options.c

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/*  $OpenBSD: options.c,v 1.15 2004/12/26 03:17:07 deraadt Exp $    */

/* DHCP options parsing and reassembly. */

/*
 * Copyright (c) 1995, 1996, 1997, 1998 The Internet Software Consortium.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of The Internet Software Consortium nor the names
 *    of its contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
 * CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * This software has been written for the Internet Software Consortium
 * by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
 * Enterprises.  To learn more about the Internet Software Consortium,
 * see ``http://www.vix.com/isc''.  To learn more about Vixie
 * Enterprises, see ``http://www.vix.com''.
 */

#define DHCP_OPTION_DATA
#include "rosdhcp.h"

int bad_options = 0;
int bad_options_max = 5;

void    parse_options(struct packet *);
void    parse_option_buffer(struct packet *, unsigned char *, int);
int store_options(unsigned char *, int, struct tree_cache **,
        unsigned char *, int, int, int, int);


/*
 * Parse all available options out of the specified packet.
 */
void
parse_options(struct packet *packet)
{
    /* Initially, zero all option pointers. */
    memset(packet->options, 0, sizeof(packet->options));

    /* If we don't see the magic cookie, there's nothing to parse. */
    if (memcmp(packet->raw->options, DHCP_OPTIONS_COOKIE, 4)) {
        packet->options_valid = 0;
        return;
    }

    /*
     * Go through the options field, up to the end of the packet or
     * the End field.
     */
    parse_option_buffer(packet, &packet->raw->options[4],
        packet->packet_length - DHCP_FIXED_NON_UDP - 4);

    /*
     * If we parsed a DHCP Option Overload option, parse more
     * options out of the buffer(s) containing them.
     */
    if (packet->options_valid &&
        packet->options[DHO_DHCP_OPTION_OVERLOAD].data) {
        if (packet->options[DHO_DHCP_OPTION_OVERLOAD].data[0] & 1)
            parse_option_buffer(packet,
                (unsigned char *)packet->raw->file,
                sizeof(packet->raw->file));
        if (packet->options[DHO_DHCP_OPTION_OVERLOAD].data[0] & 2)
            parse_option_buffer(packet,
                (unsigned char *)packet->raw->sname,
                sizeof(packet->raw->sname));
    }
}

/*
 * Parse options out of the specified buffer, storing addresses of
 * option values in packet->options and setting packet->options_valid if
 * no errors are encountered.
 */
void
parse_option_buffer(struct packet *packet,
    unsigned char *buffer, int length)
{
    unsigned char *s, *t, *end = buffer + length;
    int len, code;

    for (s = buffer; *s != DHO_END && s < end; ) {
        code = s[0];

        /* Pad options don't have a length - just skip them. */
        if (code == DHO_PAD) {
            s++;
            continue;
        }
        if (s + 2 > end) {
            len = 65536;
            goto bogus;
        }

        /*
         * All other fields (except end, see above) have a
         * one-byte length.
         */
        len = s[1];

        /*
         * If the length is outrageous, silently skip the rest,
         * and mark the packet bad. Unfortunately some crappy
         * dhcp servers always seem to give us garbage on the
         * end of a packet. so rather than keep refusing, give
         * up and try to take one after seeing a few without
         * anything good.
         */
        if (s + len + 2 > end) {
            bogus:
            bad_options++;
            warning("option %s (%d) %s.",
                dhcp_options[code].name, len,
                "larger than buffer");
            if (bad_options == bad_options_max) {
                packet->options_valid = 1;
                bad_options = 0;
                warning("Many bogus options seen in offers. "
                    "Taking this offer in spite of bogus "
                    "options - hope for the best!");
            } else {
                warning("rejecting bogus offer.");
                packet->options_valid = 0;
            }
            return;
        }
        /*
         * If we haven't seen this option before, just make
         * space for it and copy it there.
         */
        if (!packet->options[code].data) {
            if (!(t = calloc(1, len + 1)))
                error("Can't allocate storage for option %s.",
                    dhcp_options[code].name);
            /*
             * Copy and NUL-terminate the option (in case
             * it's an ASCII string.
             */
            memcpy(t, &s[2], len);
            t[len] = 0;
            packet->options[code].len = len;
            packet->options[code].data = t;
        } else {
            /*
             * If it's a repeat, concatenate it to whatever
             * we last saw.   This is really only required
             * for clients, but what the heck...
             */
            t = calloc(1, len + packet->options[code].len + 1);
            if (!t) {
                error("Can't expand storage for option %s.",
                    dhcp_options[code].name);
                                return;
                        }
            memcpy(t, packet->options[code].data,
                packet->options[code].len);
            memcpy(t + packet->options[code].len,
                &s[2], len);
            packet->options[code].len += len;
            t[packet->options[code].len] = 0;
            free(packet->options[code].data);
            packet->options[code].data = t;
        }
        s += len + 2;
    }
    packet->options_valid = 1;
}

