int ssl3_accept(SSL *s)
{
    BUF_MEM *buf;
    unsigned long alg_k, Time = (unsigned long)time(NULL);
    void (*cb) (const SSL *ssl, int type, int val) = NULL;
    int ret = -1;
    int new_state, state, skip = 0;

    RAND_add(&Time, sizeof(Time), 0);
    ERR_clear_error();
    clear_sys_error();

    if (s->info_callback != NULL)
        cb = s->info_callback;
    else if (s->ctx->info_callback != NULL)
        cb = s->ctx->info_callback;

    /* init things to blank */
    s->in_handshake++;
    if (!SSL_in_init(s) || SSL_in_before(s))
        SSL_clear(s);

    if (s->cert == NULL) {
        SSLerr(SSL_F_SSL3_ACCEPT, SSL_R_NO_CERTIFICATE_SET);
        return (-1);
    }
#ifndef OPENSSL_NO_HEARTBEATS
    /*
     * If we're awaiting a HeartbeatResponse, pretend we already got and
     * don't await it anymore, because Heartbeats don't make sense during
     * handshakes anyway.
     */
    if (s->tlsext_hb_pending) {
        s->tlsext_hb_pending = 0;
        s->tlsext_hb_seq++;
    }
#endif

    for (;;) {
        state = s->state;

        switch (s->state) {
        case SSL_ST_RENEGOTIATE:
            s->renegotiate = 1;
            /* s->state=SSL_ST_ACCEPT; */

        case SSL_ST_BEFORE:
        case SSL_ST_ACCEPT:
        case SSL_ST_BEFORE | SSL_ST_ACCEPT:
        case SSL_ST_OK | SSL_ST_ACCEPT:

            s->server = 1;
            if (cb != NULL)
                cb(s, SSL_CB_HANDSHAKE_START, 1);

            if ((s->version >> 8) != 3) {
                SSLerr(SSL_F_SSL3_ACCEPT, ERR_R_INTERNAL_ERROR);
                s->state = SSL_ST_ERR;
                return -1;
            }
            s->type = SSL_ST_ACCEPT;

            if (s->init_buf == NULL) {
                if ((buf = BUF_MEM_new()) == NULL) {
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }
                if (!BUF_MEM_grow(buf, SSL3_RT_MAX_PLAIN_LENGTH)) {
                    BUF_MEM_free(buf);
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }
                s->init_buf = buf;
            }

            if (!ssl3_setup_buffers(s)) {
                ret = -1;
                s->state = SSL_ST_ERR;
                goto end;
            }

            s->init_num = 0;
            s->s3->flags &= ~TLS1_FLAGS_SKIP_CERT_VERIFY;
            s->s3->flags &= ~SSL3_FLAGS_CCS_OK;
            /*
             * Should have been reset by ssl3_get_finished, too.
             */
            s->s3->change_cipher_spec = 0;

            if (s->state != SSL_ST_RENEGOTIATE) {
                /*
                 * Ok, we now need to push on a buffering BIO so that the
                 * output is sent in a way that TCP likes :-)
                 */
                if (!ssl_init_wbio_buffer(s, 1)) {
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }

                ssl3_init_finished_mac(s);
                s->state = SSL3_ST_SR_CLNT_HELLO_A;
                s->ctx->stats.sess_accept++;
            } else if (!s->s3->send_connection_binding &&
                       !(s->options &
                         SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION)) {
                /*
                 * Server attempting to renegotiate with client that doesn't
                 * support secure renegotiation.
                 */
                SSLerr(SSL_F_SSL3_ACCEPT,
                       SSL_R_UNSAFE_LEGACY_RENEGOTIATION_DISABLED);
                ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
                ret = -1;
                s->state = SSL_ST_ERR;
                goto end;
            } else {
                /*
                 * s->state == SSL_ST_RENEGOTIATE, we will just send a
                 * HelloRequest
                 */
                s->ctx->stats.sess_accept_renegotiate++;
                s->state = SSL3_ST_SW_HELLO_REQ_A;
            }
            break;

