xref: /netbsd-src/crypto/external/bsd/openssl.old/dist/ssl/d1_lib.c (revision 4724848cf0da353df257f730694b7882798e5daf)

/*
 * Copyright 2005-2021 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#include "e_os.h"
#include <stdio.h>
#include <openssl/objects.h>
#include <openssl/rand.h>
#include "ssl_local.h"

static void get_current_time(struct timeval *t);
static int dtls1_handshake_write(SSL *s);
static size_t dtls1_link_min_mtu(void);

/* XDTLS:  figure out the right values */
static const size_t g_probable_mtu[] = { 1500, 512, 256 };

const SSL3_ENC_METHOD DTLSv1_enc_data = {
    tls1_enc,
    tls1_mac,
    tls1_setup_key_block,
    tls1_generate_master_secret,
    tls1_change_cipher_state,
    tls1_final_finish_mac,
    TLS_MD_CLIENT_FINISH_CONST, TLS_MD_CLIENT_FINISH_CONST_SIZE,
    TLS_MD_SERVER_FINISH_CONST, TLS_MD_SERVER_FINISH_CONST_SIZE,
    tls1_alert_code,
    tls1_export_keying_material,
    SSL_ENC_FLAG_DTLS | SSL_ENC_FLAG_EXPLICIT_IV,
    dtls1_set_handshake_header,
    dtls1_close_construct_packet,
    dtls1_handshake_write
};

const SSL3_ENC_METHOD DTLSv1_2_enc_data = {
    tls1_enc,
    tls1_mac,
    tls1_setup_key_block,
    tls1_generate_master_secret,
    tls1_change_cipher_state,
    tls1_final_finish_mac,
    TLS_MD_CLIENT_FINISH_CONST, TLS_MD_CLIENT_FINISH_CONST_SIZE,
    TLS_MD_SERVER_FINISH_CONST, TLS_MD_SERVER_FINISH_CONST_SIZE,
    tls1_alert_code,
    tls1_export_keying_material,
    SSL_ENC_FLAG_DTLS | SSL_ENC_FLAG_EXPLICIT_IV | SSL_ENC_FLAG_SIGALGS
        | SSL_ENC_FLAG_SHA256_PRF | SSL_ENC_FLAG_TLS1_2_CIPHERS,
    dtls1_set_handshake_header,
    dtls1_close_construct_packet,
    dtls1_handshake_write
};

long dtls1_default_timeout(void)
{
    /*
     * 2 hours, the 24 hours mentioned in the DTLSv1 spec is way too long for
     * http, the cache would over fill
     */
    return (60 * 60 * 2);
}

int dtls1_new(SSL *s)
{
    DTLS1_STATE *d1;

    if (!DTLS_RECORD_LAYER_new(&s->rlayer)) {
        return 0;
    }

    if (!ssl3_new(s))
        return 0;
    if ((d1 = OPENSSL_zalloc(sizeof(*d1))) == NULL) {
        ssl3_free(s);
        return 0;
    }

    d1->buffered_messages = pqueue_new();
    d1->sent_messages = pqueue_new();

    if (s->server) {
        d1->cookie_len = sizeof(s->d1->cookie);
    }

    d1->link_mtu = 0;
    d1->mtu = 0;

    if (d1->buffered_messages == NULL || d1->sent_messages == NULL) {
        pqueue_free(d1->buffered_messages);
        pqueue_free(d1->sent_messages);
        OPENSSL_free(d1);
        ssl3_free(s);
        return 0;
    }

    s->d1 = d1;

    if (!s->method->ssl_clear(s))
        return 0;

    return 1;
}

static void dtls1_clear_queues(SSL *s)
{
    dtls1_clear_received_buffer(s);
    dtls1_clear_sent_buffer(s);
}

void dtls1_clear_received_buffer(SSL *s)
{
    pitem *item = NULL;
    hm_fragment *frag = NULL;

    while ((item = pqueue_pop(s->d1->buffered_messages)) != NULL) {
        frag = (hm_fragment *)item->data;
        dtls1_hm_fragment_free(frag);
        pitem_free(item);
    }
}

void dtls1_clear_sent_buffer(SSL *s)
{
    pitem *item = NULL;
    hm_fragment *frag = NULL;

    while ((item = pqueue_pop(s->d1->sent_messages)) != NULL) {
        frag = (hm_fragment *)item->data;
        dtls1_hm_fragment_free(frag);
        pitem_free(item);
    }
}


void dtls1_free(SSL *s)
{
    DTLS_RECORD_LAYER_free(&s->rlayer);

    ssl3_free(s);

    if (s->d1 != NULL) {
        dtls1_clear_queues(s);
        pqueue_free(s->d1->buffered_messages);
        pqueue_free(s->d1->sent_messages);
    }

