sm_statefuns.c

在linux环境下的流控制传输协议（sctp）的源代码

	 */
	pkt = sctp_abort_pkt_new(ep, NULL, init, errhdr, len);

	if (!pkt)
		goto out;
	sctp_add_cmd_sf(commands, SCTP_CMD_SEND_PKT, SCTP_PACKET(pkt));

	SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);

	/* Discard the rest of the inbound packet. */
	sctp_add_cmd_sf(commands, SCTP_CMD_DISCARD_PACKET, SCTP_NULL());

out:
	/* Even if there is no memory, treat as a failure so
	 * the packet will get dropped.
	 */
	return 0;
}

/* A restart is occurring, check to make sure no new addresses
 * are being added as we may be under a takeover attack.
 */
static int sctp_sf_check_restart_addrs(const struct sctp_association *new_asoc,
				       const struct sctp_association *asoc,
				       struct sctp_chunk *init,
				       sctp_cmd_seq_t *commands)
{
	struct sctp_transport *new_addr, *addr;
	struct list_head *pos, *pos2;
	int found;

	/* Implementor's Guide - Sectin 5.2.2
	 * ...
	 * Before responding the endpoint MUST check to see if the
	 * unexpected INIT adds new addresses to the association. If new
	 * addresses are added to the association, the endpoint MUST respond
	 * with an ABORT..
	 */

	/* Search through all current addresses and make sure
	 * we aren't adding any new ones.
	 */
	new_addr = NULL;
	found = 0;

	list_for_each(pos, &new_asoc->peer.transport_addr_list) {
		new_addr = list_entry(pos, struct sctp_transport, transports);
		found = 0;
		list_for_each(pos2, &asoc->peer.transport_addr_list) {
			addr = list_entry(pos2, struct sctp_transport,
					  transports);
			if (sctp_cmp_addr_exact(&new_addr->ipaddr,
						&addr->ipaddr)) {
				found = 1;
				break;
			}
		}
		if (!found)
			break;
	}

	/* If a new address was added, ABORT the sender. */
	if (!found && new_addr) {
		sctp_sf_send_restart_abort(&new_addr->ipaddr, init, commands);
	}

	/* Return success if all addresses were found. */
	return found;
}

/* Populate the verification/tie tags based on overlapping INIT
 * scenario.
 *
 * Note: Do not use in CLOSED or SHUTDOWN-ACK-SENT state.
 */
static void sctp_tietags_populate(struct sctp_association *new_asoc,
				  const struct sctp_association *asoc)
{
	switch (asoc->state) {

	/* 5.2.1 INIT received in COOKIE-WAIT or COOKIE-ECHOED State */

	case SCTP_STATE_COOKIE_WAIT:
		new_asoc->c.my_vtag     = asoc->c.my_vtag;
		new_asoc->c.my_ttag     = asoc->c.my_vtag;
		new_asoc->c.peer_ttag   = 0;
		break;

	case SCTP_STATE_COOKIE_ECHOED:
		new_asoc->c.my_vtag     = asoc->c.my_vtag;
		new_asoc->c.my_ttag     = asoc->c.my_vtag;
		new_asoc->c.peer_ttag   = asoc->c.peer_vtag;
		break;

	/* 5.2.2 Unexpected INIT in States Other than CLOSED, COOKIE-ECHOED,
	 * COOKIE-WAIT and SHUTDOWN-ACK-SENT
	 */
	default:
		new_asoc->c.my_ttag   = asoc->c.my_vtag;
		new_asoc->c.peer_ttag = asoc->c.peer_vtag;
		break;
	}

	/* Other parameters for the endpoint SHOULD be copied from the
	 * existing parameters of the association (e.g. number of
	 * outbound streams) into the INIT ACK and cookie.
	 */
	new_asoc->rwnd                  = asoc->rwnd;
	new_asoc->c.sinit_num_ostreams  = asoc->c.sinit_num_ostreams;
	new_asoc->c.sinit_max_instreams = asoc->c.sinit_max_instreams;
	new_asoc->c.initial_tsn         = asoc->c.initial_tsn;
}