/*
 * cons options into a big buffer, and then split them out into the
 * three separate buffers if needed.  This allows us to cons up a set of
 * vendor options using the same routine.
 */
int
cons_options(struct packet *inpacket, struct dhcp_packet *outpacket,
    int mms, struct tree_cache **options,
    int overload, /* Overload flags that may be set. */
    int terminate, int bootpp, u_int8_t *prl, int prl_len)
{
    unsigned char priority_list[300], buffer[4096];
    int priority_len, main_buffer_size, mainbufix, bufix;
    int option_size, length;

    /*
     * If the client has provided a maximum DHCP message size, use
     * that; otherwise, if it's BOOTP, only 64 bytes; otherwise use
     * up to the minimum IP MTU size (576 bytes).
     *
     * XXX if a BOOTP client specifies a max message size, we will
     * honor it.
     */
    if (!mms &&
        inpacket &&
        inpacket->options[DHO_DHCP_MAX_MESSAGE_SIZE].data &&
        (inpacket->options[DHO_DHCP_MAX_MESSAGE_SIZE].len >=
        sizeof(u_int16_t)))
        mms = getUShort(
            inpacket->options[DHO_DHCP_MAX_MESSAGE_SIZE].data);

    if (mms)
        main_buffer_size = mms - DHCP_FIXED_LEN;
    else if (bootpp)
        main_buffer_size = 64;
    else
        main_buffer_size = 576 - DHCP_FIXED_LEN;

    if (main_buffer_size > sizeof(buffer))
        main_buffer_size = sizeof(buffer);

    /* Preload the option priority list with mandatory options. */
    priority_len = 0;
    priority_list[priority_len++] = DHO_DHCP_MESSAGE_TYPE;
    priority_list[priority_len++] = DHO_DHCP_SERVER_IDENTIFIER;
    priority_list[priority_len++] = DHO_DHCP_LEASE_TIME;
    priority_list[priority_len++] = DHO_DHCP_MESSAGE;

    /*
     * If the client has provided a list of options that it wishes
     * returned, use it to prioritize.  Otherwise, prioritize based
     * on the default priority list.
     */
    if (inpacket &&
        inpacket->options[DHO_DHCP_PARAMETER_REQUEST_LIST].data) {
        int prlen =
            inpacket->options[DHO_DHCP_PARAMETER_REQUEST_LIST].len;
        if (prlen + priority_len > sizeof(priority_list))
            prlen = sizeof(priority_list) - priority_len;

        memcpy(&priority_list[priority_len],
            inpacket->options[DHO_DHCP_PARAMETER_REQUEST_LIST].data,
            prlen);
        priority_len += prlen;
        prl = priority_list;
    } else if (prl) {
        if (prl_len + priority_len > sizeof(priority_list))
            prl_len = sizeof(priority_list) - priority_len;

        memcpy(&priority_list[priority_len], prl, prl_len);
        priority_len += prl_len;
        prl = priority_list;
    } else {
        memcpy(&priority_list[priority_len],
            dhcp_option_default_priority_list,
            sizeof_dhcp_option_default_priority_list);
        priority_len += sizeof_dhcp_option_default_priority_list;
    }

    /* Copy the options into the big buffer... */
    option_size = store_options(
        buffer,
        (main_buffer_size - 7 + ((overload & 1) ? DHCP_FILE_LEN : 0) +
        ((overload & 2) ? DHCP_SNAME_LEN : 0)),
        options, priority_list, priority_len, main_buffer_size,
        (main_buffer_size + ((overload & 1) ? DHCP_FILE_LEN : 0)),
        terminate);

