Optimize session cache flushing

[thirdparty/openssl.git] / ssl / ssl_sess.c

/*
 * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
 * Copyright 2005 Nokia. All rights reserved.
 *
 * Licensed under the Apache License 2.0 (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
 */

#if defined(__TANDEM) && defined(_SPT_MODEL_)
# include <spthread.h>
# include <spt_extensions.h> /* timeval */
#endif
#include <stdio.h>
#include <openssl/rand.h>
#include <openssl/engine.h>
#include "internal/refcount.h"
#include "internal/cryptlib.h"
#include "ssl_local.h"
#include "statem/statem_local.h"

static void SSL_SESSION_list_remove(SSL_CTX *ctx, SSL_SESSION *s);
static void SSL_SESSION_list_add(SSL_CTX *ctx, SSL_SESSION *s);
static int remove_session_lock(SSL_CTX *ctx, SSL_SESSION *c, int lck);

DEFINE_STACK_OF(SSL_SESSION)

__owur static int sess_timedout(time_t t, SSL_SESSION *ss)
{
    /* if timeout overflowed, it can never timeout! */
    if (ss->timeout_ovf)
        return 0;
    return t > ss->calc_timeout;
}

/*
 * Returns -1/0/+1 as other XXXcmp-type functions
 * Takes overflow of calculated timeout into consideration
 */
__owur static int timeoutcmp(SSL_SESSION *a, SSL_SESSION *b)
{
    /* if only one overflowed, then it is greater */
    if (a->timeout_ovf && !b->timeout_ovf)
        return 1;
    if (!a->timeout_ovf && b->timeout_ovf)
        return -1;
    /* No overflow, or both overflowed, so straight compare is safe */
    if (a->calc_timeout < b->calc_timeout)
        return -1;
    if (a->calc_timeout > b->calc_timeout)
        return 1;
    return 0;
}

/*
 * Calculates effective timeout, saving overflow state
 * Locking must be done by the caller of this function
 */
void ssl_session_calculate_timeout(SSL_SESSION *ss)
{
    /* Force positive timeout */
    if (ss->timeout < 0)
        ss->timeout = 0;
    ss->calc_timeout = ss->time + ss->timeout;
    /*
     * |timeout| is always zero or positive, so the check for
     * overflow only needs to consider if |time| is positive
     */
    ss->timeout_ovf = ss->time > 0 && ss->calc_timeout < ss->time;
    /*
     * N.B. Realistic overflow can only occur in our lifetimes on a
     *      32-bit machine in January 2038.
     *      However, There are no controls to limit the |timeout|
     *      value, except to keep it positive.
     */
}

/*
 * SSL_get_session() and SSL_get1_session() are problematic in TLS1.3 because,
 * unlike in earlier protocol versions, the session ticket may not have been
 * sent yet even though a handshake has finished. The session ticket data could
 * come in sometime later...or even change if multiple session ticket messages
 * are sent from the server. The preferred way for applications to obtain
 * a resumable session is to use SSL_CTX_sess_set_new_cb().
 */

SSL_SESSION *SSL_get_session(const SSL *ssl)
/* aka SSL_get0_session; gets 0 objects, just returns a copy of the pointer */
{
    return ssl->session;
}

SSL_SESSION *SSL_get1_session(SSL *ssl)
/* variant of SSL_get_session: caller really gets something */
{
    SSL_SESSION *sess;
    /*
     * Need to lock this all up rather than just use CRYPTO_add so that
     * somebody doesn't free ssl->session between when we check it's non-null
     * and when we up the reference count.
     */
    if (!CRYPTO_THREAD_read_lock(ssl->lock))
        return NULL;
    sess = ssl->session;
    if (sess)
        SSL_SESSION_up_ref(sess);
    CRYPTO_THREAD_unlock(ssl->lock);
    return sess;
}

int SSL_SESSION_set_ex_data(SSL_SESSION *s, int idx, void *arg)
{
    return CRYPTO_set_ex_data(&s->ex_data, idx, arg);
}

void *SSL_SESSION_get_ex_data(const SSL_SESSION *s, int idx)
{
    return CRYPTO_get_ex_data(&s->ex_data, idx);
}

