tftp.c

/*
 * tftp.c - a simple, read-only tftp server for qemu
 *
 * Copyright (c) 2004 Magnus Damm <damm@opensource.se>
 *
 * 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>
#include "qemu-common.h" // for pstrcpy

struct tftp_session {
    int in_use;
    unsigned char filename[TFTP_FILENAME_MAX];

    struct in_addr client_ip;
    u_int16_t client_port;

    int timestamp;
};

static struct tftp_session tftp_sessions[TFTP_SESSIONS_MAX];

const char *tftp_prefix;

static void tftp_session_update(struct tftp_session *spt)
{
    spt->timestamp = curtime;
    spt->in_use = 1;
}

static void tftp_session_terminate(struct tftp_session *spt)
{
    spt->in_use = 0;
}

static int tftp_session_allocate(struct tftp_t *tp)
{
    struct tftp_session *spt;
    int k;

    for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
        spt = &tftp_sessions[k];

        if (!spt->in_use)
            goto found;

        /* sessions time out after 5 inactive seconds */
        if ((int)(curtime - spt->timestamp) > 5000)
            goto found;
    }

    return -1;

found:
    memset(spt, 0, sizeof(*spt));
    memcpy(&spt->client_ip, &tp->ip.ip_src, sizeof(spt->client_ip));
    spt->client_port = tp->udp.uh_sport;

    tftp_session_update(spt);

    return k;
}

static int tftp_session_find(struct tftp_t *tp)
{
    struct tftp_session *spt;
    int k;

    for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
        spt = &tftp_sessions[k];

        if (spt->in_use) {
            if (!memcmp(&spt->client_ip, &tp->ip.ip_src,
                        sizeof(spt->client_ip))) {
                if (spt->client_port == tp->udp.uh_sport) {
                    return k;
                }
            }
        }
    }

    return -1;
}

static int tftp_read_data(struct tftp_session *spt, u_int16_t block_nr,
                          u_int8_t *buf, int len)
{
    int fd;
    int bytes_read = 0;
    char buffer[1024];
    int n;

    n = snprintf(buffer, sizeof(buffer), "%s/%s", tftp_prefix, spt->filename);
    if (n >= sizeof(buffer))
        return -1;

    fd = open(buffer, O_RDONLY | O_BINARY);

    if (fd < 0) {
        return -1;
    }

    if (len) {
        lseek(fd, block_nr * 512, SEEK_SET);

        bytes_read = read(fd, buf, len);
    }

    close(fd);

    return bytes_read;
}

static int tftp_send_oack(struct tftp_session *spt, const char *key,
                          uint32_t value, struct tftp_t *recv_tp)
{
    struct sockaddr_in saddr, daddr;
    struct mbuf *m;
    struct tftp_t *tp;
    int n = 0;

    m = m_get();

    if (!m)
        return -1;

    memset(m->m_data, 0, m->m_size);

    m->m_data += IF_MAXLINKHDR;
    tp = (void *)m->m_data;
    m->m_data += sizeof(struct udpiphdr);

    tp->tp_op = htons(TFTP_OACK);
    n += snprintf((char *)tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%s",
                  key) +
         1;
    n += snprintf((char *)tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%u",
                  value) +
         1;

    saddr.sin_addr = recv_tp->ip.ip_dst;
    saddr.sin_port = recv_tp->udp.uh_dport;

    daddr.sin_addr = spt->client_ip;
    daddr.sin_port = spt->client_port;

    m->m_len = sizeof(struct tftp_t) - 514 + n - sizeof(struct ip) -
               sizeof(struct udphdr);
    udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);

    return 0;
}


static int tftp_send_error(struct tftp_session *spt, u_int16_t errorcode,
                           const char *msg, struct tftp_t *recv_tp)
{
    struct sockaddr_in saddr, daddr;
    struct mbuf *m;
    struct tftp_t *tp;
    int nobytes;

    m = m_get();

    if (!m) {
        return -1;
    }

    memset(m->m_data, 0, m->m_size);

    m->m_data += IF_MAXLINKHDR;
    tp = (void *)m->m_data;
    m->m_data += sizeof(struct udpiphdr);

    tp->tp_op = htons(TFTP_ERROR);
    tp->x.tp_error.tp_error_code = htons(errorcode);
    pstrcpy((char *)tp->x.tp_error.tp_msg, sizeof(tp->x.tp_error.tp_msg), msg);

    saddr.sin_addr = recv_tp->ip.ip_dst;
    saddr.sin_port = recv_tp->udp.uh_dport;

    daddr.sin_addr = spt->client_ip;
    daddr.sin_port = spt->client_port;

    nobytes = 2;

    m->m_len = sizeof(struct tftp_t) - 514 + 3 + strlen(msg) -
               sizeof(struct ip) - sizeof(struct udphdr);

    udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);

    tftp_session_terminate(spt);

