githubmirror/libslirp

src/bootp.c
373 строки11 KB
Marc-André Lureau
bootp: check bootp_input buffer size
14 июн 2021, 10:42
14 июн 2021, 10:422eca083
/* SPDX-License-Identifier: MIT */
/*
 * QEMU BOOTP/DHCP server
 *
 * Copyright (c) 2004 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include "slirp.h"

#if defined(_WIN32)
/* Windows ntohl() returns an u_long value.
 * Add a type cast to match the format strings. */
#define ntohl(n) ((uint32_t)ntohl(n))
#endif

/* XXX: only DHCP is supported */

#define LEASE_TIME (24 * 3600)

static const uint8_t rfc1533_cookie[] = { RFC1533_COOKIE };

#define DPRINTF(fmt, ...) DEBUG_CALL(fmt, ##__VA_ARGS__)

static BOOTPClient *get_new_addr(Slirp *slirp, struct in_addr *paddr,
                                 const uint8_t *macaddr)
{
    BOOTPClient *bc;
    int i;

    for (i = 0; i < NB_BOOTP_CLIENTS; i++) {
        bc = &slirp->bootp_clients[i];
        if (!bc->allocated || !memcmp(macaddr, bc->macaddr, 6))
            goto found;
    }
    return NULL;
found:
    bc = &slirp->bootp_clients[i];
    bc->allocated = 1;
    paddr->s_addr = slirp->vdhcp_startaddr.s_addr + htonl(i);
    return bc;
}

static BOOTPClient *request_addr(Slirp *slirp, const struct in_addr *paddr,
                                 const uint8_t *macaddr)
{
    uint32_t req_addr = ntohl(paddr->s_addr);
    uint32_t dhcp_addr = ntohl(slirp->vdhcp_startaddr.s_addr);
    BOOTPClient *bc;

    if (req_addr >= dhcp_addr && req_addr < (dhcp_addr + NB_BOOTP_CLIENTS)) {
        bc = &slirp->bootp_clients[req_addr - dhcp_addr];
        if (!bc->allocated || !memcmp(macaddr, bc->macaddr, 6)) {
            bc->allocated = 1;
            return bc;
        }
    }
    return NULL;
}

static BOOTPClient *find_addr(Slirp *slirp, struct in_addr *paddr,
                              const uint8_t *macaddr)
{
    BOOTPClient *bc;
    int i;

    for (i = 0; i < NB_BOOTP_CLIENTS; i++) {
        if (!memcmp(macaddr, slirp->bootp_clients[i].macaddr, 6))
            goto found;
    }
    return NULL;
found:
    bc = &slirp->bootp_clients[i];
    bc->allocated = 1;
    paddr->s_addr = slirp->vdhcp_startaddr.s_addr + htonl(i);
    return bc;
}

static void dhcp_decode(const struct bootp_t *bp,
                        const uint8_t *bp_end,
                        int *pmsg_type,
                        struct in_addr *preq_addr)
{
    const uint8_t *p;
    int len, tag;

    *pmsg_type = 0;
    preq_addr->s_addr = htonl(0L);

    p = bp->bp_vend;
    if (memcmp(p, rfc1533_cookie, 4) != 0)
        return;
    p += 4;
    while (p < bp_end) {
        tag = p[0];
        if (tag == RFC1533_PAD) {
            p++;
        } else if (tag == RFC1533_END) {
            break;
        } else {
            p++;
            if (p >= bp_end)
                break;
            len = *p++;
            if (p + len > bp_end) {
                break;
            }
            DPRINTF("dhcp: tag=%d len=%d\n", tag, len);

            switch (tag) {
            case RFC2132_MSG_TYPE:
                if (len >= 1)
                    *pmsg_type = p[0];
                break;
            case RFC2132_REQ_ADDR:
                if (len >= 4) {
                    memcpy(&(preq_addr->s_addr), p, 4);
                }
                break;
            default:
                break;
            }
            p += len;
        }
    }
    if (*pmsg_type == DHCPREQUEST && preq_addr->s_addr == htonl(0L) &&
        bp->bp_ciaddr.s_addr) {
        memcpy(&(preq_addr->s_addr), &bp->bp_ciaddr, 4);
    }
}

static void bootp_reply(Slirp *slirp,
                        const struct bootp_t *bp,
                        const uint8_t *bp_end)
{
    BOOTPClient *bc = NULL;
    struct mbuf *m;
    struct bootp_t *rbp;
    struct sockaddr_in saddr, daddr;
    struct in_addr preq_addr;
    int dhcp_msg_type, val;
    uint8_t *q;
    uint8_t *end;
    uint8_t client_ethaddr[ETH_ALEN];