        case SSL3_ST_SW_HELLO_REQ_A:
        case SSL3_ST_SW_HELLO_REQ_B:

            s->shutdown = 0;
            ret = ssl3_send_hello_request(s);
            if (ret <= 0)
                goto end;
            s->s3->tmp.next_state = SSL3_ST_SW_HELLO_REQ_C;
            s->state = SSL3_ST_SW_FLUSH;
            s->init_num = 0;

            ssl3_init_finished_mac(s);
            break;

        case SSL3_ST_SW_HELLO_REQ_C:
            s->state = SSL_ST_OK;
            break;

        case SSL3_ST_SR_CLNT_HELLO_A:
        case SSL3_ST_SR_CLNT_HELLO_B:
        case SSL3_ST_SR_CLNT_HELLO_C:

            s->shutdown = 0;
            ret = ssl3_get_client_hello(s);
            if (ret <= 0)
                goto end;
#ifndef OPENSSL_NO_SRP
            s->state = SSL3_ST_SR_CLNT_HELLO_D;
        case SSL3_ST_SR_CLNT_HELLO_D:
            {
                int al;
                if ((ret = ssl_check_srp_ext_ClientHello(s, &al)) < 0) {
                    /*
                     * callback indicates firther work to be done
                     */
                    s->rwstate = SSL_X509_LOOKUP;
                    goto end;
                }
                if (ret != SSL_ERROR_NONE) {
                    ssl3_send_alert(s, SSL3_AL_FATAL, al);
                    /*
                     * This is not really an error but the only means to for
                     * a client to detect whether srp is supported.
                     */
                    if (al != TLS1_AD_UNKNOWN_PSK_IDENTITY)
                        SSLerr(SSL_F_SSL3_ACCEPT, SSL_R_CLIENTHELLO_TLSEXT);
                    ret = SSL_TLSEXT_ERR_ALERT_FATAL;
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }
            }
#endif

            s->renegotiate = 2;
            s->state = SSL3_ST_SW_SRVR_HELLO_A;
            s->init_num = 0;
            break;

        case SSL3_ST_SW_SRVR_HELLO_A:
        case SSL3_ST_SW_SRVR_HELLO_B:
            ret = ssl3_send_server_hello(s);
            if (ret <= 0)
                goto end;
#ifndef OPENSSL_NO_TLSEXT
            if (s->hit) {
                if (s->tlsext_ticket_expected)
                    s->state = SSL3_ST_SW_SESSION_TICKET_A;
                else
                    s->state = SSL3_ST_SW_CHANGE_A;
            }
#else
            if (s->hit)
                s->state = SSL3_ST_SW_CHANGE_A;
#endif
            else
                s->state = SSL3_ST_SW_CERT_A;
            s->init_num = 0;
            break;

        case SSL3_ST_SW_CERT_A:
        case SSL3_ST_SW_CERT_B:
            /* Check if it is anon DH or anon ECDH, */
            /* normal PSK or KRB5 or SRP */
            if (!
                (s->s3->tmp.
                 new_cipher->algorithm_auth & (SSL_aNULL | SSL_aKRB5 |
                                               SSL_aSRP))
&& !(s->s3->tmp.new_cipher->algorithm_mkey & SSL_kPSK)) {
                ret = ssl3_send_server_certificate(s);
                if (ret <= 0)
                    goto end;
#ifndef OPENSSL_NO_TLSEXT
                if (s->tlsext_status_expected)
                    s->state = SSL3_ST_SW_CERT_STATUS_A;
                else
                    s->state = SSL3_ST_SW_KEY_EXCH_A;
            } else {
                skip = 1;
                s->state = SSL3_ST_SW_KEY_EXCH_A;
            }
#else
            } else
                skip = 1;

            s->state = SSL3_ST_SW_KEY_EXCH_A;
#endif
            s->init_num = 0;
            break;

        case SSL3_ST_SW_KEY_EXCH_A:
        case SSL3_ST_SW_KEY_EXCH_B:
            alg_k = s->s3->tmp.new_cipher->algorithm_mkey;

