dhcrelay.c

DHCP服务器源码

		packet -> hops = packet -> hops + 1;
	else
		return;

	/* Otherwise, it's a BOOTREQUEST, so forward it to all the
	   servers. */
	for (sp = servers; sp; sp = sp -> next) {
		if (send_packet ((fallback_interface
				  ? fallback_interface : interfaces),
				 (struct packet *)0,
				 packet, length, ip -> primary_address,
				 &sp -> to, (struct hardware *)0) < 0) {
			++client_packet_errors;
		} else {
			log_debug ("forwarded BOOTREQUEST for %s to %s",
			       print_hw_addr (packet -> htype, packet -> hlen,
					      packet -> chaddr),
			       inet_ntoa (sp -> to.sin_addr));
			++client_packets_relayed;
		}
	}
				 
}

static void usage ()
{
	log_fatal ("Usage: dhcrelay [-p <port>] [-d] [-D] [-i %s%s%s%s",
		"interface] [-q] [-a]\n                ",
		"[-c count] [-A length] ",
		"[-m append|replace|forward|discard]\n",
		"                [server1 [... serverN]]");
}

int write_lease (lease)
	struct lease *lease;
{
	return 1;
}

int write_host (host)
	struct host_decl *host;
{
	return 1;
}

int commit_leases ()
{
	return 1;
}

void bootp (packet)
	struct packet *packet;
{
}

void dhcp (packet)
	struct packet *packet;
{
}

int find_subnet (struct subnet **sp,
		 struct iaddr addr, const char *file, int line)
{
	return 0;
}

#if defined (DEBUG)
int check_collection (struct packet *p, struct lease *l,
		      struct collection *c)
{
	return 0;
}

void classify (struct packet *p, struct class *c)
{
}

isc_result_t find_class (struct class **class, const char *c1,
			 const char *c2, int i)
{
	return ISC_R_NOTFOUND;
}

int parse_allow_deny (struct option_cache **oc, struct parse *p, int i)
{
	return 0;
}

/* As a wise man once said in dhcpctl/omshell.c: */
/* Sigh */
isc_result_t dhcp_set_control_state (control_object_state_t oldstate,
				     control_object_state_t newstate)
{
	return ISC_R_SUCCESS;
}

#endif

/* Strip any Relay Agent Information options from the DHCP packet
   option buffer.   If an RAI option is found whose Agent ID matches
   the giaddr (i.e., ours), try to look up the outgoing interface
   based on the circuit ID suboption. */

int strip_relay_agent_options (in, out, packet, length)
	struct interface_info *in, **out;
	struct dhcp_packet *packet;
	unsigned length;
{
	int is_dhcp = 0;
	u_int8_t *op, *sp, *max;
	int good_agent_option = 0;
	int status;

	/* If we're not adding agent options to packets, we're not taking
	   them out either. */
	if (!add_agent_options)
		return length;

	/* If there's no cookie, it's a bootp packet, so we should just
	   forward it unchanged. */
	if (memcmp (packet -> options, DHCP_OPTIONS_COOKIE, 4))
		return length;

	max = ((u_int8_t *)packet) + length;
	sp = op = &packet -> options [4];

	while (op < max) {
		switch (*op) {
			/* Skip padding... */
		      case DHO_PAD:
			if (sp != op)
				*sp = *op;
			++op;
			++sp;
			continue;

			/* If we see a message type, it's a DHCP packet. */
		      case DHO_DHCP_MESSAGE_TYPE:
			is_dhcp = 1;
			goto skip;
			break;

			/* Quit immediately if we hit an End option. */
		      case DHO_END:
			if (sp != op)
				*sp++ = *op++;
			goto out;

		      case DHO_DHCP_AGENT_OPTIONS:
			/* We shouldn't see a relay agent option in a
			   packet before we've seen the DHCP packet type,
			   but if we do, we have to leave it alone. */
			if (!is_dhcp)
				goto skip;

			status = find_interface_by_agent_option (packet,
								 out, op + 2,
								 op [1]);
			if (status == -1 && drop_agent_mismatches)
				return 0;
			if (status)
				good_agent_option = 1;
			op += op [1] + 2;
			break;

		      skip:
			/* Skip over other options. */
		      default:
			if (sp != op)
				memcpy (sp, op, (unsigned)(op [1] + 2));
			sp += op [1] + 2;
			op += op [1] + 2;
			break;
		}
	}
      out:

	/* If it's not a DHCP packet, we're not supposed to touch it. */
	if (!is_dhcp)
		return length;

	/* If none of the agent options we found matched, or if we didn't
	   find any agent options, count this packet as not having any
	   matching agent options, and if we're relying on agent options
	   to determine the outgoing interface, drop the packet. */

	if (!good_agent_option) {
		++missing_agent_option;
		if (drop_agent_mismatches)
			return 0;
	}

	/* Adjust the length... */
	if (sp != op) {
		length = sp - ((u_int8_t *)packet);

		/* Make sure the packet isn't short (this is unlikely,
                   but WTH) */
		if (length < BOOTP_MIN_LEN) {
			memset (sp, 0, BOOTP_MIN_LEN - length);
			length = BOOTP_MIN_LEN;
		}
	}
	return length;
}


/* Find an interface that matches the circuit ID specified in the
   Relay Agent Information option.   If one is found, store it through
   the pointer given; otherwise, leave the existing pointer alone.

   We actually deviate somewhat from the current specification here:
   if the option buffer is corrupt, we suggest that the caller not
   respond to this packet.  If the circuit ID doesn't match any known
   interface, we suggest that the caller to drop the packet.  Only if
   we find a circuit ID that matches an existing interface do we tell
   the caller to go ahead and process the packet. */

int find_interface_by_agent_option (packet, out, buf, len)
	struct dhcp_packet *packet;
	struct interface_info **out;
	u_int8_t *buf;
	int len;
{
	int i = 0;
	u_int8_t *circuit_id = 0;
	unsigned circuit_id_len;
	struct interface_info *ip;

	while (i < len) {
		/* If the next agent option overflows the end of the
		   packet, the agent option buffer is corrupt. */
		if (i + 1 == len ||
		    i + buf [i + 1] + 2 > len) {
			++corrupt_agent_options;
			return -1;
		}
		switch (buf [i]) {
			/* Remember where the circuit ID is... */
		      case RAI_CIRCUIT_ID:
			circuit_id = &buf [i + 2];
			circuit_id_len = buf [i + 1];
			i += circuit_id_len + 2;
			continue;

		      default:
			i += buf [i + 1] + 2;
			break;
		}
	}

	/* If there's no circuit ID, it's not really ours, tell the caller
	   it's no good. */
	if (!circuit_id) {
		++missing_circuit_id;
		return -1;
	}

	/* Scan the interface list looking for an interface whose
	   name matches the one specified in circuit_id. */

	for (ip = interfaces; ip; ip = ip -> next) {
		if (ip -> circuit_id &&
		    ip -> circuit_id_len == circuit_id_len &&
		    !memcmp (ip -> circuit_id, circuit_id, circuit_id_len))
			break;
	}

	/* If we got a match, use it. */
	if (ip) {
		*out = ip;
		return 1;
	}

	/* If we didn't get a match, the circuit ID was bogus. */
	++bad_circuit_id;
	return -1;
}

/* Examine a packet to see if it's a candidate to have a Relay
   Agent Information option tacked onto its tail.   If it is, tack
   the option on.  */

int add_relay_agent_options (ip, packet, length, giaddr)
	struct interface_info *ip;
	struct dhcp_packet *packet;
	unsigned length;
	struct in_addr giaddr;
{
	int is_dhcp = 0, agent_options_present = 0;
	u_int8_t *op, *sp, *max, *end_pad = 0;

	/* If we're not adding agent options to packets, we can skip
	   this. */
	if (!add_agent_options)
		return length;