    /* Put the cookie up front... */
    memcpy(outpacket->options, DHCP_OPTIONS_COOKIE, 4);
    mainbufix = 4;

    /*
     * If we're going to have to overload, store the overload option
     * at the beginning.  If we can, though, just store the whole
     * thing in the packet's option buffer and leave it at that.
     */
    if (option_size <= main_buffer_size - mainbufix) {
        memcpy(&outpacket->options[mainbufix],
            buffer, option_size);
        mainbufix += option_size;
        if (mainbufix < main_buffer_size)
            outpacket->options[mainbufix++] = DHO_END;
        length = DHCP_FIXED_NON_UDP + mainbufix;
    } else {
        outpacket->options[mainbufix++] = DHO_DHCP_OPTION_OVERLOAD;
        outpacket->options[mainbufix++] = 1;
        if (option_size >
            main_buffer_size - mainbufix + DHCP_FILE_LEN)
            outpacket->options[mainbufix++] = 3;
        else
            outpacket->options[mainbufix++] = 1;

        memcpy(&outpacket->options[mainbufix],
            buffer, main_buffer_size - mainbufix);
        bufix = main_buffer_size - mainbufix;
        length = DHCP_FIXED_NON_UDP + mainbufix;
        if (overload & 1) {
            if (option_size - bufix <= DHCP_FILE_LEN) {
                memcpy(outpacket->file,
                    &buffer[bufix], option_size - bufix);
                mainbufix = option_size - bufix;
                if (mainbufix < DHCP_FILE_LEN)
                    outpacket->file[mainbufix++] = (char)DHO_END;
                while (mainbufix < DHCP_FILE_LEN)
                    outpacket->file[mainbufix++] = (char)DHO_PAD;
            } else {
                memcpy(outpacket->file,
                    &buffer[bufix], DHCP_FILE_LEN);
                bufix += DHCP_FILE_LEN;
            }
        }
        if ((overload & 2) && option_size < bufix) {
            memcpy(outpacket->sname,
                &buffer[bufix], option_size - bufix);

            mainbufix = option_size - bufix;
            if (mainbufix < DHCP_SNAME_LEN)
                outpacket->file[mainbufix++] = (char)DHO_END;
            while (mainbufix < DHCP_SNAME_LEN)
                outpacket->file[mainbufix++] = (char)DHO_PAD;
        }
    }
    return (length);
}

/*
 * Store all the requested options into the requested buffer.
 */
int
store_options(unsigned char *buffer, int buflen, struct tree_cache **options,
    unsigned char *priority_list, int priority_len, int first_cutoff,
    int second_cutoff, int terminate)
{
    int bufix = 0, option_stored[256], i, ix, tto;

    /* Zero out the stored-lengths array. */
    memset(option_stored, 0, sizeof(option_stored));

    /*
     * Copy out the options in the order that they appear in the
     * priority list...
     */
    for (i = 0; i < priority_len; i++) {
        /* Code for next option to try to store. */
        int code = priority_list[i];
        int optstart;

        /*
         * Number of bytes left to store (some may already have
         * been stored by a previous pass).
         */
        int length;

        /* If no data is available for this option, skip it. */
        if (!options[code]) {
            continue;
        }

        /*
         * The client could ask for things that are mandatory,
         * in which case we should avoid storing them twice...
         */
        if (option_stored[code])
            continue;
        option_stored[code] = 1;

        /* We should now have a constant length for the option. */
        length = options[code]->len;

        /* Do we add a NUL? */
        if (terminate && dhcp_options[code].format[0] == 't') {
            length++;
            tto = 1;
        } else
            tto = 0;

        /* Try to store the option. */

        /*
         * If the option's length is more than 255, we must
         * store it in multiple hunks.   Store 255-byte hunks
         * first.  However, in any case, if the option data will
         * cross a buffer boundary, split it across that
         * boundary.
         */
        ix = 0;

        optstart = bufix;
        while (length) {
            unsigned char incr = length > 255 ? 255 : length;

            /*
             * If this hunk of the buffer will cross a
             * boundary, only go up to the boundary in this
             * pass.
             */
            if (bufix < first_cutoff &&
                bufix + incr > first_cutoff)
                incr = first_cutoff - bufix;
            else if (bufix < second_cutoff &&
                bufix + incr > second_cutoff)
                incr = second_cutoff - bufix;

