sm_statefuns.c

一种在UDP协议中实现了拥赛控制和重传机制的协议

/* SCTP kernel reference Implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * Copyright (c) 2001-2002 Intel Corp.
 * Copyright (c) 2002      Nokia Corp.
 *
 * This file is part of the SCTP kernel reference Implementation
 *
 * This is part of the SCTP Linux Kernel Reference Implementation.
 *
 * These are the state functions for the state machine.
 *
 * The SCTP reference implementation 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, or (at your option)
 * any later version.
 *
 * The SCTP reference implementation 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 GNU CC; see the file COPYING.  If not, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <[e-mail]>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <[e-mail]>
 *    Karl Knutson          <[e-mail]>
 *    Mathew Kotowsky       <[e-mail]>
 *    Sridhar Samudrala     <[e-mail]>
 *    Jon Grimm             <[e-mail]>
 *    Hui Huang 	    <[e-mail]>
 *    Dajiang Zhang 	    <[e-mail]>
 *    Daisy Chang	    <[e-mail]>
 *    Ardelle Fan	    <[e-mail]>
 *    Ryan Layer	    <[e-mail]>
 *    Kevin Gao		    <[e-mail]>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/net.h>
#include <linux/inet.h>
#include <net/sock.h>
#include <net/inet_ecn.h>
#include <linux/skbuff.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>
#include <net/sctp/structs.h>

static struct sctp_packet *sctp_abort_pkt_new(const struct sctp_endpoint *ep,
				  const struct sctp_association *asoc,
				  struct sctp_chunk *chunk,
				  const void *payload,
				  size_t paylen);
static int sctp_eat_data(const struct sctp_association *asoc,
			 struct sctp_chunk *chunk,
			 sctp_cmd_seq_t *commands);
static struct sctp_packet *sctp_ootb_pkt_new(const struct sctp_association *asoc,
					     const struct sctp_chunk *chunk);
static void sctp_send_stale_cookie_err(const struct sctp_endpoint *ep,
				       const struct sctp_association *asoc,
				       const struct sctp_chunk *chunk,
				       sctp_cmd_seq_t *commands,
				       struct sctp_chunk *err_chunk);
static sctp_disposition_t sctp_sf_do_5_2_6_stale(const struct sctp_endpoint *ep,
						 const struct sctp_association *asoc,
						 const sctp_subtype_t type,
						 void *arg,
						 sctp_cmd_seq_t *commands);
static sctp_disposition_t sctp_sf_shut_8_4_5(const struct sctp_endpoint *ep,
					     const struct sctp_association *asoc,
					     const sctp_subtype_t type,
					     void *arg,
					     sctp_cmd_seq_t *commands);
static struct sctp_sackhdr *sctp_sm_pull_sack(struct sctp_chunk *chunk);


/* Small helper function that checks if the chunk length
 * is of the appropriate length.  The 'required_length' argument
 * is set to be the size of a specific chunk we are testing.
 * Return Values:  1 = Valid length
 * 		   0 = Invalid length
 *
 */
static inline int
sctp_chunk_length_valid(struct sctp_chunk *chunk,
			   __u16 required_length)
{
	__u16 chunk_length = ntohs(chunk->chunk_hdr->length);

	if (unlikely(chunk_length < required_length))
		return 0;

	return 1;
}

/**********************************************************
 * These are the state functions for handling chunk events.
 **********************************************************/

/*
 * Process the final SHUTDOWN COMPLETE.
 *
 * Section: 4 (C) (diagram), 9.2
 * Upon reception of the SHUTDOWN COMPLETE chunk the endpoint will verify
 * that it is in SHUTDOWN-ACK-SENT state, if it is not the chunk should be
 * discarded. If the endpoint is in the SHUTDOWN-ACK-SENT state the endpoint
 * should stop the T2-shutdown timer and remove all knowledge of the
 * association (and thus the association enters the CLOSED state).
 *
 * Verification Tag: 8.5.1(C), sctpimpguide 2.41.
 * C) Rules for packet carrying SHUTDOWN COMPLETE:
 * ...
 * - The receiver of a SHUTDOWN COMPLETE shall accept the packet
 *   if the Verification Tag field of the packet matches its own tag and
 *   the T bit is not set
 *   OR
 *   it is set to its peer's tag and the T bit is set in the Chunk
 *   Flags.
 *   Otherwise, the receiver MUST silently discard the packet
 *   and take no further action.  An endpoint MUST ignore the
 *   SHUTDOWN COMPLETE if it is not in the SHUTDOWN-ACK-SENT state.
 *
 * 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_4_C(const struct sctp_endpoint *ep,
				  const struct sctp_association *asoc,
				  const sctp_subtype_t type,
				  void *arg,
				  sctp_cmd_seq_t *commands)
{
	struct sctp_chunk *chunk = arg;
	struct sctp_ulpevent *ev;

	/* RFC 2960 6.10 Bundling
	 *
	 * An endpoint MUST NOT bundle INIT, INIT ACK or
	 * SHUTDOWN COMPLETE with any other chunks.
	 */
	if (!chunk->singleton)
		return SCTP_DISPOSITION_VIOLATION;

	if (!sctp_vtag_verify_either(chunk, asoc))
		return sctp_sf_pdiscard(ep, asoc, type, arg, commands);