            /*
             * clear this, it may get reset by
             * send_server_key_exchange
             */
            s->s3->tmp.use_rsa_tmp = 0;

            /*
             * only send if a DH key exchange, fortezza or RSA but we have a
             * sign only certificate PSK: may send PSK identity hints For
             * ECC ciphersuites, we send a serverKeyExchange message only if
             * the cipher suite is either ECDH-anon or ECDHE. In other cases,
             * the server certificate contains the server's public key for
             * key exchange.
             */
            if (0
                /*
                 * PSK: send ServerKeyExchange if PSK identity hint if
                 * provided
                 */
#ifndef OPENSSL_NO_PSK
                || ((alg_k & SSL_kPSK) && s->ctx->psk_identity_hint)
#endif
#ifndef OPENSSL_NO_SRP
                /* SRP: send ServerKeyExchange */
                || (alg_k & SSL_kSRP)
#endif
                || (alg_k & SSL_kEDH)
                || (alg_k & SSL_kEECDH)
                || ((alg_k & SSL_kRSA)
                    && (s->cert->pkeys[SSL_PKEY_RSA_ENC].privatekey == NULL
                        || (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher)
                            && EVP_PKEY_size(s->cert->pkeys
                                             [SSL_PKEY_RSA_ENC].privatekey) *
                            8 > SSL_C_EXPORT_PKEYLENGTH(s->s3->tmp.new_cipher)
                        )
                    )
                )
                ) {
                ret = ssl3_send_server_key_exchange(s);
                if (ret <= 0)
                    goto end;
            } else
                skip = 1;

            s->state = SSL3_ST_SW_CERT_REQ_A;
            s->init_num = 0;
            break;

        case SSL3_ST_SW_CERT_REQ_A:
        case SSL3_ST_SW_CERT_REQ_B:
            if (                /* don't request cert unless asked for it: */
                   !(s->verify_mode & SSL_VERIFY_PEER) ||
                   /*
                    * if SSL_VERIFY_CLIENT_ONCE is set, don't request cert
                    * during re-negotiation:
                    */
                   ((s->session->peer != NULL) &&
                    (s->verify_mode & SSL_VERIFY_CLIENT_ONCE)) ||
                   /*
                    * never request cert in anonymous ciphersuites (see
                    * section "Certificate request" in SSL 3 drafts and in
                    * RFC 2246):
                    */
                   ((s->s3->tmp.new_cipher->algorithm_auth & SSL_aNULL) &&
                    /*
                     * ... except when the application insists on
                     * verification (against the specs, but s3_clnt.c accepts
                     * this for SSL 3)
                     */
                    !(s->verify_mode & SSL_VERIFY_FAIL_IF_NO_PEER_CERT)) ||
                   /*
                    * never request cert in Kerberos ciphersuites
                    */
                   (s->s3->tmp.new_cipher->algorithm_auth & SSL_aKRB5) ||
                   /* don't request certificate for SRP auth */
                   (s->s3->tmp.new_cipher->algorithm_auth & SSL_aSRP)
                   /*
                    * With normal PSK Certificates and Certificate Requests
                    * are omitted
                    */
                   || (s->s3->tmp.new_cipher->algorithm_mkey & SSL_kPSK)) {
                /* no cert request */
                skip = 1;
                s->s3->tmp.cert_request = 0;
                s->state = SSL3_ST_SW_SRVR_DONE_A;
                if (s->s3->handshake_buffer) {
                    if (!ssl3_digest_cached_records(s)) {
                        s->state = SSL_ST_ERR;
                        return -1;
                    }
                }
            } else {
                s->s3->tmp.cert_request = 1;
                ret = ssl3_send_certificate_request(s);
                if (ret <= 0)
                    goto end;
#ifndef NETSCAPE_HANG_BUG
                s->state = SSL3_ST_SW_SRVR_DONE_A;
#else
                s->state = SSL3_ST_SW_FLUSH;
                s->s3->tmp.next_state = SSL3_ST_SR_CERT_A;
#endif
                s->init_num = 0;
            }
            break;