    OPENSSL_free(s->d1);
    s->d1 = NULL;
}

int dtls1_clear(SSL *s)
{
    pqueue *buffered_messages;
    pqueue *sent_messages;
    size_t mtu;
    size_t link_mtu;

    DTLS_RECORD_LAYER_clear(&s->rlayer);

    if (s->d1) {
        DTLS_timer_cb timer_cb = s->d1->timer_cb;

        buffered_messages = s->d1->buffered_messages;
        sent_messages = s->d1->sent_messages;
        mtu = s->d1->mtu;
        link_mtu = s->d1->link_mtu;

        dtls1_clear_queues(s);

        memset(s->d1, 0, sizeof(*s->d1));

        /* Restore the timer callback from previous state */
        s->d1->timer_cb = timer_cb;

        if (s->server) {
            s->d1->cookie_len = sizeof(s->d1->cookie);
        }

        if (SSL_get_options(s) & SSL_OP_NO_QUERY_MTU) {
            s->d1->mtu = mtu;
            s->d1->link_mtu = link_mtu;
        }

        s->d1->buffered_messages = buffered_messages;
        s->d1->sent_messages = sent_messages;
    }

    if (!ssl3_clear(s))
        return 0;

    if (s->method->version == DTLS_ANY_VERSION)
        s->version = DTLS_MAX_VERSION;
#ifndef OPENSSL_NO_DTLS1_METHOD
    else if (s->options & SSL_OP_CISCO_ANYCONNECT)
        s->client_version = s->version = DTLS1_BAD_VER;
#endif
    else
        s->version = s->method->version;

    return 1;
}

long dtls1_ctrl(SSL *s, int cmd, long larg, void *parg)
{
    int ret = 0;

    switch (cmd) {
    case DTLS_CTRL_GET_TIMEOUT:
        if (dtls1_get_timeout(s, (struct timeval *)parg) != NULL) {
            ret = 1;
        }
        break;
    case DTLS_CTRL_HANDLE_TIMEOUT:
        ret = dtls1_handle_timeout(s);
        break;
    case DTLS_CTRL_SET_LINK_MTU:
        if (larg < (long)dtls1_link_min_mtu())
            return 0;
        s->d1->link_mtu = larg;
        return 1;
    case DTLS_CTRL_GET_LINK_MIN_MTU:
        return (long)dtls1_link_min_mtu();
    case SSL_CTRL_SET_MTU:
        /*
         *  We may not have a BIO set yet so can't call dtls1_min_mtu()
         *  We'll have to make do with dtls1_link_min_mtu() and max overhead
         */
        if (larg < (long)dtls1_link_min_mtu() - DTLS1_MAX_MTU_OVERHEAD)
            return 0;
        s->d1->mtu = larg;
        return larg;
    default:
        ret = ssl3_ctrl(s, cmd, larg, parg);
        break;
    }
    return ret;
}

void dtls1_start_timer(SSL *s)
{
    unsigned int sec, usec;

#ifndef OPENSSL_NO_SCTP
    /* Disable timer for SCTP */
    if (BIO_dgram_is_sctp(SSL_get_wbio(s))) {
        memset(&s->d1->next_timeout, 0, sizeof(s->d1->next_timeout));
        return;
    }
#endif

    /*
     * If timer is not set, initialize duration with 1 second or
     * a user-specified value if the timer callback is installed.
     */
    if (s->d1->next_timeout.tv_sec == 0 && s->d1->next_timeout.tv_usec == 0) {

        if (s->d1->timer_cb != NULL)
            s->d1->timeout_duration_us = s->d1->timer_cb(s, 0);
        else
            s->d1->timeout_duration_us = 1000000;
    }

