common.c

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	sum += (UINT32_t) tmp;
	addr += sizeof(tmp);
	count -= sizeof(tmp);
    }
    if (count > 0) {
	sum += (unsigned char) *addr;
    }

    while(sum >> 16) {
	sum = (sum & 0xffff) + (sum >> 16);
    }
    return (UINT16_t) ((~sum) & 0xFFFF);
}

/**********************************************************************
*%FUNCTION: clampMSS
*%ARGUMENTS:
* packet -- PPPoE session packet
* dir -- either "incoming" or "outgoing"
* clampMss -- clamp value
*%RETURNS:
* Nothing
*%DESCRIPTION:
* Clamps MSS option if TCP SYN flag is set.
***********************************************************************/
void
clampMSS(PPPoEPacket *packet, char const *dir, int clampMss)
{
    unsigned char *tcpHdr;
    unsigned char *ipHdr;
    unsigned char *opt;
    unsigned char *endHdr;
    unsigned char *mssopt = NULL;
    UINT16_t csum;

    int len, minlen;

    /* check PPP protocol type */
    if (packet->payload[0] & 0x01) {
        /* 8 bit protocol type */

        /* Is it IPv4? */
        if (packet->payload[0] != 0x21) {
            /* Nope, ignore it */
            return;
        }

        ipHdr = packet->payload + 1;
	minlen = 41;
    } else {
        /* 16 bit protocol type */

        /* Is it IPv4? */
        if (packet->payload[0] != 0x00 ||
            packet->payload[1] != 0x21) {
            /* Nope, ignore it */
            return;
        }

        ipHdr = packet->payload + 2;
	minlen = 42;
    }

    /* Is it too short? */
    len = (int) ntohs(packet->length);
    if (len < minlen) {
	/* 20 byte IP header; 20 byte TCP header; at least 1 or 2 byte PPP protocol */
	return;
    }

    /* Verify once more that it's IPv4 */
    if ((ipHdr[0] & 0xF0) != 0x40) {
	return;
    }

    /* Is it a fragment that's not at the beginning of the packet? */
    if ((ipHdr[6] & 0x1F) || ipHdr[7]) {
	/* Yup, don't touch! */
	return;
    }
    /* Is it TCP? */
    if (ipHdr[9] != 0x06) {
	return;
    }

    /* Get start of TCP header */
    tcpHdr = ipHdr + (ipHdr[0] & 0x0F) * 4;

    /* Is SYN set? */
    if (!(tcpHdr[13] & 0x02)) {
	return;
    }

    /* Compute and verify TCP checksum -- do not touch a packet with a bad
       checksum */
    csum = computeTCPChecksum(ipHdr, tcpHdr);
    if (csum) {
	syslog(LOG_ERR, "Bad TCP checksum %x", (unsigned int) csum);

	/* Upper layers will drop it */
	return;
    }

    /* Look for existing MSS option */
    endHdr = tcpHdr + ((tcpHdr[12] & 0xF0) >> 2);
    opt = tcpHdr + 20;
    while (opt < endHdr) {
	if (!*opt) break;	/* End of options */
	switch(*opt) {
	case 1:
	    opt++;
	    break;

	case 2:
	    if (opt[1] != 4) {
		/* Something fishy about MSS option length. */
		syslog(LOG_ERR,
		       "Bogus length for MSS option (%u) from %u.%u.%u.%u",
		       (unsigned int) opt[1],
		       (unsigned int) ipHdr[12],
		       (unsigned int) ipHdr[13],
		       (unsigned int) ipHdr[14],
		       (unsigned int) ipHdr[15]);
		return;
	    }
	    mssopt = opt;
	    break;
	default:
	    if (opt[1] < 2) {
		/* Someone's trying to attack us? */
		syslog(LOG_ERR,
		       "Bogus TCP option length (%u) from %u.%u.%u.%u",
		       (unsigned int) opt[1],
		       (unsigned int) ipHdr[12],
		       (unsigned int) ipHdr[13],
		       (unsigned int) ipHdr[14],
		       (unsigned int) ipHdr[15]);
		return;
	    }
	    opt += (opt[1]);
	    break;
	}
	/* Found existing MSS option? */
	if (mssopt) break;
    }