        case SSL3_ST_SW_SRVR_DONE_A:
        case SSL3_ST_SW_SRVR_DONE_B:
            ret = ssl3_send_server_done(s);
            if (ret <= 0)
                goto end;
            s->s3->tmp.next_state = SSL3_ST_SR_CERT_A;
            s->state = SSL3_ST_SW_FLUSH;
            s->init_num = 0;
            break;

        case SSL3_ST_SW_FLUSH:

            /*
             * This code originally checked to see if any data was pending
             * using BIO_CTRL_INFO and then flushed. This caused problems as
             * documented in PR#1939. The proposed fix doesn't completely
             * resolve this issue as buggy implementations of
             * BIO_CTRL_PENDING still exist. So instead we just flush
             * unconditionally.
             */

            s->rwstate = SSL_WRITING;
            if (BIO_flush(s->wbio) <= 0) {
                ret = -1;
                goto end;
            }
            s->rwstate = SSL_NOTHING;

            s->state = s->s3->tmp.next_state;
            break;

        case SSL3_ST_SR_CERT_A:
        case SSL3_ST_SR_CERT_B:
            if (s->s3->tmp.cert_request) {
                ret = ssl3_get_client_certificate(s);
                if (ret <= 0)
                    goto end;
            }
            s->init_num = 0;
            s->state = SSL3_ST_SR_KEY_EXCH_A;
            break;

        case SSL3_ST_SR_KEY_EXCH_A:
        case SSL3_ST_SR_KEY_EXCH_B:
            ret = ssl3_get_client_key_exchange(s);
            if (ret <= 0)
                goto end;
            if (ret == 2) {
                /*
                 * For the ECDH ciphersuites when the client sends its ECDH
                 * pub key in a certificate, the CertificateVerify message is
                 * not sent. Also for GOST ciphersuites when the client uses
                 * its key from the certificate for key exchange.
                 */
#if defined(OPENSSL_NO_TLSEXT) || defined(OPENSSL_NO_NEXTPROTONEG)
                s->state = SSL3_ST_SR_FINISHED_A;
#else
                if (s->s3->next_proto_neg_seen)
                    s->state = SSL3_ST_SR_NEXT_PROTO_A;
                else
                    s->state = SSL3_ST_SR_FINISHED_A;
#endif
                s->init_num = 0;
            } else if (SSL_USE_SIGALGS(s)) {
                s->state = SSL3_ST_SR_CERT_VRFY_A;
                s->init_num = 0;
                if (!s->session->peer)
                    break;
                /*
                 * For sigalgs freeze the handshake buffer at this point and
                 * digest cached records.
                 */
                if (!s->s3->handshake_buffer) {
                    SSLerr(SSL_F_SSL3_ACCEPT, ERR_R_INTERNAL_ERROR);
                    s->state = SSL_ST_ERR;
                    return -1;
                }
                s->s3->flags |= TLS1_FLAGS_KEEP_HANDSHAKE;
                if (!ssl3_digest_cached_records(s)) {
                    s->state = SSL_ST_ERR;
                    return -1;
                }
            } else {
                int offset = 0;
                int dgst_num;

                s->state = SSL3_ST_SR_CERT_VRFY_A;
                s->init_num = 0;

