discovery.c

实现点到点的以太网协议,用于拨号上网,是拨号上网的基础部分软件模块.

    pc.seenServiceName = 0;
	
    do {
	if (BPF_BUFFER_IS_EMPTY) {
	    tv.tv_sec = timeout;
	    tv.tv_usec = 0;
	
	    FD_ZERO(&readable);
	    FD_SET(conn->discoverySocket, &readable);

	    while(1) {
		r = select(conn->discoverySocket+1, &readable, NULL, NULL, &tv);
		if (r >= 0 || errno != EINTR) break;
	    }
	    if (r < 0) {
		fatalSys("select (waitForPADO)");
	    }
	    if (r == 0) return;        /* Timed out */
	}
	
	/* Get the packet */
	receivePacket(conn->discoverySocket, &packet, &len);

	/* Check length */
	if (ntohs(packet.length) + HDR_SIZE > len) {
	    syslog(LOG_ERR, "Bogus PPPoE length field (%u)",
		   (unsigned int) ntohs(packet.length));
	    continue;
	}

#ifdef USE_BPF
	/* If it's not a Discovery packet, loop again */
	if (etherType(&packet) != Eth_PPPOE_Discovery) continue;
#endif

	if (conn->debugFile) {
	    dumpPacket(conn->debugFile, &packet, "RCVD");
	    fprintf(conn->debugFile, "\n");
	    fflush(conn->debugFile);
	}
	/* If it's not for us, loop again */
	if (!packetIsForMe(conn, &packet)) continue;

	if (packet.code == CODE_PADO) {
	    if (BROADCAST(packet.ethHdr.h_source)) {
		printErr("Ignoring PADO packet from broadcast MAC address");
		continue;
	    }
	    parsePacket(&packet, parsePADOTags, &pc);
	    if (!pc.seenACName) {
		printErr("Ignoring PADO packet with no AC-Name tag");
		continue;
	    }
	    if (!pc.seenServiceName) {
		printErr("Ignoring PADO packet with no Service-Name tag");
		continue;
	    }
	    conn->numPADOs++;
	    if (conn->printACNames) {
		printf("--------------------------------------------------\n");
	    }
	    if (pc.acNameOK && pc.serviceNameOK) {
		memcpy(conn->peerEth, packet.ethHdr.h_source, ETH_ALEN);
		if (conn->printACNames) {
		    printf("AC-Ethernet-Address: %02x:%02x:%02x:%02x:%02x:%02x\n",
			   (unsigned) conn->peerEth[0], 
			   (unsigned) conn->peerEth[1],
			   (unsigned) conn->peerEth[2],
			   (unsigned) conn->peerEth[3],
			   (unsigned) conn->peerEth[4],
			   (unsigned) conn->peerEth[5]);
		    continue;
		}
		conn->discoveryState = STATE_RECEIVED_PADO;
		break;
	    }
	}
    } while (conn->discoveryState != STATE_RECEIVED_PADO);
}

/***********************************************************************
*%FUNCTION: sendPADR
*%ARGUMENTS:
* conn -- PPPoE connection structur
*%RETURNS:
* Nothing
*%DESCRIPTION:
* Sends a PADR packet
***********************************************************************/
void
sendPADR(PPPoEConnection *conn)
{
    PPPoEPacket packet;
    PPPoETag *svc = (PPPoETag *) packet.payload;
    unsigned char *cursor = packet.payload;

    UINT16_t namelen = 0;
    UINT16_t plen;

    if (conn->serviceName) {
	namelen = (UINT16_t) strlen(conn->serviceName);
    }
    plen = TAG_HDR_SIZE + namelen;
    CHECK_ROOM(cursor, packet.payload, plen);

    memcpy(packet.ethHdr.h_dest, conn->peerEth, ETH_ALEN);
    memcpy(packet.ethHdr.h_source, conn->myEth, ETH_ALEN);

    packet.ethHdr.h_proto = htons(Eth_PPPOE_Discovery);
    packet.ver = 1;
    packet.type = 1;
    packet.code = CODE_PADR;
    packet.session = 0;

    svc->type = TAG_SERVICE_NAME;
    svc->length = htons(namelen);
    if (conn->serviceName) {
	memcpy(svc->payload, conn->serviceName, namelen);
    }
    cursor += namelen + TAG_HDR_SIZE;

    /* If we're using Host-Uniq, copy it over */
    if (conn->useHostUniq) {
	PPPoETag hostUniq;
	pid_t pid = getpid();
	hostUniq.type = htons(TAG_HOST_UNIQ);
	hostUniq.length = htons(sizeof(pid));
	memcpy(hostUniq.payload, &pid, sizeof(pid));
	CHECK_ROOM(cursor, packet.payload, sizeof(pid)+TAG_HDR_SIZE);
	memcpy(cursor, &hostUniq, sizeof(pid) + TAG_HDR_SIZE);
	cursor += sizeof(pid) + TAG_HDR_SIZE;
	plen += sizeof(pid) + TAG_HDR_SIZE;
    }

    /* Copy cookie and relay-ID if needed */
    if (conn->cookie.type) {
	CHECK_ROOM(cursor, packet.payload,
		   ntohs(conn->cookie.length) + TAG_HDR_SIZE);
	memcpy(cursor, &conn->cookie, ntohs(conn->cookie.length) + TAG_HDR_SIZE);
	cursor += ntohs(conn->cookie.length) + TAG_HDR_SIZE;
	plen += ntohs(conn->cookie.length) + TAG_HDR_SIZE;
    }

    if (conn->relayId.type) {
	CHECK_ROOM(cursor, packet.payload,
		   ntohs(conn->relayId.length) + TAG_HDR_SIZE);
	memcpy(cursor, &conn->relayId, ntohs(conn->relayId.length) + TAG_HDR_SIZE);
	cursor += ntohs(conn->relayId.length) + TAG_HDR_SIZE;
	plen += ntohs(conn->relayId.length) + TAG_HDR_SIZE;
    }

    packet.length = htons(plen);
    sendPacket(conn, conn->discoverySocket, &packet, (int) (plen + HDR_SIZE));
    if (conn->debugFile) {
	dumpPacket(conn->debugFile, &packet, "SENT");
	fprintf(conn->debugFile, "\n");
	fflush(conn->debugFile);
    }
}

