Another checkcompat() Example

#define OUR_NETWORK 0x86f50000	/* change this	*/
#define OUR_NETMASK 0xffff0000	/* change this	*/

int
checkcompat(to, e)
	register ADDRESS *to;
	register ENVELOPE *e;
{
	extern unsigned long inet_addr();
	extern char *inet_ntoa();
	struct hostent *h;
	struct in_addr *p;
	struct passwd *pass;
	char *remote_user, *remote_host;
	char *tmp;
	int reject_relay, ok, i;
	
# ifdef lint
	if (to == NULL)
		to++;
# endif /* lint */

	if(tTd(49, 1))
	{
		printf("=========== Smart checkcompat()\n");
		printf("from=%s\n",e->e_from.q_paddr);
		printf("to=%s\n",to->q_paddr);
		printf("RealHostName = %s\n",RealHostName);
		printf("net addr = %s (%x)\n",
			inet_ntoa(RealHostAddr.sin.sin_addr),RealHostAddr.sin.sin_addr);
		printf("msg size = %d, rcpts = %d\n",e->e_msgsize,e->e_nrcpts);
		printf("EF_QUEUERUN flag = %d\n",bitset(EF_QUEUERUN,e->e_flags));
		printf("EF_INQUEUE flag = %d\n",bitset(EF_INQUEUE,e->e_flags));
	}

	/* allow all "return to sender" messages */
	if(bitset(EF_RESPONSE, e->e_flags)) return(EX_OK);

	/* is this a locally submitted message */
	if(RealHostAddr.sa.sa_family == 0) return(EX_OK);

	/* is the localmailer flag activated?  */
	/* If so, then the mail is to be received locally so it is ok */
	if(tTd(49, 1))
	{
		printf("===localmailer flag test\n");
		printf("localmailer flag = %d (%s)\n",
			bitnset(M_LOCALMAILER,to->q_mailer->m_flags),
			bitnset(M_LOCALMAILER,to->q_mailer->m_flags));
	}
	if(bitnset(M_LOCALMAILER,to->q_mailer->m_flags)) 
	{
		return(EX_OK);
	}

	/* is the sending host in our Domain? If so, then ok */
	if(tTd(49, 1))
	{
		printf("===realhostaddr test\n");
		printf("net addr = %s (%x)\n",
			inet_ntoa(RealHostAddr.sin.sin_addr),RealHostAddr.sin.sin_addr);
	}
	if(RealHostAddr.sa.sa_family == AF_INET &&
		(RealHostAddr.sin.sin_addr.s_addr & OUR_NETMASK) == OUR_NETWORK)
	{
		return(EX_OK);
	}
	
	/* neither the "from" nor the "to" addresses are local */
	/* did the "to" address derive from a local alias?  If so, */
	/* then we want to relay aliased/forwarded e-mail */
	if(tTd(49, 1))
	{
		printf("===alias test\n");
		printf("alias=%s\n",to->q_alias->q_paddr);
	}
	if(to->q_alias->q_paddr != NULL)
	{
		syslog(LOG_INFO, "%s: RELAY (alias): from=%s, to=%s",
			e->e_id, 
			e->e_from.q_paddr == NULL ? "<NONE>" :
			shortenstring(e->e_from.q_paddr, 83),
			to->q_paddr);
		return(EX_OK);
	}

	/* at this point we know we have a relay attempt going here */
	/* we will still allow the relay *iff* the domain matches our */
	/* allowed domain name *and* we can verify that the alleged */
	/* user/mail forger is a real user in our domain.  So split up */
	/* e->e_sender into "user" and "domain".  See if the user exists */
	/* and the domain matches our domain(s). */
	if(tTd(49, 1))
	{
		printf("===forged user/domain test\n");
		printf("sender = %s\n",e->e_sender);
	}
	/* first convert the sender address to lowercase */
	tmp = strdup(e->e_sender);
	i = 0;
	while(tmp[i] != '\0')
	{
		tmp[i] = tolower(tmp[i]);
		i++;
	}
	/* now tokenize the string: always assumes form of "user@domain" */
	reject_relay = 0;
	remote_user = strtok(tmp,"@");
	remote_host = strtok(NULL, "@");
	if(tTd(49, 1))
	{
		printf("remote user = %s, remote host = %s\n",
			remote_user,remote_host);
	}

	/* reject if the alleged user is "root" or */
	/* user not found in /etc/passwd file */
	if(strncmp(remote_user,"root",4) == 0) reject_relay = 1;
	setpwent();
	if((pass = sm_getpwnam(remote_user)) == NULL) reject_relay = 1;

	if(tTd(49, 1))
	{
		printf("after user lookup, reject_relay = %d\n",reject_relay);
	}

	/* now examine the hostname/domain portion of the sender */
	if(reject_relay == 0)
	{
    	/* pull the hostent structure of the remote host */
	    if((h = gethostbyname(remote_host)) == NULL) reject_relay = 1;
	
		/* now compare IP addresses to those of our domain */
		ok = 0;
	    for(i = 0; h->h_addr_list[i] != NULL; i++)
	    {
			p = (struct in_addr *) h->h_addr_list[i];
			/* found a match */
			if((p->s_addr & OUR_NETMASK) == OUR_NETWORK)
			{
				ok = 1;
				break;
			}
	    }
		if(ok == 0) reject_relay = 1;
		if(tTd(49, 1))
		{
			printf("after hostname check, reject_relay = %d\n",reject_relay);
		}
	}

	/* clean up our memory usage from above */
	free(tmp);

	/* if reject_relay is still zero, then accept the forgery */
	if(reject_relay == 0)
	{
		syslog(LOG_INFO, "%s: RELAY (forged: %s): from=%s, to=%s",
			e->e_id, 
			RealHostName,
			e->e_from.q_paddr == NULL ? "<NONE>" :
			shortenstring(e->e_from.q_paddr, 83),
			to->q_paddr);
		return(EX_OK);
	}
	
	/**********************************************/
	/* if we get to here, we do not want the mail */
	/**********************************************/
	if(tTd(49, 1))
	{
		printf("checkcompat() rejecting email\n");
		printf("from=%s, to=%s\n",e->e_from.q_paddr,to->q_paddr);
	}
	usrerr("553 We do not relay remote-site mail");
	/* e->e_flags |= EF_NO_BODY_RETN; */
	to->q_status = "5.7.1";
	syslog(LOG_NOTICE, "%s: RELAY (rejection: %s): from=%s, to=%s",
		e->e_id, 
		RealHostName,
		e->e_from.q_paddr == NULL ? "<NONE>" :
		shortenstring(e->e_from.q_paddr, 83),
		to->q_paddr);
	return(EX_UNAVAILABLE);
}