                /*
                 * We need to get hashes here so if there is a client cert,
                 * it can be verified FIXME - digest processing for
                 * CertificateVerify should be generalized. But it is next
                 * step
                 */
                if (s->s3->handshake_buffer) {
                    if (!ssl3_digest_cached_records(s)) {
                        s->state = SSL_ST_ERR;
                        return -1;
                    }
                }
                for (dgst_num = 0; dgst_num < SSL_MAX_DIGEST; dgst_num++)
                    if (s->s3->handshake_dgst[dgst_num]) {
                        int dgst_size;

                        s->method->ssl3_enc->cert_verify_mac(s,
                                                             EVP_MD_CTX_type
                                                             (s->
                                                              s3->handshake_dgst
                                                              [dgst_num]),
                                                             &(s->s3->
                                                               tmp.cert_verify_md
                                                               [offset]));
                        dgst_size =
                            EVP_MD_CTX_size(s->s3->handshake_dgst[dgst_num]);
                        if (dgst_size < 0) {
                            s->state = SSL_ST_ERR;
                            ret = -1;
                            goto end;
                        }
                        offset += dgst_size;
                    }
            }
            break;

        case SSL3_ST_SR_CERT_VRFY_A:
        case SSL3_ST_SR_CERT_VRFY_B:
            ret = ssl3_get_cert_verify(s);
            if (ret <= 0)
                goto end;

#if defined(OPENSSL_NO_TLSEXT) || defined(OPENSSL_NO_NEXTPROTONEG)
            s->state = SSL3_ST_SR_FINISHED_A;
#else
            if (s->s3->next_proto_neg_seen)
                s->state = SSL3_ST_SR_NEXT_PROTO_A;
            else
                s->state = SSL3_ST_SR_FINISHED_A;
#endif
            s->init_num = 0;
            break;

#if !defined(OPENSSL_NO_TLSEXT) && !defined(OPENSSL_NO_NEXTPROTONEG)
        case SSL3_ST_SR_NEXT_PROTO_A:
        case SSL3_ST_SR_NEXT_PROTO_B:
            /*
             * Enable CCS for NPN. Receiving a CCS clears the flag, so make
             * sure not to re-enable it to ban duplicates. This *should* be the
             * first time we have received one - but we check anyway to be
             * cautious.
             * s->s3->change_cipher_spec is set when a CCS is
             * processed in s3_pkt.c, and remains set until
             * the client's Finished message is read.
             */
            if (!s->s3->change_cipher_spec)
                s->s3->flags |= SSL3_FLAGS_CCS_OK;

            ret = ssl3_get_next_proto(s);
            if (ret <= 0)
                goto end;
            s->init_num = 0;
            s->state = SSL3_ST_SR_FINISHED_A;
            break;
#endif

        case SSL3_ST_SR_FINISHED_A:
        case SSL3_ST_SR_FINISHED_B:
            /*
             * Enable CCS for handshakes without NPN. In NPN the CCS flag has
             * already been set. Receiving a CCS clears the flag, so make
             * sure not to re-enable it to ban duplicates.
             * s->s3->change_cipher_spec is set when a CCS is
             * processed in s3_pkt.c, and remains set until
             * the client's Finished message is read.
             */
            if (!s->s3->change_cipher_spec)
                s->s3->flags |= SSL3_FLAGS_CCS_OK;
            ret = ssl3_get_finished(s, SSL3_ST_SR_FINISHED_A,
                                    SSL3_ST_SR_FINISHED_B);
            if (ret <= 0)
                goto end;
            if (s->hit)
                s->state = SSL_ST_OK;
#ifndef OPENSSL_NO_TLSEXT
            else if (s->tlsext_ticket_expected)
                s->state = SSL3_ST_SW_SESSION_TICKET_A;
#endif
            else
                s->state = SSL3_ST_SW_CHANGE_A;
            s->init_num = 0;
            break;