    /* Set timeout to current time */
    get_current_time(&(s->d1->next_timeout));

    /* Add duration to current time */

    sec  = s->d1->timeout_duration_us / 1000000;
    usec = s->d1->timeout_duration_us - (sec * 1000000);

    s->d1->next_timeout.tv_sec  += sec;
    s->d1->next_timeout.tv_usec += usec;

    if (s->d1->next_timeout.tv_usec >= 1000000) {
        s->d1->next_timeout.tv_sec++;
        s->d1->next_timeout.tv_usec -= 1000000;
    }

    BIO_ctrl(SSL_get_rbio(s), BIO_CTRL_DGRAM_SET_NEXT_TIMEOUT, 0,
             &(s->d1->next_timeout));
}

struct timeval *dtls1_get_timeout(SSL *s, struct timeval *timeleft)
{
    struct timeval timenow;

    /* If no timeout is set, just return NULL */
    if (s->d1->next_timeout.tv_sec == 0 && s->d1->next_timeout.tv_usec == 0) {
        return NULL;
    }

    /* Get current time */
    get_current_time(&timenow);

    /* If timer already expired, set remaining time to 0 */
    if (s->d1->next_timeout.tv_sec < timenow.tv_sec ||
        (s->d1->next_timeout.tv_sec == timenow.tv_sec &&
         s->d1->next_timeout.tv_usec <= timenow.tv_usec)) {
        memset(timeleft, 0, sizeof(*timeleft));
        return timeleft;
    }

    /* Calculate time left until timer expires */
    memcpy(timeleft, &(s->d1->next_timeout), sizeof(struct timeval));
    timeleft->tv_sec -= timenow.tv_sec;
    timeleft->tv_usec -= timenow.tv_usec;
    if (timeleft->tv_usec < 0) {
        timeleft->tv_sec--;
        timeleft->tv_usec += 1000000;
    }

    /*
     * If remaining time is less than 15 ms, set it to 0 to prevent issues
     * because of small divergences with socket timeouts.
     */
    if (timeleft->tv_sec == 0 && timeleft->tv_usec < 15000) {
        memset(timeleft, 0, sizeof(*timeleft));
    }

    return timeleft;
}

int dtls1_is_timer_expired(SSL *s)
{
    struct timeval timeleft;

    /* Get time left until timeout, return false if no timer running */
    if (dtls1_get_timeout(s, &timeleft) == NULL) {
        return 0;
    }

    /* Return false if timer is not expired yet */
    if (timeleft.tv_sec > 0 || timeleft.tv_usec > 0) {
        return 0;
    }

    /* Timer expired, so return true */
    return 1;
}

static void dtls1_double_timeout(SSL *s)
{
    s->d1->timeout_duration_us *= 2;
    if (s->d1->timeout_duration_us > 60000000)
        s->d1->timeout_duration_us = 60000000;
}

void dtls1_stop_timer(SSL *s)
{
    /* Reset everything */
    memset(&s->d1->timeout, 0, sizeof(s->d1->timeout));
    memset(&s->d1->next_timeout, 0, sizeof(s->d1->next_timeout));
    s->d1->timeout_duration_us = 1000000;
    BIO_ctrl(SSL_get_rbio(s), BIO_CTRL_DGRAM_SET_NEXT_TIMEOUT, 0,
             &(s->d1->next_timeout));
    /* Clear retransmission buffer */
    dtls1_clear_sent_buffer(s);
}

int dtls1_check_timeout_num(SSL *s)
{
    size_t mtu;

    s->d1->timeout.num_alerts++;