SSL_SESSION *SSL_SESSION_new(void)
{
    SSL_SESSION *ss;

    if (!OPENSSL_init_ssl(OPENSSL_INIT_LOAD_SSL_STRINGS, NULL))
        return NULL;

    ss = OPENSSL_zalloc(sizeof(*ss));
    if (ss == NULL) {
        ERR_raise(ERR_LIB_SSL, ERR_R_MALLOC_FAILURE);
        return NULL;
    }

    ss->verify_result = 1;      /* avoid 0 (= X509_V_OK) just in case */
    ss->references = 1;
    ss->timeout = 60 * 5 + 4;   /* 5 minute timeout by default */
    ss->time = time(NULL);
    ssl_session_calculate_timeout(ss);
    ss->lock = CRYPTO_THREAD_lock_new();
    if (ss->lock == NULL) {
        ERR_raise(ERR_LIB_SSL, ERR_R_MALLOC_FAILURE);
        OPENSSL_free(ss);
        return NULL;
    }

    if (!CRYPTO_new_ex_data(CRYPTO_EX_INDEX_SSL_SESSION, ss, &ss->ex_data)) {
        CRYPTO_THREAD_lock_free(ss->lock);
        OPENSSL_free(ss);
        return NULL;
    }
    return ss;
}

SSL_SESSION *SSL_SESSION_dup(const SSL_SESSION *src)
{
    return ssl_session_dup(src, 1);
}

/*
 * Create a new SSL_SESSION and duplicate the contents of |src| into it. If
 * ticket == 0 then no ticket information is duplicated, otherwise it is.
 */
SSL_SESSION *ssl_session_dup(const SSL_SESSION *src, int ticket)
{
    SSL_SESSION *dest;

    dest = OPENSSL_malloc(sizeof(*dest));
    if (dest == NULL) {
        goto err;
    }
    memcpy(dest, src, sizeof(*dest));

    /*
     * Set the various pointers to NULL so that we can call SSL_SESSION_free in
     * the case of an error whilst halfway through constructing dest
     */
#ifndef OPENSSL_NO_PSK
    dest->psk_identity_hint = NULL;
    dest->psk_identity = NULL;
#endif
    dest->ext.hostname = NULL;
    dest->ext.tick = NULL;
    dest->ext.alpn_selected = NULL;
#ifndef OPENSSL_NO_SRP
    dest->srp_username = NULL;
#endif
    dest->peer_chain = NULL;
    dest->peer = NULL;
    dest->ticket_appdata = NULL;
    memset(&dest->ex_data, 0, sizeof(dest->ex_data));

    /* We deliberately don't copy the prev and next pointers */
    dest->prev = NULL;
    dest->next = NULL;

    dest->references = 1;

    dest->lock = CRYPTO_THREAD_lock_new();
    if (dest->lock == NULL)
        goto err;

    if (!CRYPTO_new_ex_data(CRYPTO_EX_INDEX_SSL_SESSION, dest, &dest->ex_data))
        goto err;

    if (src->peer != NULL) {
        if (!X509_up_ref(src->peer))
            goto err;
        dest->peer = src->peer;
    }

    if (src->peer_chain != NULL) {
        dest->peer_chain = X509_chain_up_ref(src->peer_chain);
        if (dest->peer_chain == NULL)
            goto err;
    }
#ifndef OPENSSL_NO_PSK
    if (src->psk_identity_hint) {
        dest->psk_identity_hint = OPENSSL_strdup(src->psk_identity_hint);
        if (dest->psk_identity_hint == NULL) {
            goto err;
        }
    }
    if (src->psk_identity) {
        dest->psk_identity = OPENSSL_strdup(src->psk_identity);
        if (dest->psk_identity == NULL) {
            goto err;
        }
    }
#endif

    if (!CRYPTO_dup_ex_data(CRYPTO_EX_INDEX_SSL_SESSION,
                            &dest->ex_data, &src->ex_data)) {
        goto err;
    }