    /* extract exact DHCP msg type */
    dhcp_decode(bp, bp_end, &dhcp_msg_type, &preq_addr);
    DPRINTF("bootp packet op=%d msgtype=%d", bp->bp_op, dhcp_msg_type);
    if (preq_addr.s_addr != htonl(0L))
        DPRINTF(" req_addr=%08" PRIx32 "\n", ntohl(preq_addr.s_addr));
    else {
        DPRINTF("\n");
    }

    if (dhcp_msg_type == 0)
        dhcp_msg_type = DHCPREQUEST; /* Force reply for old BOOTP clients */

    if (dhcp_msg_type != DHCPDISCOVER && dhcp_msg_type != DHCPREQUEST)
        return;

    /* Get client's hardware address from bootp request */
    memcpy(client_ethaddr, bp->bp_hwaddr, ETH_ALEN);

    m = m_get(slirp);
    if (!m) {
        return;
    }
    m->m_data += IF_MAXLINKHDR;
    m_inc(m, sizeof(struct bootp_t) + DHCP_OPT_LEN);
    rbp = (struct bootp_t *)m->m_data;
    m->m_data += sizeof(struct udpiphdr);
    memset(rbp, 0, sizeof(struct bootp_t) + DHCP_OPT_LEN);

    if (dhcp_msg_type == DHCPDISCOVER) {
        if (preq_addr.s_addr != htonl(0L)) {
            bc = request_addr(slirp, &preq_addr, client_ethaddr);
            if (bc) {
                daddr.sin_addr = preq_addr;
            }
        }
        if (!bc) {
        new_addr:
            bc = get_new_addr(slirp, &daddr.sin_addr, client_ethaddr);
            if (!bc) {
                DPRINTF("no address left\n");
                return;
            }
        }
        memcpy(bc->macaddr, client_ethaddr, ETH_ALEN);
    } else if (preq_addr.s_addr != htonl(0L)) {
        bc = request_addr(slirp, &preq_addr, client_ethaddr);
        if (bc) {
            daddr.sin_addr = preq_addr;
            memcpy(bc->macaddr, client_ethaddr, ETH_ALEN);
        } else {
            /* DHCPNAKs should be sent to broadcast */
            daddr.sin_addr.s_addr = 0xffffffff;
        }
    } else {
        bc = find_addr(slirp, &daddr.sin_addr, bp->bp_hwaddr);
        if (!bc) {
            /* if never assigned, behaves as if it was already
               assigned (windows fix because it remembers its address) */
            goto new_addr;
        }
    }

    /* Update ARP table for this IP address */
    arp_table_add(slirp, daddr.sin_addr.s_addr, client_ethaddr);

    saddr.sin_addr = slirp->vhost_addr;
    saddr.sin_port = htons(BOOTP_SERVER);

    daddr.sin_port = htons(BOOTP_CLIENT);

    rbp->bp_op = BOOTP_REPLY;
    rbp->bp_xid = bp->bp_xid;
    rbp->bp_htype = 1;
    rbp->bp_hlen = 6;
    memcpy(rbp->bp_hwaddr, bp->bp_hwaddr, ETH_ALEN);

    rbp->bp_yiaddr = daddr.sin_addr; /* Client IP address */
    rbp->bp_siaddr = saddr.sin_addr; /* Server IP address */

    q = rbp->bp_vend;
    end = rbp->bp_vend + DHCP_OPT_LEN;
    memcpy(q, rfc1533_cookie, 4);
    q += 4;