    /* Reduce MTU after 2 unsuccessful retransmissions */
    if (s->d1->timeout.num_alerts > 2
        && !(SSL_get_options(s) & SSL_OP_NO_QUERY_MTU)) {
        mtu =
            BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_GET_FALLBACK_MTU, 0, NULL);
        if (mtu < s->d1->mtu)
            s->d1->mtu = mtu;
    }

    if (s->d1->timeout.num_alerts > DTLS1_TMO_ALERT_COUNT) {
        /* fail the connection, enough alerts have been sent */
        SSLfatal(s, SSL_AD_NO_ALERT, SSL_F_DTLS1_CHECK_TIMEOUT_NUM,
                 SSL_R_READ_TIMEOUT_EXPIRED);
        return -1;
    }

    return 0;
}

int dtls1_handle_timeout(SSL *s)
{
    /* if no timer is expired, don't do anything */
    if (!dtls1_is_timer_expired(s)) {
        return 0;
    }

    if (s->d1->timer_cb != NULL)
        s->d1->timeout_duration_us = s->d1->timer_cb(s, s->d1->timeout_duration_us);
    else
        dtls1_double_timeout(s);

    if (dtls1_check_timeout_num(s) < 0) {
        /* SSLfatal() already called */
        return -1;
    }

    s->d1->timeout.read_timeouts++;
    if (s->d1->timeout.read_timeouts > DTLS1_TMO_READ_COUNT) {
        s->d1->timeout.read_timeouts = 1;
    }

    dtls1_start_timer(s);
    /* Calls SSLfatal() if required */
    return dtls1_retransmit_buffered_messages(s);
}

static void get_current_time(struct timeval *t)
{
#if defined(_WIN32)
    SYSTEMTIME st;
    union {
        unsigned __int64 ul;
        FILETIME ft;
    } now;

    GetSystemTime(&st);
    SystemTimeToFileTime(&st, &now.ft);
    /* re-bias to 1/1/1970 */
# ifdef  __MINGW32__
    now.ul -= 116444736000000000ULL;
# else
    /* *INDENT-OFF* */
    now.ul -= 116444736000000000UI64;
    /* *INDENT-ON* */
# endif
    t->tv_sec = (long)(now.ul / 10000000);
    t->tv_usec = ((int)(now.ul % 10000000)) / 10;
#else
    gettimeofday(t, NULL);
#endif
}

#define LISTEN_SUCCESS              2
#define LISTEN_SEND_VERIFY_REQUEST  1

#ifndef OPENSSL_NO_SOCK
int DTLSv1_listen(SSL *s, BIO_ADDR *client)
{
    int next, n, ret = 0;
    unsigned char cookie[DTLS1_COOKIE_LENGTH];
    unsigned char seq[SEQ_NUM_SIZE];
    const unsigned char *data;
    unsigned char *buf, *wbuf;
    size_t fragoff, fraglen, msglen, reclen, align = 0;
    unsigned int rectype, versmajor, msgseq, msgtype, clientvers, cookielen;
    BIO *rbio, *wbio;
    BIO_ADDR *tmpclient = NULL;
    PACKET pkt, msgpkt, msgpayload, session, cookiepkt;

    if (s->handshake_func == NULL) {
        /* Not properly initialized yet */
        SSL_set_accept_state(s);
    }

    /* Ensure there is no state left over from a previous invocation */
    if (!SSL_clear(s))
        return -1;

    ERR_clear_error();

    rbio = SSL_get_rbio(s);
    wbio = SSL_get_wbio(s);

    if (!rbio || !wbio) {
        SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_BIO_NOT_SET);
        return -1;
    }

    /*
     * Note: This check deliberately excludes DTLS1_BAD_VER because that version
     * requires the MAC to be calculated *including* the first ClientHello
     * (without the cookie). Since DTLSv1_listen is stateless that cannot be
     * supported. DTLS1_BAD_VER must use cookies in a stateful manner (e.g. via
     * SSL_accept)
     */
    if ((s->version & 0xff00) != (DTLS1_VERSION & 0xff00)) {
        SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_UNSUPPORTED_SSL_VERSION);
        return -1;
    }

    if (!ssl3_setup_buffers(s)) {
        /* SSLerr already called */
        return -1;
    }
    buf = RECORD_LAYER_get_rbuf(&s->rlayer)->buf;
    wbuf = RECORD_LAYER_get_wbuf(&s->rlayer)[0].buf;
#if defined(SSL3_ALIGN_PAYLOAD)
# if SSL3_ALIGN_PAYLOAD != 0
    /*
     * Using SSL3_RT_HEADER_LENGTH here instead of DTLS1_RT_HEADER_LENGTH for
     * consistency with ssl3_read_n. In practice it should make no difference
     * for sensible values of SSL3_ALIGN_PAYLOAD because the difference between
     * SSL3_RT_HEADER_LENGTH and DTLS1_RT_HEADER_LENGTH is exactly 8
     */
    align = (size_t)buf + SSL3_RT_HEADER_LENGTH;
    align = SSL3_ALIGN_PAYLOAD - 1 - ((align - 1) % SSL3_ALIGN_PAYLOAD);
# endif
#endif
    buf += align;