	/* If there's no cookie, it's a bootp packet, so we should just
	   forward it unchanged. */
	if (memcmp (packet -> options, DHCP_OPTIONS_COOKIE, 4))
		return length;

	max = ((u_int8_t *)packet) + length;
	sp = op = &packet -> options [4];

	while (op < max) {
		switch (*op) {
			/* Skip padding... */
		      case DHO_PAD:
			end_pad = sp;
			if (sp != op)
				*sp = *op;
			++op;
			++sp;
			continue;

			/* If we see a message type, it's a DHCP packet. */
		      case DHO_DHCP_MESSAGE_TYPE:
			is_dhcp = 1;
			goto skip;
			break;

			/* Quit immediately if we hit an End option. */
		      case DHO_END:
			goto out;

		      case DHO_DHCP_AGENT_OPTIONS:
			/* We shouldn't see a relay agent option in a
			   packet before we've seen the DHCP packet type,
			   but if we do, we have to leave it alone. */
			if (!is_dhcp)
				goto skip;
			end_pad = 0;

			/* There's already a Relay Agent Information option
			   in this packet.   How embarrassing.   Decide what
			   to do based on the mode the user specified. */

			switch (agent_relay_mode) {
			      case forward_and_append:
				goto skip;
			      case forward_untouched:
				return length;
			      case discard:
				return 0;
			      case forward_and_replace:
			      default:
				break;
			}

			/* Skip over the agent option and start copying
			   if we aren't copying already. */
			op += op [1] + 2;
			break;

		      skip:
			/* Skip over other options. */
		      default:
			end_pad = 0;
			if (sp != op)
				memcpy (sp, op, (unsigned)(op [1] + 2));
			sp += op [1] + 2;
			op += op [1] + 2;
			break;
		}
	}
      out:

	/* If it's not a DHCP packet, we're not supposed to touch it. */
	if (!is_dhcp)
		return length;

	/* If the packet was padded out, we can store the agent option
	   at the beginning of the padding. */

	if (end_pad)
		sp = end_pad;

	/* Remember where the end of the packet was after parsing
	   it. */
	op = sp;

	/* XXX Is there room? */

	/* Okay, cons up *our* Relay Agent Information option. */
	*sp++ = DHO_DHCP_AGENT_OPTIONS;
	*sp++ = 0;	/* Dunno... */

	/* Copy in the circuit id... */
	*sp++ = RAI_CIRCUIT_ID;
	/* Sanity check.   Had better not every happen. */
	if (ip -> circuit_id_len > 255 || ip -> circuit_id_len < 1)
		log_fatal ("completely bogus circuit id length %d on %s\n",
		       ip -> circuit_id_len, ip -> name);
	*sp++ = ip -> circuit_id_len;
	memcpy (sp, ip -> circuit_id, ip -> circuit_id_len);
	sp += ip -> circuit_id_len;

	/* Copy in remote ID... */
	if (ip -> remote_id) {
		*sp++ = RAI_REMOTE_ID;
		if (ip -> remote_id_len > 255 || ip -> remote_id_len < 1)
			log_fatal ("bogus remote id length %d on %s\n",
			       ip -> circuit_id_len, ip -> name);
		*sp++ = ip -> remote_id_len;
		memcpy (sp, ip -> remote_id, ip -> remote_id_len);
		sp += ip -> remote_id_len;
	}

	/* Relay option's total length shouldn't ever get to be more than
	   257 bytes. */
	if (sp - op > 257)
	    log_fatal ("total agent option length exceeds 257 (%ld) on %s\n",
		       (long)(sp - op), ip -> name);

	/* Calculate length of RAI option. */
	op [1] = sp - op - 2;

	/* Deposit an END token. */
	*sp++ = DHO_END;

	/* Recalculate total packet length. */
	length = sp - ((u_int8_t *)packet);

	/* Make sure the packet isn't short (this is unlikely, but WTH) */
	if (length < BOOTP_MIN_LEN) {
		memset (sp, 0, BOOTP_MIN_LEN - length);
		length = BOOTP_MIN_LEN;
	}

	return length;
}