/*
 * Compare vtag/tietag values to determine unexpected COOKIE-ECHO
 * handling action.
 *
 * RFC 2960 5.2.4 Handle a COOKIE ECHO when a TCB exists.
 *
 * Returns value representing action to be taken.   These action values
 * correspond to Action/Description values in RFC 2960, Table 2.
 */
static char sctp_tietags_compare(struct sctp_association *new_asoc,
				 const struct sctp_association *asoc)
{
	/* In this case, the peer may have restarted.  */
	if ((asoc->c.my_vtag != new_asoc->c.my_vtag) &&
	    (asoc->c.peer_vtag != new_asoc->c.peer_vtag) &&
	    (asoc->c.my_vtag == new_asoc->c.my_ttag) &&
	    (asoc->c.peer_vtag == new_asoc->c.peer_ttag))
		return 'A';

	/* Collision case B. */
	if ((asoc->c.my_vtag == new_asoc->c.my_vtag) &&
	    ((asoc->c.peer_vtag != new_asoc->c.peer_vtag) ||
	     (0 == asoc->c.peer_vtag))) {
		return 'B';
	}

	/* Collision case D. */
	if ((asoc->c.my_vtag == new_asoc->c.my_vtag) &&
	    (asoc->c.peer_vtag == new_asoc->c.peer_vtag))
		return 'D';

	/* Collision case C. */
	if ((asoc->c.my_vtag != new_asoc->c.my_vtag) &&
	    (asoc->c.peer_vtag == new_asoc->c.peer_vtag) &&
	    (0 == new_asoc->c.my_ttag) &&
	    (0 == new_asoc->c.peer_ttag))
		return 'C';

	/* No match to any of the special cases; discard this packet. */
	return 'E';
}

/* Common helper routine for both duplicate and simulataneous INIT
 * chunk handling.
 */
static sctp_disposition_t sctp_sf_do_unexpected_init(
	const struct sctp_endpoint *ep,
	const struct sctp_association *asoc,
	const sctp_subtype_t type,
	void *arg, sctp_cmd_seq_t *commands)
{
	sctp_disposition_t retval;
	struct sctp_chunk *chunk = arg;
	struct sctp_chunk *repl;
	struct sctp_association *new_asoc;
	struct sctp_chunk *err_chunk;
	struct sctp_packet *packet;
	sctp_unrecognized_param_t *unk_param;
	int len;

	/* 6.10 Bundling
	 * An endpoint MUST NOT bundle INIT, INIT ACK or
	 * SHUTDOWN COMPLETE with any other chunks.
	 *
	 * IG Section 2.11.2
	 * Furthermore, we require that the receiver of an INIT chunk MUST
	 * enforce these rules by silently discarding an arriving packet
	 * with an INIT chunk that is bundled with other chunks.
	 */
	if (!chunk->singleton)
		return sctp_sf_pdiscard(ep, asoc, type, arg, commands);

	/* 3.1 A packet containing an INIT chunk MUST have a zero Verification
	 * Tag.
	 */
	if (chunk->sctp_hdr->vtag != 0)
		return sctp_sf_tabort_8_4_8(ep, asoc, type, arg, commands);

	/* Make sure that the INIT chunk has a valid length.
	 * In this case, we generate a protocol violation since we have
	 * an association established.
	 */
	if (!sctp_chunk_length_valid(chunk, sizeof(sctp_init_chunk_t)))
		return sctp_sf_violation_chunklen(ep, asoc, type, arg,
						  commands);
	/* Grab the INIT header.  */
	chunk->subh.init_hdr = (sctp_inithdr_t *) chunk->skb->data;

	/* Tag the variable length parameters.  */
	chunk->param_hdr.v = skb_pull(chunk->skb, sizeof(sctp_inithdr_t));