    do {
        /* Get a packet */

        clear_sys_error();
        n = BIO_read(rbio, buf, SSL3_RT_MAX_PLAIN_LENGTH
                                + DTLS1_RT_HEADER_LENGTH);
        if (n <= 0) {
            if (BIO_should_retry(rbio)) {
                /* Non-blocking IO */
                goto end;
            }
            return -1;
        }

        if (!PACKET_buf_init(&pkt, buf, n)) {
            SSLerr(SSL_F_DTLSV1_LISTEN, ERR_R_INTERNAL_ERROR);
            return -1;
        }

        /*
         * Parse the received record. If there are any problems with it we just
         * dump it - with no alert. RFC6347 says this "Unlike TLS, DTLS is
         * resilient in the face of invalid records (e.g., invalid formatting,
         * length, MAC, etc.).  In general, invalid records SHOULD be silently
         * discarded, thus preserving the association; however, an error MAY be
         * logged for diagnostic purposes."
         */

        /* this packet contained a partial record, dump it */
        if (n < DTLS1_RT_HEADER_LENGTH) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_RECORD_TOO_SMALL);
            goto end;
        }

        if (s->msg_callback)
            s->msg_callback(0, 0, SSL3_RT_HEADER, buf,
                            DTLS1_RT_HEADER_LENGTH, s, s->msg_callback_arg);

        /* Get the record header */
        if (!PACKET_get_1(&pkt, &rectype)
            || !PACKET_get_1(&pkt, &versmajor)) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_LENGTH_MISMATCH);
            goto end;
        }

        if (rectype != SSL3_RT_HANDSHAKE) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_UNEXPECTED_MESSAGE);
            goto end;
        }

        /*
         * Check record version number. We only check that the major version is
         * the same.
         */
        if (versmajor != DTLS1_VERSION_MAJOR) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_BAD_PROTOCOL_VERSION_NUMBER);
            goto end;
        }

        if (!PACKET_forward(&pkt, 1)
            /* Save the sequence number: 64 bits, with top 2 bytes = epoch */
            || !PACKET_copy_bytes(&pkt, seq, SEQ_NUM_SIZE)
            || !PACKET_get_length_prefixed_2(&pkt, &msgpkt)) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_LENGTH_MISMATCH);
            goto end;
        }
        reclen = PACKET_remaining(&msgpkt);
        /*
         * We allow data remaining at the end of the packet because there could
         * be a second record (but we ignore it)
         */

        /* This is an initial ClientHello so the epoch has to be 0 */
        if (seq[0] != 0 || seq[1] != 0) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_UNEXPECTED_MESSAGE);
            goto end;
        }

        /* Get a pointer to the raw message for the later callback */
        data = PACKET_data(&msgpkt);

        /* Finished processing the record header, now process the message */
        if (!PACKET_get_1(&msgpkt, &msgtype)
            || !PACKET_get_net_3_len(&msgpkt, &msglen)
            || !PACKET_get_net_2(&msgpkt, &msgseq)
            || !PACKET_get_net_3_len(&msgpkt, &fragoff)
            || !PACKET_get_net_3_len(&msgpkt, &fraglen)
            || !PACKET_get_sub_packet(&msgpkt, &msgpayload, fraglen)
            || PACKET_remaining(&msgpkt) != 0) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_LENGTH_MISMATCH);
            goto end;
        }

        if (msgtype != SSL3_MT_CLIENT_HELLO) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_UNEXPECTED_MESSAGE);
            goto end;
        }

        /* Message sequence number can only be 0 or 1 */
        if (msgseq > 2) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_INVALID_SEQUENCE_NUMBER);
            goto end;
        }