            /*
             * If this option is going to overflow the
             * buffer, skip it.
             */
            if (bufix + 2 + incr > buflen) {
                bufix = optstart;
                break;
            }

            /* Everything looks good - copy it in! */
            buffer[bufix] = code;
            buffer[bufix + 1] = incr;
            if (tto && incr == length) {
                memcpy(buffer + bufix + 2,
                    options[code]->value + ix, incr - 1);
                buffer[bufix + 2 + incr - 1] = 0;
            } else
                memcpy(buffer + bufix + 2,
                    options[code]->value + ix, incr);
            length -= incr;
            ix += incr;
            bufix += 2 + incr;
        }
    }
    return (bufix);
}

/*
 * Format the specified option so that a human can easily read it.
 */
char *
pretty_print_option(unsigned int code, unsigned char *data, int len,
    int emit_commas, int emit_quotes)
{
    static char optbuf[32768]; /* XXX */
    int hunksize = 0, numhunk = -1, numelem = 0;
    char fmtbuf[32], *op = optbuf;
    int i, j, k, opleft = sizeof(optbuf);
    unsigned char *dp = data;
    struct in_addr foo;
    char comma;

    /* Code should be between 0 and 255. */
    if (code > 255)
        error("pretty_print_option: bad code %d", code);

    if (emit_commas)
        comma = ',';
    else
        comma = ' ';

    /* Figure out the size of the data. */
    for (i = 0; dhcp_options[code].format[i]; i++) {
        if (!numhunk) {
            warning("%s: Excess information in format string: %s",
                dhcp_options[code].name,
                &(dhcp_options[code].format[i]));
            break;
        }
        numelem++;
        fmtbuf[i] = dhcp_options[code].format[i];
        switch (dhcp_options[code].format[i]) {
        case 'A':
            --numelem;
            fmtbuf[i] = 0;
            numhunk = 0;
            break;
        case 'X':
            for (k = 0; k < len; k++)
                if (!isascii(data[k]) ||
                    !isprint(data[k]))
                    break;
            if (k == len) {
                fmtbuf[i] = 't';
                numhunk = -2;
            } else {
                fmtbuf[i] = 'x';
                hunksize++;
                comma = ':';
                numhunk = 0;
            }
            fmtbuf[i + 1] = 0;
            break;
        case 't':
            fmtbuf[i] = 't';
            fmtbuf[i + 1] = 0;
            numhunk = -2;
            break;
        case 'I':
        case 'l':
        case 'L':
            hunksize += 4;
            break;
        case 's':
        case 'S':
            hunksize += 2;
            break;
        case 'b':
        case 'B':
        case 'f':
            hunksize++;
            break;
        case 'e':
            break;
        default:
            warning("%s: garbage in format string: %s",
                dhcp_options[code].name,
                &(dhcp_options[code].format[i]));
            break;
        }
    }

    /* Check for too few bytes... */
    if (hunksize > len) {
        warning("%s: expecting at least %d bytes; got %d",
            dhcp_options[code].name, hunksize, len);
        return ("<error>");
    }
    /* Check for too many bytes... */
    if (numhunk == -1 && hunksize < len)
        warning("%s: %d extra bytes",
            dhcp_options[code].name, len - hunksize);

    /* If this is an array, compute its size. */
    if (!numhunk)
        numhunk = len / hunksize;
    /* See if we got an exact number of hunks. */
    if (numhunk > 0 && numhunk * hunksize < len)
        warning("%s: %d extra bytes at end of array",
            dhcp_options[code].name, len - numhunk * hunksize);

    /* A one-hunk array prints the same as a single hunk. */
    if (numhunk < 0)
        numhunk = 1;

    /* Cycle through the array (or hunk) printing the data. */
    for (i = 0; i < numhunk; i++) {
        for (j = 0; j < numelem; j++) {
            int opcount;
            switch (fmtbuf[j]) {
            case 't':
                if (emit_quotes) {
                    *op++ = '"';
                    opleft--;
                }
                for (; dp < data + len; dp++) {
                    if (!isascii(*dp) ||
                        !isprint(*dp)) {
                        if (dp + 1 != data + len ||
                            *dp != 0) {
                            _snprintf(op, opleft,
                                "\\%03o", *dp);
                            op += 4;
                            opleft -= 4;
                        }
                    } else if (*dp == '"' ||
                        *dp == '\'' ||
                        *dp == '$' ||
                        *dp == '`' ||
                        *dp == '\\') {
                        *op++ = '\\';
                        *op++ = *dp;
                        opleft -= 2;
                    } else {
                        *op++ = *dp;
                        opleft--;
                    }
                }
                if (emit_quotes) {
                    *op++ = '"';
                    opleft--;
                }