    /* If MSS exists and it's low enough, do nothing */
    if (mssopt) {
	unsigned mss = mssopt[2] * 256 + mssopt[3];
	if (mss <= clampMss) {
	    return;
	}

	mssopt[2] = (((unsigned) clampMss) >> 8) & 0xFF;
	mssopt[3] = ((unsigned) clampMss) & 0xFF;
    } else {
	/* No MSS option.  Don't add one; we'll have to use 536. */
	return;
    }

    /* Recompute TCP checksum */
    tcpHdr[16] = 0;
    tcpHdr[17] = 0;
    csum = computeTCPChecksum(ipHdr, tcpHdr);
    (* (UINT16_t *) (tcpHdr+16)) = csum;
}

/***********************************************************************
*%FUNCTION: sendPADT
*%ARGUMENTS:
* conn -- PPPoE connection
* msg -- if non-NULL, extra error message to include in PADT packet.
*%RETURNS:
* Nothing
*%DESCRIPTION:
* Sends a PADT packet
***********************************************************************/
void
sendPADT(PPPoEConnection *conn, char const *msg)
{
    PPPoEPacket packet;
    unsigned char *cursor = packet.payload;

    UINT16_t plen = 0;

    /* Do nothing if no session established yet */
    if (!conn->session) return;

    /* Do nothing if no discovery socket */
    if (conn->discoverySocket < 0) return;

    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_PADT;
    packet.session = conn->session;

    /* Reset Session to zero so there is no possibility of
       recursive calls to this function by any signal handler */
    conn->session = 0;

    /* 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));
	memcpy(cursor, &hostUniq, sizeof(pid) + TAG_HDR_SIZE);
	cursor += sizeof(pid) + TAG_HDR_SIZE;
	plen += sizeof(pid) + TAG_HDR_SIZE;
    }

    /* Copy error message */
    if (msg) {
	PPPoETag err;
	size_t elen = strlen(msg);
	err.type = htons(TAG_GENERIC_ERROR);
	err.length = htons(elen);
	strcpy((char *) err.payload, msg);
	memcpy(cursor, &err, elen + TAG_HDR_SIZE);
	cursor += elen + TAG_HDR_SIZE;
	plen += elen + 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);
    }
    syslog(LOG_INFO,"Sent PADT");
}

/***********************************************************************
*%FUNCTION: sendPADTf
*%ARGUMENTS:
* conn -- PPPoE connection
* msg -- printf-style format string
* args -- arguments for msg
*%RETURNS:
* Nothing
*%DESCRIPTION:
* Sends a PADT packet with a formatted message
***********************************************************************/
void
sendPADTf(PPPoEConnection *conn, char const *fmt, ...)
{
    char msg[512];
    va_list ap;

    va_start(ap, fmt);
    vsnprintf(msg, sizeof(msg), fmt, ap);
    va_end(ap);
    msg[511] = 0;

    sendPADT(conn, msg);
}

/**********************************************************************
*%FUNCTION: parseLogErrs
*%ARGUMENTS:
* type -- tag type
* len -- tag length
* data -- tag data
* extra -- extra user data
*%RETURNS:
* Nothing
*%DESCRIPTION:
* Picks error tags out of a packet and logs them.
***********************************************************************/
void
parseLogErrs(UINT16_t type, UINT16_t len, unsigned char *data,
	     void *extra)
{
    switch(type) {
    case TAG_SERVICE_NAME_ERROR:
	syslog(LOG_ERR, "PADT: Service-Name-Error: %.*s", (int) len, data);
	fprintf(stderr, "PADT: Service-Name-Error: %.*s\n", (int) len, data);
	break;
    case TAG_AC_SYSTEM_ERROR:
	syslog(LOG_ERR, "PADT: System-Error: %.*s", (int) len, data);
	fprintf(stderr, "PADT: System-Error: %.*s\n", (int) len, data);
	break;
    case TAG_GENERIC_ERROR:
	syslog(LOG_ERR, "PADT: Generic-Error: %.*s", (int) len, data);
	fprintf(stderr, "PADT: Generic-Error: %.*s\n", (int) len, data);
	break;
    }
}