	/* Verify the INIT chunk before processing it. */
	err_chunk = NULL;
	if (!sctp_verify_init(asoc, chunk->chunk_hdr->type,
			      (sctp_init_chunk_t *)chunk->chunk_hdr, chunk,
			      &err_chunk)) {
		/* This chunk contains fatal error. It is to be discarded.
		 * Send an ABORT, with causes if there is any.
		 */
		if (err_chunk) {
			packet = sctp_abort_pkt_new(ep, asoc, arg,
					(__u8 *)(err_chunk->chunk_hdr) +
					sizeof(sctp_chunkhdr_t),
					ntohs(err_chunk->chunk_hdr->length) -
					sizeof(sctp_chunkhdr_t));

			if (packet) {
				sctp_add_cmd_sf(commands, SCTP_CMD_SEND_PKT,
						SCTP_PACKET(packet));
				SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);
				retval = SCTP_DISPOSITION_CONSUME;
			} else {
				retval = SCTP_DISPOSITION_NOMEM;
			}
			goto cleanup;
		} else {
			return sctp_sf_tabort_8_4_8(ep, asoc, type, arg,
						    commands);
		}
	}

	/*
	 * Other parameters for the endpoint SHOULD be copied from the
	 * existing parameters of the association (e.g. number of
	 * outbound streams) into the INIT ACK and cookie.
	 * FIXME:  We are copying parameters from the endpoint not the
	 * association.
	 */
	new_asoc = sctp_make_temp_asoc(ep, chunk, GFP_ATOMIC);
	if (!new_asoc)
		goto nomem;

	/* In the outbound INIT ACK the endpoint MUST copy its current
	 * Verification Tag and Peers Verification tag into a reserved
	 * place (local tie-tag and per tie-tag) within the state cookie.
	 */
	if (!sctp_process_init(new_asoc, chunk->chunk_hdr->type,
			       sctp_source(chunk),
			       (sctp_init_chunk_t *)chunk->chunk_hdr,
			       GFP_ATOMIC))
		goto nomem;

	/* Make sure no new addresses are being added during the
	 * restart.   Do not do this check for COOKIE-WAIT state,
	 * since there are no peer addresses to check against.
	 * Upon return an ABORT will have been sent if needed.
	 */
	if (!sctp_state(asoc, COOKIE_WAIT)) {
		if (!sctp_sf_check_restart_addrs(new_asoc, asoc, chunk,
						 commands)) {
			retval = SCTP_DISPOSITION_CONSUME;
			goto nomem_retval;
		}
	}

	sctp_tietags_populate(new_asoc, asoc);

	/* B) "Z" shall respond immediately with an INIT ACK chunk.  */

	/* If there are errors need to be reported for unknown parameters,
	 * make sure to reserve enough room in the INIT ACK for them.
	 */
	len = 0;
	if (err_chunk) {
		len = ntohs(err_chunk->chunk_hdr->length) -
			sizeof(sctp_chunkhdr_t);
	}

	if (sctp_assoc_set_bind_addr_from_ep(new_asoc, GFP_ATOMIC) < 0)
		goto nomem;

	repl = sctp_make_init_ack(new_asoc, chunk, GFP_ATOMIC, len);
	if (!repl)
		goto nomem;

	/* If there are errors need to be reported for unknown parameters,
	 * include them in the outgoing INIT ACK as "Unrecognized parameter"
	 * parameter.
	 */
	if (err_chunk) {
		/* Get the "Unrecognized parameter" parameter(s) out of the
		 * ERROR chunk generated by sctp_verify_init(). Since the
		 * error cause code for "unknown parameter" and the
		 * "Unrecognized parameter" type is the same, we can
		 * construct the parameters in INIT ACK by copying the
		 * ERROR causes over.
		 */
		unk_param = (sctp_unrecognized_param_t *)
			    ((__u8 *)(err_chunk->chunk_hdr) +
			    sizeof(sctp_chunkhdr_t));
		/* Replace the cause code with the "Unrecognized parameter"
		 * parameter type.
		 */
		sctp_addto_chunk(repl, len, unk_param);
	}