/**********************************************************************
*%FUNCTION: waitForPADS
*%ARGUMENTS:
* conn -- PPPoE connection info
* timeout -- how long to wait (in seconds)
*%RETURNS:
* Nothing
*%DESCRIPTION:
* Waits for a PADS packet and copies useful information
***********************************************************************/
void
waitForPADS(PPPoEConnection *conn, int timeout)
{
    fd_set readable;
    int r;
    struct timeval tv;
    PPPoEPacket packet;
    int len;

    do {
	if (BPF_BUFFER_IS_EMPTY) {
	    tv.tv_sec = timeout;
	    tv.tv_usec = 0;
	    
	    FD_ZERO(&readable);
	    FD_SET(conn->discoverySocket, &readable);
	    
	    while(1) {
		r = select(conn->discoverySocket+1, &readable, NULL, NULL, &tv);
		if (r >= 0 || errno != EINTR) break;
	    }
	    if (r < 0) {
		fatalSys("select (waitForPADS)");
	    }
	    if (r == 0) return;
	}

	/* Get the packet */
	receivePacket(conn->discoverySocket, &packet, &len);

	/* Check length */
	if (ntohs(packet.length) + HDR_SIZE > len) {
	    syslog(LOG_ERR, "Bogus PPPoE length field (%u)",
		   (unsigned int) ntohs(packet.length));
	    continue;
	}

#ifdef USE_BPF
	/* If it's not a Discovery packet, loop again */
	if (etherType(&packet) != Eth_PPPOE_Discovery) continue;
#endif
	if (conn->debugFile) {
	    dumpPacket(conn->debugFile, &packet, "RCVD");
	    fprintf(conn->debugFile, "\n");
	    fflush(conn->debugFile);
	}

	/* If it's not from the AC, it's not for me */
	if (memcmp(packet.ethHdr.h_source, conn->peerEth, ETH_ALEN)) continue;

	/* If it's not for us, loop again */
	if (!packetIsForMe(conn, &packet)) continue;

	/* Is it PADS?  */
	if (packet.code == CODE_PADS) {
	    /* Parse for goodies */
	    parsePacket(&packet, parsePADSTags, conn);
	    conn->discoveryState = STATE_SESSION;
	    break;
	}
    } while (conn->discoveryState != STATE_SESSION);

    /* Don't bother with ntohs; we'll just end up converting it back... */
    conn->session = packet.session;

    syslog(LOG_INFO, "PPP session is %d", (int) ntohs(conn->session));

    /* RFC 2516 says session id MUST NOT be zero or 0xFFFF */
    if (ntohs(conn->session) == 0 || ntohs(conn->session) == 0xFFFF) {
	syslog(LOG_ERR, "Access concentrator used a session value of %x -- the AC is violating RFC 2516", (unsigned int) ntohs(conn->session));
    }
}

/**********************************************************************
*%FUNCTION: discovery
*%ARGUMENTS:
* conn -- PPPoE connection info structure
*%RETURNS:
* Nothing
*%DESCRIPTION:
* Performs the PPPoE discovery phase
***********************************************************************/
void
discovery(PPPoEConnection *conn)
{
    int padiAttempts = 0;
    int padrAttempts = 0;
    int timeout = PADI_TIMEOUT;

    /* Skip discovery and don't open discovery socket? */
    if (conn->skipDiscovery && conn->noDiscoverySocket) {
	conn->discoveryState = STATE_SESSION;
	return;
    }

    conn->discoverySocket =
	openInterface(conn->ifName, Eth_PPPOE_Discovery, conn->myEth);

    /* Skip discovery? */
    if (conn->skipDiscovery) {
	conn->discoveryState = STATE_SESSION;
	return;
    }

    do {
	padiAttempts++;
	if (padiAttempts > MAX_PADI_ATTEMPTS) {
	    warn("Timeout waiting for PADO packets");
	    close(conn->discoverySocket);
	    conn->discoverySocket = -1;
	    return;
	}
	sendPADI(conn);
	conn->discoveryState = STATE_SENT_PADI;
	waitForPADO(conn, timeout);

	/* If we're just probing for access concentrators, don't do
	   exponential backoff.  This reduces the time for an unsuccessful
	   probe to 15 seconds. */
	if (!conn->printACNames) {
	    timeout *= 2;
	}
	if (conn->printACNames && conn->numPADOs) {
	    break;
	}
    } while (conn->discoveryState == STATE_SENT_PADI);

    /* If we're only printing access concentrator names, we're done */
    if (conn->printACNames) {
	die(0);
    }

    timeout = PADI_TIMEOUT;
    do {
	padrAttempts++;
	if (padrAttempts > MAX_PADI_ATTEMPTS) {
	    warn("Timeout waiting for PADS packets");
	    close(conn->discoverySocket);
	    conn->discoverySocket = -1;
	    return;
	}
	sendPADR(conn);
	conn->discoveryState = STATE_SENT_PADR;
	waitForPADS(conn, timeout);
	timeout *= 2;
    } while (conn->discoveryState == STATE_SENT_PADR);

    /* We're done. */
    conn->discoveryState = STATE_SESSION;
    return;
}