    if (bc) {
        DPRINTF("%s addr=%08" PRIx32 "\n",
                (dhcp_msg_type == DHCPDISCOVER) ? "offered" : "ack'ed",
                ntohl(daddr.sin_addr.s_addr));

        if (dhcp_msg_type == DHCPDISCOVER) {
            *q++ = RFC2132_MSG_TYPE;
            *q++ = 1;
            *q++ = DHCPOFFER;
        } else /* DHCPREQUEST */ {
            *q++ = RFC2132_MSG_TYPE;
            *q++ = 1;
            *q++ = DHCPACK;
        }

        if (slirp->bootp_filename) {
            g_assert(strlen(slirp->bootp_filename) < sizeof(rbp->bp_file));
            strcpy(rbp->bp_file, slirp->bootp_filename);
        }

        *q++ = RFC2132_SRV_ID;
        *q++ = 4;
        memcpy(q, &saddr.sin_addr, 4);
        q += 4;

        *q++ = RFC1533_NETMASK;
        *q++ = 4;
        memcpy(q, &slirp->vnetwork_mask, 4);
        q += 4;

        if (!slirp->restricted) {
            *q++ = RFC1533_GATEWAY;
            *q++ = 4;
            memcpy(q, &saddr.sin_addr, 4);
            q += 4;

            *q++ = RFC1533_DNS;
            *q++ = 4;
            memcpy(q, &slirp->vnameserver_addr, 4);
            q += 4;
        }

        *q++ = RFC2132_LEASE_TIME;
        *q++ = 4;
        val = htonl(LEASE_TIME);
        memcpy(q, &val, 4);
        q += 4;

        if (*slirp->client_hostname) {
            val = strlen(slirp->client_hostname);
            if (q + val + 2 >= end) {
                g_warning("DHCP packet size exceeded, "
                          "omitting host name option.");
            } else {
                *q++ = RFC1533_HOSTNAME;
                *q++ = val;
                memcpy(q, slirp->client_hostname, val);
                q += val;
            }
        }

        if (slirp->vdomainname) {
            val = strlen(slirp->vdomainname);
            if (q + val + 2 >= end) {
                g_warning("DHCP packet size exceeded, "
                          "omitting domain name option.");
            } else {
                *q++ = RFC1533_DOMAINNAME;
                *q++ = val;
                memcpy(q, slirp->vdomainname, val);
                q += val;
            }
        }

        if (slirp->tftp_server_name) {
            val = strlen(slirp->tftp_server_name);
            if (q + val + 2 >= end) {
                g_warning("DHCP packet size exceeded, "
                          "omitting tftp-server-name option.");
            } else {
                *q++ = RFC2132_TFTP_SERVER_NAME;
                *q++ = val;
                memcpy(q, slirp->tftp_server_name, val);
                q += val;
            }
        }

        if (slirp->vdnssearch) {
            val = slirp->vdnssearch_len;
            if (q + val >= end) {
                g_warning("DHCP packet size exceeded, "
                          "omitting domain-search option.");
            } else {
                memcpy(q, slirp->vdnssearch, val);
                q += val;
            }
        }
    } else {
        static const char nak_msg[] = "requested address not available";

        DPRINTF("nak'ed addr=%08" PRIx32 "\n", ntohl(preq_addr.s_addr));

        *q++ = RFC2132_MSG_TYPE;
        *q++ = 1;
        *q++ = DHCPNAK;

        *q++ = RFC2132_MESSAGE;
        *q++ = sizeof(nak_msg) - 1;
        memcpy(q, nak_msg, sizeof(nak_msg) - 1);
        q += sizeof(nak_msg) - 1;
    }
    assert(q < end);
    *q = RFC1533_END;

    daddr.sin_addr.s_addr = 0xffffffffu;

    m->m_len = sizeof(struct bootp_t) - sizeof(struct ip) - sizeof(struct udphdr);
    udp_output(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
}

void bootp_input(struct mbuf *m)
{
    struct bootp_t *bp = mtod_check(m, sizeof(struct bootp_t));

    if (bp && bp->bp_op == BOOTP_REQUEST) {
        bootp_reply(m->slirp, bp, m_end(m));
    }
}