	/* RFC 2960 10.2 SCTP-to-ULP
	 *
	 * H) SHUTDOWN COMPLETE notification
	 *
	 * When SCTP completes the shutdown procedures (section 9.2) this
	 * notification is passed to the upper layer.
	 */
	ev = sctp_ulpevent_make_assoc_change(asoc, 0, SCTP_SHUTDOWN_COMP,
					     0, 0, 0, GFP_ATOMIC);
	if (!ev)
		goto nomem;

	sctp_add_cmd_sf(commands, SCTP_CMD_EVENT_ULP, SCTP_ULPEVENT(ev));

	/* Upon reception of the SHUTDOWN COMPLETE chunk the endpoint
	 * will verify that it is in SHUTDOWN-ACK-SENT state, if it is
	 * not the chunk should be discarded. If the endpoint is in
	 * the SHUTDOWN-ACK-SENT state the endpoint should stop the
	 * T2-shutdown timer and remove all knowledge of the
	 * association (and thus the association enters the CLOSED
	 * state).
	 */
	sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_STOP,
			SCTP_TO(SCTP_EVENT_TIMEOUT_T2_SHUTDOWN));

	sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_STOP,
			SCTP_TO(SCTP_EVENT_TIMEOUT_T5_SHUTDOWN_GUARD));

	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_STATE,
			SCTP_STATE(SCTP_STATE_CLOSED));

	SCTP_INC_STATS(SCTP_MIB_SHUTDOWNS);
	SCTP_DEC_STATS(SCTP_MIB_CURRESTAB);

	sctp_add_cmd_sf(commands, SCTP_CMD_DELETE_TCB, SCTP_NULL());

	return SCTP_DISPOSITION_DELETE_TCB;

nomem:
	return SCTP_DISPOSITION_NOMEM;
}

/*
 * Respond to a normal INIT chunk.
 * We are the side that is being asked for an association.
 *
 * Section: 5.1 Normal Establishment of an Association, B
 * B) "Z" shall respond immediately with an INIT ACK chunk.  The
 *    destination IP address of the INIT ACK MUST be set to the source
 *    IP address of the INIT to which this INIT ACK is responding.  In
 *    the response, besides filling in other parameters, "Z" must set the
 *    Verification Tag field to Tag_A, and also provide its own
 *    Verification Tag (Tag_Z) in the Initiate Tag field.
 *
 * Verification Tag: Must be 0. 
 *
 * 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_1B_init(const struct sctp_endpoint *ep,
					const struct sctp_association *asoc,
					const sctp_subtype_t type,
					void *arg,
					sctp_cmd_seq_t *commands)
{
	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;
	struct sock *sk;
	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);

	/* If the packet is an OOTB packet which is temporarily on the
	 * control endpoint, respond with an ABORT.
	 */
	if (ep == sctp_sk((sctp_get_ctl_sock()))->ep)
		return sctp_sf_tabort_8_4_8(ep, asoc, type, arg, commands);

	sk = ep->base.sk;
	/* If the endpoint is not listening or if the number of associations
	 * on the TCP-style socket exceed the max backlog, respond with an
	 * ABORT.
	 */
	if (!sctp_sstate(sk, LISTENING) ||
	    (sctp_style(sk, TCP) &&
	     sk_acceptq_is_full(sk)))
		return sctp_sf_tabort_8_4_8(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.
	 * Normally, this would cause an ABORT with a Protocol Violation
	 * error, but since we don't have an association, we'll
	 * just discard the packet.
	 */
	if (!sctp_chunk_length_valid(chunk, sizeof(sctp_init_chunk_t)))
		return sctp_sf_pdiscard(ep, asoc, type, arg, commands);

	/* 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));

			sctp_chunk_free(err_chunk);

			if (packet) {
				sctp_add_cmd_sf(commands, SCTP_CMD_SEND_PKT,
						SCTP_PACKET(packet));
				SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);
				return SCTP_DISPOSITION_CONSUME;
			} else {
				return SCTP_DISPOSITION_NOMEM;
			}
		} else {
			return sctp_sf_tabort_8_4_8(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));

	new_asoc = sctp_make_temp_asoc(ep, chunk, GFP_ATOMIC);
	if (!new_asoc)
		goto nomem;

	/* The call, sctp_process_init(), can fail on memory allocation.  */
	if (!sctp_process_init(new_asoc, chunk->chunk_hdr->type,
			       sctp_source(chunk),
			       (sctp_init_chunk_t *)chunk->chunk_hdr,
			       GFP_ATOMIC))
		goto nomem_init;

	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_ASOC, SCTP_ASOC(new_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_ack;

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

	/* 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_chunk_free(err_chunk);
	}

	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, nor keep any states for the
	 * new association.  Otherwise, "Z" will be vulnerable to resource
	 * attacks.
	 */
	sctp_add_cmd_sf(commands, SCTP_CMD_DELETE_TCB, SCTP_NULL());

	return SCTP_DISPOSITION_DELETE_TCB;

nomem_ack:
	if (err_chunk)
		sctp_chunk_free(err_chunk);
nomem_init:
	sctp_association_free(new_asoc);
nomem:
	return SCTP_DISPOSITION_NOMEM;
}

/*
 * Respond to a normal INIT ACK chunk.
 * We are the side that is initiating the association.
 *
 * Section: 5.1 Normal Establishment of an Association, C
 * C) Upon reception of the INIT ACK from "Z", "A" shall stop the T1-init
 *    timer and leave COOKIE-WAIT state. "A" shall then send the State
 *    Cookie received in the INIT ACK chunk in a COOKIE ECHO chunk, start