    if (src->ext.hostname) {
        dest->ext.hostname = OPENSSL_strdup(src->ext.hostname);
        if (dest->ext.hostname == NULL) {
            goto err;
        }
    }

    if (ticket != 0 && src->ext.tick != NULL) {
        dest->ext.tick =
            OPENSSL_memdup(src->ext.tick, src->ext.ticklen);
        if (dest->ext.tick == NULL)
            goto err;
    } else {
        dest->ext.tick_lifetime_hint = 0;
        dest->ext.ticklen = 0;
    }

    if (src->ext.alpn_selected != NULL) {
        dest->ext.alpn_selected = OPENSSL_memdup(src->ext.alpn_selected,
                                                 src->ext.alpn_selected_len);
        if (dest->ext.alpn_selected == NULL)
            goto err;
    }

#ifndef OPENSSL_NO_SRP
    if (src->srp_username) {
        dest->srp_username = OPENSSL_strdup(src->srp_username);
        if (dest->srp_username == NULL) {
            goto err;
        }
    }
#endif

    if (src->ticket_appdata != NULL) {
        dest->ticket_appdata =
            OPENSSL_memdup(src->ticket_appdata, src->ticket_appdata_len);
        if (dest->ticket_appdata == NULL)
            goto err;
    }

    return dest;
 err:
    ERR_raise(ERR_LIB_SSL, ERR_R_MALLOC_FAILURE);
    SSL_SESSION_free(dest);
    return NULL;
}

const unsigned char *SSL_SESSION_get_id(const SSL_SESSION *s, unsigned int *len)
{
    if (len)
        *len = (unsigned int)s->session_id_length;
    return s->session_id;
}
const unsigned char *SSL_SESSION_get0_id_context(const SSL_SESSION *s,
                                                unsigned int *len)
{
    if (len != NULL)
        *len = (unsigned int)s->sid_ctx_length;
    return s->sid_ctx;
}

unsigned int SSL_SESSION_get_compress_id(const SSL_SESSION *s)
{
    return s->compress_meth;
}

/*
 * SSLv3/TLSv1 has 32 bytes (256 bits) of session ID space. As such, filling
 * the ID with random junk repeatedly until we have no conflict is going to
 * complete in one iteration pretty much "most" of the time (btw:
 * understatement). So, if it takes us 10 iterations and we still can't avoid
 * a conflict - well that's a reasonable point to call it quits. Either the
 * RAND code is broken or someone is trying to open roughly very close to
 * 2^256 SSL sessions to our server. How you might store that many sessions
 * is perhaps a more interesting question ...
 */

#define MAX_SESS_ID_ATTEMPTS 10
static int def_generate_session_id(SSL *ssl, unsigned char *id,
                                   unsigned int *id_len)
{
    unsigned int retry = 0;
    do
        if (RAND_bytes_ex(ssl->ctx->libctx, id, *id_len, 0) <= 0)
            return 0;
    while (SSL_has_matching_session_id(ssl, id, *id_len) &&
           (++retry < MAX_SESS_ID_ATTEMPTS)) ;
    if (retry < MAX_SESS_ID_ATTEMPTS)
        return 1;
    /* else - woops a session_id match */
    /*
     * XXX We should also check the external cache -- but the probability of
     * a collision is negligible, and we could not prevent the concurrent
     * creation of sessions with identical IDs since we currently don't have
     * means to atomically check whether a session ID already exists and make
     * a reservation for it if it does not (this problem applies to the
     * internal cache as well).
     */
    return 0;
}

int ssl_generate_session_id(SSL *s, SSL_SESSION *ss)
{
    unsigned int tmp;
    GEN_SESSION_CB cb = def_generate_session_id;

    switch (s->version) {
    case SSL3_VERSION:
    case TLS1_VERSION:
    case TLS1_1_VERSION:
    case TLS1_2_VERSION:
    case TLS1_3_VERSION:
    case DTLS1_BAD_VER:
    case DTLS1_VERSION:
    case DTLS1_2_VERSION:
        ss->session_id_length = SSL3_SSL_SESSION_ID_LENGTH;
        break;
    default:
        SSLfatal(s, SSL_AD_INTERNAL_ERROR, SSL_R_UNSUPPORTED_SSL_VERSION);
        return 0;
    }