    return 0;
}

static int tftp_send_data(struct tftp_session *spt, u_int16_t block_nr,
                          struct tftp_t *recv_tp)
{
    struct sockaddr_in saddr, daddr;
    struct mbuf *m;
    struct tftp_t *tp;
    int nobytes;

    if (block_nr < 1) {
        return -1;
    }

    m = m_get();

    if (!m) {
        return -1;
    }

    memset(m->m_data, 0, m->m_size);

    m->m_data += IF_MAXLINKHDR;
    tp = (void *)m->m_data;
    m->m_data += sizeof(struct udpiphdr);

    tp->tp_op = htons(TFTP_DATA);
    tp->x.tp_data.tp_block_nr = htons(block_nr);

    saddr.sin_addr = recv_tp->ip.ip_dst;
    saddr.sin_port = recv_tp->udp.uh_dport;

    daddr.sin_addr = spt->client_ip;
    daddr.sin_port = spt->client_port;

    nobytes = tftp_read_data(spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);

    if (nobytes < 0) {
        m_free(m);

        /* send "file not found" error back */

        tftp_send_error(spt, 1, "File not found", tp);

        return -1;
    }

    m->m_len = sizeof(struct tftp_t) - (512 - nobytes) - sizeof(struct ip) -
               sizeof(struct udphdr);

    udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);

    if (nobytes == 512) {
        tftp_session_update(spt);
    } else {
        tftp_session_terminate(spt);
    }

    return 0;
}

static void tftp_handle_rrq(struct tftp_t *tp, int pktlen)
{
    struct tftp_session *spt;
    int s, k, n;
    u_int8_t *src, *dst;

    s = tftp_session_allocate(tp);

    if (s < 0) {
        return;
    }

    spt = &tftp_sessions[s];

    src = tp->x.tp_buf;
    dst = spt->filename;
    n = pktlen - ((uint8_t *)&tp->x.tp_buf[0] - (uint8_t *)tp);

    /* get name */

    for (k = 0; k < n; k++) {
        if (k < TFTP_FILENAME_MAX) {
            dst[k] = src[k];
        } else {
            return;
        }

        if (src[k] == '\0') {
            break;
        }
    }

    if (k >= n) {
        return;
    }

    k++;

    /* check mode */
    if ((n - k) < 6) {
        return;
    }

    if (memcmp(&src[k], "octet\0", 6) != 0) {
        tftp_send_error(spt, 4, "Unsupported transfer mode", tp);
        return;
    }

    k += 6; /* skipping octet */

    /* do sanity checks on the filename */

    if ((spt->filename[0] != '/') ||
        (spt->filename[strlen((char *)spt->filename) - 1] == '/') ||
        strstr((char *)spt->filename, "/../")) {
        tftp_send_error(spt, 2, "Access violation", tp);
        return;
    }

    /* only allow exported prefixes */

    if (!tftp_prefix) {
        tftp_send_error(spt, 2, "Access violation", tp);
        return;
    }

    /* check if the file exists */

    if (tftp_read_data(spt, 0, spt->filename, 0) < 0) {
        tftp_send_error(spt, 1, "File not found", tp);
        return;
    }

    if (src[n - 1] != 0) {
        tftp_send_error(spt, 2, "Access violation", tp);
        return;
    }

    while (k < n) {
        const char *key, *value;

        key = (char *)src + k;
        k += strlen(key) + 1;

        if (k >= n) {
            tftp_send_error(spt, 2, "Access violation", tp);
            return;
        }

        value = (char *)src + k;
        k += strlen(value) + 1;

        if (strcmp(key, "tsize") == 0) {
            int tsize = atoi(value);
            struct stat stat_p;

            if (tsize == 0 && tftp_prefix) {
                char buffer[1024];
                int len;

                len = snprintf(buffer, sizeof(buffer), "%s/%s", tftp_prefix,
                               spt->filename);

                if (stat(buffer, &stat_p) == 0)
                    tsize = stat_p.st_size;
                else {
                    tftp_send_error(spt, 1, "File not found", tp);
                    return;
                }
            }

            tftp_send_oack(spt, "tsize", tsize, tp);
        }
    }

    tftp_send_data(spt, 1, tp);
}

static void tftp_handle_ack(struct tftp_t *tp, int pktlen)
{
    int s;

    s = tftp_session_find(tp);

    if (s < 0) {
        return;
    }

    if (tftp_send_data(&tftp_sessions[s], ntohs(tp->x.tp_data.tp_block_nr) + 1,
                       tp) < 0) {
        return;
    }
}

void tftp_input(struct mbuf *m)
{
    struct tftp_t *tp = (struct tftp_t *)m->m_data;

    switch (ntohs(tp->tp_op)) {
    case TFTP_RRQ:
        tftp_handle_rrq(tp, m->m_len);
        break;

    case TFTP_ACK:
        tftp_handle_ack(tp, m->m_len);
        break;
    }
}