upnp_redirect(const char * rhost, unsigned short eport,
              const char * iaddr, unsigned short iport,
              const char * protocol, const char * desc,
              unsigned int leaseduration)
{
	int proto, r;
	char iaddr_old[32];
	char rhost_old[32];
	unsigned short iport_old;
	struct in_addr address;
	unsigned int timestamp;

	proto = proto_atoi(protocol);
	if(inet_aton(iaddr, &address) <= 0) {
		syslog(LOG_ERR, "inet_aton(%s) FAILED", iaddr);
		return -1;
	}

	if(!check_upnp_rule_against_permissions(upnppermlist, num_upnpperm,
	                                        eport, address, iport)) {
		syslog(LOG_INFO, "redirection permission check failed for "
 		                 "%hu->%s:%hu %s", eport, iaddr, iport, protocol);
 		return -3;
 	}
 	/* IGDv1 (WANIPConnection:1 Service Template Version 1.01 / Nov 12, 2001)
 	 * - 2.2.20.PortMappingDescription :
 	 *  Overwriting Previous / Existing Port Mappings:
	 * If the RemoteHost, ExternalPort, PortMappingProtocol and InternalClient
	 * are exactly the same as an existing mapping, the existing mapping values
	 * for InternalPort, PortMappingDescription, PortMappingEnabled and
	 * PortMappingLeaseDuration are overwritten.
	 *  Rejecting a New Port Mapping:
	 * In cases where the RemoteHost, ExternalPort and PortMappingProtocol
	 * are the same as an existing mapping, but the InternalClient is
	 * different, the action is rejected with an appropriate error.
	 *  Add or Reject New Port Mapping behavior based on vendor implementation:
	 * In cases where the ExternalPort, PortMappingProtocol and InternalClient
	 * are the same, but RemoteHost is different, the vendor can choose to
	 * support both mappings simultaneously, or reject the second mapping
	 * with an appropriate error.
	 *
	 * - 2.4.16.AddPortMapping
	 * This action creates a new port mapping or overwrites an existing
	 * mapping with the same internal client. If the ExternalPort and
	 * PortMappingProtocol pair is already mapped to another internal client,
	 * an error is returned.
	 *
	 * IGDv2 (WANIPConnection:2 Service Standardized DCP (SDCP) Sep 10, 2010)
	 * Protocol ExternalPort RemoteHost InternalClient Result
	 *     =         =           ≠           ≠         Failure
	 *     =         =           ≠           =         Failure or success
	 *                                                 (vendor specific)
	 *     =         =           =           ≠         Failure
	 *     =         =           =           =         Success (overwrite)
	 */
	rhost_old[0] = '\0';
	r = get_redirect_rule(ext_if_name, eport, proto,
	                      iaddr_old, sizeof(iaddr_old), &iport_old, 0, 0,
	                      rhost_old, sizeof(rhost_old),
	                      &timestamp, 0, 0);
	if(r == 0) {
		if(strcmp(iaddr, iaddr_old)==0 &&
		   ((rhost == NULL && rhost_old[0]=='\0') ||
		    (rhost && (strcmp(rhost, "*") == 0) && rhost_old[0]=='\0') ||
		    (rhost && (strcmp(rhost, rhost_old) == 0)))) {
			syslog(LOG_INFO, "updating existing port mapping %hu %s (rhost '%s') => %s:%hu",
				eport, protocol, rhost_old, iaddr_old, iport_old);
			timestamp = (leaseduration > 0) ? upnp_time() + leaseduration : 0;
			if(iport != iport_old) {
				r = update_portmapping(ext_if_name, eport, proto, iport, desc, timestamp);
			} else {
				r = update_portmapping_desc_timestamp(ext_if_name, eport, proto, desc, timestamp);
			}
#ifdef ENABLE_LEASEFILE
			if(r == 0) {
				lease_file_remove(eport, proto);
				lease_file_add(eport, iaddr, iport, proto, desc, timestamp);
			}
#endif /* ENABLE_LEASEFILE */
			return r;
		} else {
			syslog(LOG_INFO, "port %hu %s (rhost '%s') already redirected to %s:%hu",
				eport, protocol, rhost_old, iaddr_old, iport_old);
			return -2;
		}
#ifdef CHECK_PORTINUSE
	} else if (port_in_use(ext_if_name, eport, proto, iaddr, iport) > 0) {
		syslog(LOG_INFO, "port %hu protocol %s already in use",
		       eport, protocol);
		return -4;
#endif /* CHECK_PORTINUSE */
	} else {
		timestamp = (leaseduration > 0) ? upnp_time() + leaseduration : 0;
		syslog(LOG_INFO, "redirecting port %hu to %s:%hu protocol %s for: %s",
			eport, iaddr, iport, protocol, desc);
		return upnp_redirect_internal(rhost, eport, iaddr, iport, proto,
		                              desc, timestamp);
	}
}

The product dereferences a pointer that it expects to be valid but is NULL.