#ifndef OPENSSL_NO_TLSEXT
        case SSL3_ST_SW_SESSION_TICKET_A:
        case SSL3_ST_SW_SESSION_TICKET_B:
            ret = ssl3_send_newsession_ticket(s);
            if (ret <= 0)
                goto end;
            s->state = SSL3_ST_SW_CHANGE_A;
            s->init_num = 0;
            break;

        case SSL3_ST_SW_CERT_STATUS_A:
        case SSL3_ST_SW_CERT_STATUS_B:
            ret = ssl3_send_cert_status(s);
            if (ret <= 0)
                goto end;
            s->state = SSL3_ST_SW_KEY_EXCH_A;
            s->init_num = 0;
            break;

#endif

        case SSL3_ST_SW_CHANGE_A:
        case SSL3_ST_SW_CHANGE_B:

            s->session->cipher = s->s3->tmp.new_cipher;
            if (!s->method->ssl3_enc->setup_key_block(s)) {
                ret = -1;
                s->state = SSL_ST_ERR;
                goto end;
            }

            ret = ssl3_send_change_cipher_spec(s,
                                               SSL3_ST_SW_CHANGE_A,
                                               SSL3_ST_SW_CHANGE_B);

            if (ret <= 0)
                goto end;
            s->state = SSL3_ST_SW_FINISHED_A;
            s->init_num = 0;

            if (!s->method->ssl3_enc->change_cipher_state(s,
                                                          SSL3_CHANGE_CIPHER_SERVER_WRITE))
            {
                ret = -1;
                s->state = SSL_ST_ERR;
                goto end;
            }

            break;

        case SSL3_ST_SW_FINISHED_A:
        case SSL3_ST_SW_FINISHED_B:
            ret = ssl3_send_finished(s,
                                     SSL3_ST_SW_FINISHED_A,
                                     SSL3_ST_SW_FINISHED_B,
                                     s->method->
                                     ssl3_enc->server_finished_label,
                                     s->method->
                                     ssl3_enc->server_finished_label_len);
            if (ret <= 0)
                goto end;
            s->state = SSL3_ST_SW_FLUSH;
            if (s->hit) {
#if defined(OPENSSL_NO_TLSEXT) || defined(OPENSSL_NO_NEXTPROTONEG)
                s->s3->tmp.next_state = SSL3_ST_SR_FINISHED_A;
#else
                if (s->s3->next_proto_neg_seen) {
                    s->s3->tmp.next_state = SSL3_ST_SR_NEXT_PROTO_A;
                } else
                    s->s3->tmp.next_state = SSL3_ST_SR_FINISHED_A;
#endif
            } else
                s->s3->tmp.next_state = SSL_ST_OK;
            s->init_num = 0;
            break;

        case SSL_ST_OK:
            /* clean a few things up */
            ssl3_cleanup_key_block(s);

            BUF_MEM_free(s->init_buf);
            s->init_buf = NULL;

            /* remove buffering on output */
            ssl_free_wbio_buffer(s);

            s->init_num = 0;

            if (s->renegotiate == 2) { /* skipped if we just sent a
                                        * HelloRequest */
                s->renegotiate = 0;
                s->new_session = 0;

                ssl_update_cache(s, SSL_SESS_CACHE_SERVER);

                s->ctx->stats.sess_accept_good++;
                /* s->server=1; */
                s->handshake_func = ssl3_accept;

                if (cb != NULL)
                    cb(s, SSL_CB_HANDSHAKE_DONE, 1);
            }

            ret = 1;
            goto end;
            /* break; */

        case SSL_ST_ERR:
        default:
            SSLerr(SSL_F_SSL3_ACCEPT, SSL_R_UNKNOWN_STATE);
            ret = -1;
            goto end;
            /* break; */
        }

        if (!s->s3->tmp.reuse_message && !skip) {
            if (s->debug) {
                if ((ret = BIO_flush(s->wbio)) <= 0)
                    goto end;
            }

            if ((cb != NULL) && (s->state != state)) {
                new_state = s->state;
                s->state = state;
                cb(s, SSL_CB_ACCEPT_LOOP, 1);
                s->state = new_state;
            }
        }
        skip = 0;
    }

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.