        /*
         * We don't support fragment reassembly for ClientHellos whilst
         * listening because that would require server side state (which is
         * against the whole point of the ClientHello/HelloVerifyRequest
         * mechanism). Instead we only look at the first ClientHello fragment
         * and require that the cookie must be contained within it.
         */
        if (fragoff != 0 || fraglen > msglen) {
            /* Non initial ClientHello fragment (or bad fragment) */
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_FRAGMENTED_CLIENT_HELLO);
            goto end;
        }

        if (s->msg_callback)
            s->msg_callback(0, s->version, SSL3_RT_HANDSHAKE, data,
                            fraglen + DTLS1_HM_HEADER_LENGTH, s,
                            s->msg_callback_arg);

        if (!PACKET_get_net_2(&msgpayload, &clientvers)) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_LENGTH_MISMATCH);
            goto end;
        }

        /*
         * Verify client version is supported
         */
        if (DTLS_VERSION_LT(clientvers, (unsigned int)s->method->version) &&
            s->method->version != DTLS_ANY_VERSION) {
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_WRONG_VERSION_NUMBER);
            goto end;
        }

        if (!PACKET_forward(&msgpayload, SSL3_RANDOM_SIZE)
            || !PACKET_get_length_prefixed_1(&msgpayload, &session)
            || !PACKET_get_length_prefixed_1(&msgpayload, &cookiepkt)) {
            /*
             * Could be malformed or the cookie does not fit within the initial
             * ClientHello fragment. Either way we can't handle it.
             */
            SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_LENGTH_MISMATCH);
            goto end;
        }

        /*
         * Check if we have a cookie or not. If not we need to send a
         * HelloVerifyRequest.
         */
        if (PACKET_remaining(&cookiepkt) == 0) {
            next = LISTEN_SEND_VERIFY_REQUEST;
        } else {
            /*
             * We have a cookie, so lets check it.
             */
            if (s->ctx->app_verify_cookie_cb == NULL) {
                SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_NO_VERIFY_COOKIE_CALLBACK);
                /* This is fatal */
                return -1;
            }
            if (s->ctx->app_verify_cookie_cb(s, PACKET_data(&cookiepkt),
                    (unsigned int)PACKET_remaining(&cookiepkt)) == 0) {
                /*
                 * We treat invalid cookies in the same was as no cookie as
                 * per RFC6347
                 */
                next = LISTEN_SEND_VERIFY_REQUEST;
            } else {
                /* Cookie verification succeeded */
                next = LISTEN_SUCCESS;
            }
        }

        if (next == LISTEN_SEND_VERIFY_REQUEST) {
            WPACKET wpkt;
            unsigned int version;
            size_t wreclen;

            /*
             * There was no cookie in the ClientHello so we need to send a
             * HelloVerifyRequest. If this fails we do not worry about trying
             * to resend, we just drop it.
             */

            /* Generate the cookie */
            if (s->ctx->app_gen_cookie_cb == NULL ||
                s->ctx->app_gen_cookie_cb(s, cookie, &cookielen) == 0 ||
                cookielen > 255) {
                SSLerr(SSL_F_DTLSV1_LISTEN, SSL_R_COOKIE_GEN_CALLBACK_FAILURE);
                /* This is fatal */
                return -1;
            }

            /*
             * Special case: for hello verify request, client version 1.0 and we
             * haven't decided which version to use yet send back using version
             * 1.0 header: otherwise some clients will ignore it.
             */
            version = (s->method->version == DTLS_ANY_VERSION) ? DTLS1_VERSION
                                                               : s->version;