    /*-
     * If RFC5077 ticket, use empty session ID (as server).
     * Note that:
     * (a) ssl_get_prev_session() does lookahead into the
     *     ClientHello extensions to find the session ticket.
     *     When ssl_get_prev_session() fails, statem_srvr.c calls
     *     ssl_get_new_session() in tls_process_client_hello().
     *     At that point, it has not yet parsed the extensions,
     *     however, because of the lookahead, it already knows
     *     whether a ticket is expected or not.
     *
     * (b) statem_clnt.c calls ssl_get_new_session() before parsing
     *     ServerHello extensions, and before recording the session
     *     ID received from the server, so this block is a noop.
     */
    if (s->ext.ticket_expected) {
        ss->session_id_length = 0;
        return 1;
    }

    /* Choose which callback will set the session ID */
    if (!CRYPTO_THREAD_read_lock(s->lock))
        return 0;
    if (!CRYPTO_THREAD_read_lock(s->session_ctx->lock)) {
        CRYPTO_THREAD_unlock(s->lock);
        SSLfatal(s, SSL_AD_INTERNAL_ERROR,
                 SSL_R_SESSION_ID_CONTEXT_UNINITIALIZED);
        return 0;
    }
    if (s->generate_session_id)
        cb = s->generate_session_id;
    else if (s->session_ctx->generate_session_id)
        cb = s->session_ctx->generate_session_id;
    CRYPTO_THREAD_unlock(s->session_ctx->lock);
    CRYPTO_THREAD_unlock(s->lock);
    /* Choose a session ID */
    memset(ss->session_id, 0, ss->session_id_length);
    tmp = (int)ss->session_id_length;
    if (!cb(s, ss->session_id, &tmp)) {
        /* The callback failed */
        SSLfatal(s, SSL_AD_INTERNAL_ERROR,
                 SSL_R_SSL_SESSION_ID_CALLBACK_FAILED);
        return 0;
    }
    /*
     * Don't allow the callback to set the session length to zero. nor
     * set it higher than it was.
     */
    if (tmp == 0 || tmp > ss->session_id_length) {
        /* The callback set an illegal length */
        SSLfatal(s, SSL_AD_INTERNAL_ERROR,
                 SSL_R_SSL_SESSION_ID_HAS_BAD_LENGTH);
        return 0;
    }
    ss->session_id_length = tmp;
    /* Finally, check for a conflict */
    if (SSL_has_matching_session_id(s, ss->session_id,
                                    (unsigned int)ss->session_id_length)) {
        SSLfatal(s, SSL_AD_INTERNAL_ERROR, SSL_R_SSL_SESSION_ID_CONFLICT);
        return 0;
    }

    return 1;
}

int ssl_get_new_session(SSL *s, int session)
{
    /* This gets used by clients and servers. */

    SSL_SESSION *ss = NULL;

    if ((ss = SSL_SESSION_new()) == NULL) {
        SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_MALLOC_FAILURE);
        return 0;
    }

    /* If the context has a default timeout, use it */
    if (s->session_ctx->session_timeout == 0)
        ss->timeout = SSL_get_default_timeout(s);
    else
        ss->timeout = s->session_ctx->session_timeout;

    SSL_SESSION_free(s->session);
    s->session = NULL;

    if (session) {
        if (SSL_IS_TLS13(s)) {
            /*
             * We generate the session id while constructing the
             * NewSessionTicket in TLSv1.3.
             */
            ss->session_id_length = 0;
        } else if (!ssl_generate_session_id(s, ss)) {
            /* SSLfatal() already called */
            SSL_SESSION_free(ss);
            return 0;
        }

    } else {
        ss->session_id_length = 0;
    }

    if (s->sid_ctx_length > sizeof(ss->sid_ctx)) {
        SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR);
        SSL_SESSION_free(ss);
        return 0;
    }
    memcpy(ss->sid_ctx, s->sid_ctx, s->sid_ctx_length);
    ss->sid_ctx_length = s->sid_ctx_length;
    s->session = ss;
    ss->ssl_version = s->version;
    ss->verify_result = X509_V_OK;