	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_ASOC, SCTP_ASOC(new_asoc));
	sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(repl));

	/*
	 * Note: After sending out INIT ACK with the State Cookie parameter,
	 * "Z" MUST NOT allocate any resources for this new association.
	 * Otherwise, "Z" will be vulnerable to resource attacks.
	 */
	sctp_add_cmd_sf(commands, SCTP_CMD_DELETE_TCB, SCTP_NULL());
	retval = SCTP_DISPOSITION_CONSUME;

	return retval;

nomem:
	retval = SCTP_DISPOSITION_NOMEM;
nomem_retval:
	if (new_asoc)
		sctp_association_free(new_asoc);
cleanup:
	if (err_chunk)
		sctp_chunk_free(err_chunk);
	return retval;
}

/*
 * Handle simultanous INIT.
 * This means we started an INIT and then we got an INIT request from
 * our peer.
 *
 * Section: 5.2.1 INIT received in COOKIE-WAIT or COOKIE-ECHOED State (Item B)
 * This usually indicates an initialization collision, i.e., each
 * endpoint is attempting, at about the same time, to establish an
 * association with the other endpoint.
 *
 * Upon receipt of an INIT in the COOKIE-WAIT or COOKIE-ECHOED state, an
 * endpoint MUST respond with an INIT ACK using the same parameters it
 * sent in its original INIT chunk (including its Verification Tag,
 * unchanged). These original parameters are combined with those from the
 * newly received INIT chunk. The endpoint shall also generate a State
 * Cookie with the INIT ACK. The endpoint uses the parameters sent in its
 * INIT to calculate the State Cookie.
 *
 * After that, the endpoint MUST NOT change its state, the T1-init
 * timer shall be left running and the corresponding TCB MUST NOT be
 * destroyed. The normal procedures for handling State Cookies when
 * a TCB exists will resolve the duplicate INITs to a single association.
 *
 * For an endpoint that is in the COOKIE-ECHOED state it MUST populate
 * its Tie-Tags with the Tag information of itself and its peer (see
 * section 5.2.2 for a description of the Tie-Tags).
 *
 * Verification Tag: Not explicit, but an INIT can not have a valid
 * verification tag, so we skip the check.
 *
 * Inputs
 * (endpoint, asoc, chunk)
 *
 * Outputs
 * (asoc, reply_msg, msg_up, timers, counters)
 *
 * The return value is the disposition of the chunk.
 */
sctp_disposition_t sctp_sf_do_5_2_1_siminit(const struct sctp_endpoint *ep,
				    const struct sctp_association *asoc,
				    const sctp_subtype_t type,
				    void *arg,
				    sctp_cmd_seq_t *commands)
{
	/* Call helper to do the real work for both simulataneous and
	 * duplicate INIT chunk handling.
	 */
	return sctp_sf_do_unexpected_init(ep, asoc, type, arg, commands);
}

/*
 * Handle duplicated INIT messages.  These are usually delayed
 * restransmissions.
 *
 * Section: 5.2.2 Unexpected INIT in States Other than CLOSED,
 * COOKIE-ECHOED and COOKIE-WAIT
 *
 * Unless otherwise stated, upon reception of an unexpected INIT for
 * this association, the endpoint shall generate an INIT ACK with a
 * State Cookie.  In the outbound INIT ACK the endpoint MUST copy its
 * current Verification Tag and peer's Verification Tag into a reserved
 * place within the state cookie.  We shall refer to these locations as
 * the Peer's-Tie-Tag and the Local-Tie-Tag.  The outbound SCTP packet
 * containing this INIT ACK MUST carry a Verification Tag value equal to
 * the Initiation Tag found in the unexpected INIT.  And the INIT ACK
 * MUST contain a new Initiation Tag (randomly generated see Section
 * 5.3.1).  Other parameters for the endpoint SHOULD be copied from the