            /* Construct the record and message headers */
            if (!WPACKET_init_static_len(&wpkt,
                                         wbuf,
                                         ssl_get_max_send_fragment(s)
                                         + DTLS1_RT_HEADER_LENGTH,
                                         0)
                    || !WPACKET_put_bytes_u8(&wpkt, SSL3_RT_HANDSHAKE)
                    || !WPACKET_put_bytes_u16(&wpkt, version)
                       /*
                        * Record sequence number is always the same as in the
                        * received ClientHello
                        */
                    || !WPACKET_memcpy(&wpkt, seq, SEQ_NUM_SIZE)
                       /* End of record, start sub packet for message */
                    || !WPACKET_start_sub_packet_u16(&wpkt)
                       /* Message type */
                    || !WPACKET_put_bytes_u8(&wpkt,
                                             DTLS1_MT_HELLO_VERIFY_REQUEST)
                       /*
                        * Message length - doesn't follow normal TLS convention:
                        * the length isn't the last thing in the message header.
                        * We'll need to fill this in later when we know the
                        * length. Set it to zero for now
                        */
                    || !WPACKET_put_bytes_u24(&wpkt, 0)
                       /*
                        * Message sequence number is always 0 for a
                        * HelloVerifyRequest
                        */
                    || !WPACKET_put_bytes_u16(&wpkt, 0)
                       /*
                        * We never fragment a HelloVerifyRequest, so fragment
                        * offset is 0
                        */
                    || !WPACKET_put_bytes_u24(&wpkt, 0)
                       /*
                        * Fragment length is the same as message length, but
                        * this *is* the last thing in the message header so we
                        * can just start a sub-packet. No need to come back
                        * later for this one.
                        */
                    || !WPACKET_start_sub_packet_u24(&wpkt)
                       /* Create the actual HelloVerifyRequest body */
                    || !dtls_raw_hello_verify_request(&wpkt, cookie, cookielen)
                       /* Close message body */
                    || !WPACKET_close(&wpkt)
                       /* Close record body */
                    || !WPACKET_close(&wpkt)
                    || !WPACKET_get_total_written(&wpkt, &wreclen)
                    || !WPACKET_finish(&wpkt)) {
                SSLerr(SSL_F_DTLSV1_LISTEN, ERR_R_INTERNAL_ERROR);
                WPACKET_cleanup(&wpkt);
                /* This is fatal */
                return -1;
            }

            /*
             * Fix up the message len in the message header. Its the same as the
             * fragment len which has been filled in by WPACKET, so just copy
             * that. Destination for the message len is after the record header
             * plus one byte for the message content type. The source is the
             * last 3 bytes of the message header
             */
            memcpy(&wbuf[DTLS1_RT_HEADER_LENGTH + 1],
                   &wbuf[DTLS1_RT_HEADER_LENGTH + DTLS1_HM_HEADER_LENGTH - 3],
                   3);

            if (s->msg_callback)
                s->msg_callback(1, 0, SSL3_RT_HEADER, buf,
                                DTLS1_RT_HEADER_LENGTH, s, s->msg_callback_arg);

            if ((tmpclient = BIO_ADDR_new()) == NULL) {
                SSLerr(SSL_F_DTLSV1_LISTEN, ERR_R_MALLOC_FAILURE);
                goto end;
            }

            /*
             * This is unnecessary if rbio and wbio are one and the same - but
             * maybe they're not. We ignore errors here - some BIOs do not
             * support this.
             */
            if (BIO_dgram_get_peer(rbio, tmpclient) > 0) {
                (void)BIO_dgram_set_peer(wbio, tmpclient);
            }
            BIO_ADDR_free(tmpclient);
            tmpclient = NULL;

            /* TODO(size_t): convert this call */
            if (BIO_write(wbio, wbuf, wreclen) < (int)wreclen) {
                if (BIO_should_retry(wbio)) {
                    /*
                     * Non-blocking IO...but we're stateless, so we're just
                     * going to drop this packet.
                     */
                    goto end;
                }
                return -1;
            }

            if (BIO_flush(wbio) <= 0) {
                if (BIO_should_retry(wbio)) {
                    /*
                     * Non-blocking IO...but we're stateless, so we're just
                     * going to drop this packet.
                     */
                    goto end;
                }
                return -1;
            }
        }
    } while (next != LISTEN_SUCCESS);

    /*
     * Set expected sequence numbers to continue the handshake.
     */
    s->d1->handshake_read_seq = 1;
    s->d1->handshake_write_seq = 1;
    s->d1->next_handshake_write_seq = 1;
    DTLS_RECORD_LAYER_set_write_sequence(&s->rlayer, seq);

    /*
     * We are doing cookie exchange, so make sure we set that option in the
     * SSL object
     */
    SSL_set_options(s, SSL_OP_COOKIE_EXCHANGE);

    /*
     * Tell the state machine that we've done the initial hello verify
     * exchange
     */
    ossl_statem_set_hello_verify_done(s);

