_wait) && (hostfile.st_atime == hostfile.st_mtime))
    {
      retval = remove_ip(host);
      return(-2);
   }
  
     
  // max lifetime of the entry is reach. unlink the entry.
  if (now - hostfile.st_atime > accept_good)
    {
      retval = remove_ip(host);
      return(-3);
    }

// host has met requirements.
  return(1);
}

/* create a file based on the hostname */
int
add_ip (char* host)
{
  int file = open(host, O_CREAT | O_RDWR | O_NOFOLLOW, S_IRUSR | S_IWUSR);
 
  if (file < 0)
    { 
      fprintf (stderr,
             "greylist: pid %d - creating %s failed: %s\n",
             ppid,host,strerror(errno));
      return(-1);
    }

close(file);
  return(1);
}

/* update the atime of the file for the specified hostname */
int
update_ip (char* host)
{
  
  struct utimbuf newutime;
  struct stat hostfile;
  
  if ( stat ( host, &hostfile ) < 0 )
    {
	/* This should never happen! */
      return(-1); 
    }

// assign new last-seen time
  newutime.actime = now;
  newutime.modtime = hostfile.st_mtime;
 
  if ( utime ( host, &newutime ) < 0 )
    {
      fprintf (stderr,
             "greylist: pid %d - updating %s failed: %s\n",
             ppid,host,strerror(errno));
      return(-1);
    }

return(1);  
}

/* parse an numeric environment variable */
int 
get_numeric_option (char *name, int dflt) {
  char *value = getenv(name);

if (value)
    {
      return atoi(value);
    }
  return dflt;
}

int
main (int argc, char *argv[])
{
  char *addr = getenv ("TCPREMOTEIP");
  ppid = getppid ();
  now = time(NULL);

/* Are we running in an tcpserver environment? */
  if (!addr)
    {
      printf ("D\n");
      fprintf (stderr,
              "greylist: pid %d - no TCPREMOTEIP\n",
              ppid);
      exit (0);
    }

/* User disabled plugin via tcp.smtp - so exit */
  if (getenv ("SKIP_GREY"))
    {
      fprintf (stderr,
               "greylist: pid %d - greylisting skipped.\n",
               ppid);
      exit (0);
    }

/* Change to basedir, where all the files are */
  char* basedir = getenv(ENV_BASEDIR);
  if (!basedir)
    basedir = BASEDIR;
  
  if (chdir(basedir) < 0)
    {
      fprintf (stderr,
              "greylist: pid %d - open basedir %s failed: %s\n",
              ppid,basedir,strerror(errno) );
      exit (0);
    }

/* Parse user supplied timing values */
  min_reject = get_numeric_option(ENV_MIN_REJECT, DEFAULT_MIN_REJECT);
  max_wait = get_numeric_option(ENV_MAX_WAIT, DEFAULT_MAX_WAIT);
  accept_good = get_numeric_option(ENV_ACCEPT_GOOD, DEFAULT_ACCEPT_GOOD);

int result = check_ip(addr);

if (result < 0)
    {
      /* No match found -> reject and add entry */
      if( add_ip(addr) )
        { 
          printf("E451 Greylisting in progress. Please try again later.\n");
          fprintf (stderr,
                  "greylist: pid %d - %s new - temp error\n",
                   ppid, addr);
        }
   	// if creating fails, we accept the mail anyway to be failsafe.   
    } 
  else if (result == 0)
    {
      /* Match found, but min_reject is not expired -> reject again */
      printf("E451 Greylisting in progress. Please try again later.\n");
      fprintf (stderr,
              "greylist: pid %d - %s back too soon - temp error\n",
              ppid, addr);
    } 
  else
    {
     /* Match found and min_reject expired and max_wait or accept_good not
      * expired */
     if ( update_ip(addr) )
       {
         fprintf (stderr,
                 "greylist: pid %d - Accepted %s\n",
                 ppid, addr);
       }
     // if updating fails, we accept the mail anyway to be failsafe.   
    }

exit (0);
}