                *op = 0;
                break;
            case 'I':
                foo.s_addr = htonl(getULong(dp));
                strncpy(op, inet_ntoa(foo), opleft - 1);
                op[opleft - 1] = ANSI_NULL;
                opcount = strlen(op);
                if (opcount >= opleft)
                    goto toobig;
                opleft -= opcount;
                dp += 4;
                break;
            case 'l':
                opcount = _snprintf(op, opleft, "%ld",
                    (long)getLong(dp));
                if (opcount >= opleft || opcount == -1)
                    goto toobig;
                opleft -= opcount;
                dp += 4;
                break;
            case 'L':
                opcount = _snprintf(op, opleft, "%ld",
                    (unsigned long)getULong(dp));
                if (opcount >= opleft || opcount == -1)
                    goto toobig;
                opleft -= opcount;
                dp += 4;
                break;
            case 's':
                opcount = _snprintf(op, opleft, "%d",
                    getShort(dp));
                if (opcount >= opleft || opcount == -1)
                    goto toobig;
                opleft -= opcount;
                dp += 2;
                break;
            case 'S':
                opcount = _snprintf(op, opleft, "%d",
                    getUShort(dp));
                if (opcount >= opleft || opcount == -1)
                    goto toobig;
                opleft -= opcount;
                dp += 2;
                break;
            case 'b':
                opcount = _snprintf(op, opleft, "%d",
                    *(char *)dp++);
                if (opcount >= opleft || opcount == -1)
                    goto toobig;
                opleft -= opcount;
                break;
            case 'B':
                opcount = _snprintf(op, opleft, "%d", *dp++);
                if (opcount >= opleft || opcount == -1)
                    goto toobig;
                opleft -= opcount;
                break;
            case 'x':
                opcount = _snprintf(op, opleft, "%x", *dp++);
                if (opcount >= opleft || opcount == -1)
                    goto toobig;
                opleft -= opcount;
                break;
            case 'f':
                opcount = (size_t) strncpy(op, *dp++ ? "true" : "false", opleft - 1);
                op[opleft - 1] = ANSI_NULL;
                if (opcount >= opleft)
                    goto toobig;
                opleft -= opcount;
                break;
            default:
                warning("Unexpected format code %c", fmtbuf[j]);
            }
            op += strlen(op);
            opleft -= strlen(op);
            if (opleft < 1)
                goto toobig;
            if (j + 1 < numelem && comma != ':') {
                *op++ = ' ';
                opleft--;
            }
        }
        if (i + 1 < numhunk) {
            *op++ = comma;
            opleft--;
        }
        if (opleft < 1)
            goto toobig;

    }
    return (optbuf);
 toobig:
    warning("dhcp option too large");
    return ("<error>");
}

void
do_packet(struct interface_info *interface, struct dhcp_packet *packet,
    int len, unsigned int from_port, struct iaddr from, struct hardware *hfrom)
{
    struct packet tp;
    int i;

    if (packet->hlen > sizeof(packet->chaddr)) {
        note("Discarding packet with invalid hlen.");
        return;
    }

    memset(&tp, 0, sizeof(tp));
    tp.raw = packet;
    tp.packet_length = len;
    tp.client_port = from_port;
    tp.client_addr = from;
    tp.interface = interface;
    tp.haddr = hfrom;

    parse_options(&tp);
    if (tp.options_valid &&
        tp.options[DHO_DHCP_MESSAGE_TYPE].data)
        tp.packet_type = tp.options[DHO_DHCP_MESSAGE_TYPE].data[0];
    if (tp.packet_type)
        dhcp(&tp);
    else
        bootp(&tp);

    /* Free the data associated with the options. */
    for (i = 0; i < 256; i++)
        if (tp.options[i].len && tp.options[i].data)
            free(tp.options[i].data);
}