    /*
     * Some BIOs may not support this. If we fail we clear the client address
     */
    if (BIO_dgram_get_peer(rbio, client) <= 0)
        BIO_ADDR_clear(client);

    /* Buffer the record in the processed_rcds queue */
    if (!dtls_buffer_listen_record(s, reclen, seq, align))
        return -1;

    ret = 1;
 end:
    BIO_ADDR_free(tmpclient);
    return ret;
}
#endif

static int dtls1_handshake_write(SSL *s)
{
    return dtls1_do_write(s, SSL3_RT_HANDSHAKE);
}

int dtls1_shutdown(SSL *s)
{
    int ret;
#ifndef OPENSSL_NO_SCTP
    BIO *wbio;

    wbio = SSL_get_wbio(s);
    if (wbio != NULL && BIO_dgram_is_sctp(wbio) &&
        !(s->shutdown & SSL_SENT_SHUTDOWN)) {
        ret = BIO_dgram_sctp_wait_for_dry(wbio);
        if (ret < 0)
            return -1;

        if (ret == 0)
            BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_SCTP_SAVE_SHUTDOWN, 1,
                     NULL);
    }
#endif
    ret = ssl3_shutdown(s);
#ifndef OPENSSL_NO_SCTP
    BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_SCTP_SAVE_SHUTDOWN, 0, NULL);
#endif
    return ret;
}

int dtls1_query_mtu(SSL *s)
{
    if (s->d1->link_mtu) {
        s->d1->mtu =
            s->d1->link_mtu - BIO_dgram_get_mtu_overhead(SSL_get_wbio(s));
        s->d1->link_mtu = 0;
    }

    /* AHA!  Figure out the MTU, and stick to the right size */
    if (s->d1->mtu < dtls1_min_mtu(s)) {
        if (!(SSL_get_options(s) & SSL_OP_NO_QUERY_MTU)) {
            s->d1->mtu =
                BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_QUERY_MTU, 0, NULL);

            /*
             * I've seen the kernel return bogus numbers when it doesn't know
             * (initial write), so just make sure we have a reasonable number
             */
            if (s->d1->mtu < dtls1_min_mtu(s)) {
                /* Set to min mtu */
                s->d1->mtu = dtls1_min_mtu(s);
                BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_SET_MTU,
                         (long)s->d1->mtu, NULL);
            }
        } else
            return 0;
    }
    return 1;
}

static size_t dtls1_link_min_mtu(void)
{
    return (g_probable_mtu[(sizeof(g_probable_mtu) /
                            sizeof(g_probable_mtu[0])) - 1]);
}

size_t dtls1_min_mtu(SSL *s)
{
    return dtls1_link_min_mtu() - BIO_dgram_get_mtu_overhead(SSL_get_wbio(s));
}

size_t DTLS_get_data_mtu(const SSL *s)
{
    size_t mac_overhead, int_overhead, blocksize, ext_overhead;
    const SSL_CIPHER *ciph = SSL_get_current_cipher(s);
    size_t mtu = s->d1->mtu;

    if (ciph == NULL)
        return 0;

    if (!ssl_cipher_get_overhead(ciph, &mac_overhead, &int_overhead,
                                 &blocksize, &ext_overhead))
        return 0;

    if (SSL_READ_ETM(s))
        ext_overhead += mac_overhead;
    else
        int_overhead += mac_overhead;

    /* Subtract external overhead (e.g. IV/nonce, separate MAC) */
    if (ext_overhead + DTLS1_RT_HEADER_LENGTH >= mtu)
        return 0;
    mtu -= ext_overhead + DTLS1_RT_HEADER_LENGTH;

    /* Round encrypted payload down to cipher block size (for CBC etc.)
     * No check for overflow since 'mtu % blocksize' cannot exceed mtu. */
    if (blocksize)
        mtu -= (mtu % blocksize);

    /* Subtract internal overhead (e.g. CBC padding len byte) */
    if (int_overhead >= mtu)
        return 0;
    mtu -= int_overhead;

    return mtu;
}

void DTLS_set_timer_cb(SSL *s, DTLS_timer_cb cb)
{
    s->d1->timer_cb = cb;
}