    /* If client supports extended master secret set it in session */
    if (s->s3.flags & TLS1_FLAGS_RECEIVED_EXTMS)
        ss->flags |= SSL_SESS_FLAG_EXTMS;

    return 1;
}

SSL_SESSION *lookup_sess_in_cache(SSL *s, const unsigned char *sess_id,
                                  size_t sess_id_len)
{
    SSL_SESSION *ret = NULL;

    if ((s->session_ctx->session_cache_mode
         & SSL_SESS_CACHE_NO_INTERNAL_LOOKUP) == 0) {
        SSL_SESSION data;

        data.ssl_version = s->version;
        if (!ossl_assert(sess_id_len <= SSL_MAX_SSL_SESSION_ID_LENGTH))
            return NULL;

        memcpy(data.session_id, sess_id, sess_id_len);
        data.session_id_length = sess_id_len;

        if (!CRYPTO_THREAD_read_lock(s->session_ctx->lock))
            return NULL;
        ret = lh_SSL_SESSION_retrieve(s->session_ctx->sessions, &data);
        if (ret != NULL) {
            /* don't allow other threads to steal it: */
            SSL_SESSION_up_ref(ret);
        }
        CRYPTO_THREAD_unlock(s->session_ctx->lock);
        if (ret == NULL)
            tsan_counter(&s->session_ctx->stats.sess_miss);
    }

    if (ret == NULL && s->session_ctx->get_session_cb != NULL) {
        int copy = 1;

        ret = s->session_ctx->get_session_cb(s, sess_id, sess_id_len, &copy);

        if (ret != NULL) {
            tsan_counter(&s->session_ctx->stats.sess_cb_hit);

            /*
             * Increment reference count now if the session callback asks us
             * to do so (note that if the session structures returned by the
             * callback are shared between threads, it must handle the
             * reference count itself [i.e. copy == 0], or things won't be
             * thread-safe).
             */
            if (copy)
                SSL_SESSION_up_ref(ret);

            /*
             * Add the externally cached session to the internal cache as
             * well if and only if we are supposed to.
             */
            if ((s->session_ctx->session_cache_mode &
                 SSL_SESS_CACHE_NO_INTERNAL_STORE) == 0) {
                /*
                 * Either return value of SSL_CTX_add_session should not
                 * interrupt the session resumption process. The return
                 * value is intentionally ignored.
                 */
                (void)SSL_CTX_add_session(s->session_ctx, ret);
            }
        }
    }

    return ret;
}

/*-
 * ssl_get_prev attempts to find an SSL_SESSION to be used to resume this
 * connection. It is only called by servers.
 *
 *   hello: The parsed ClientHello data
 *
 * Returns:
 *   -1: fatal error
 *    0: no session found
 *    1: a session may have been found.
 *
 * Side effects:
 *   - If a session is found then s->session is pointed at it (after freeing an
 *     existing session if need be) and s->verify_result is set from the session.
 *   - Both for new and resumed sessions, s->ext.ticket_expected is set to 1
 *     if the server should issue a new session ticket (to 0 otherwise).
 */
int ssl_get_prev_session(SSL *s, CLIENTHELLO_MSG *hello)
{
    /* This is used only by servers. */

    SSL_SESSION *ret = NULL;
    int fatal = 0;
    int try_session_cache = 0;
    SSL_TICKET_STATUS r;

    if (SSL_IS_TLS13(s)) {
        /*
         * By default we will send a new ticket. This can be overridden in the
         * ticket processing.
         */
        s->ext.ticket_expected = 1;
        if (!tls_parse_extension(s, TLSEXT_IDX_psk_kex_modes,
                                 SSL_EXT_CLIENT_HELLO, hello->pre_proc_exts,
                                 NULL, 0)
                || !tls_parse_extension(s, TLSEXT_IDX_psk, SSL_EXT_CLIENT_HELLO,
                                        hello->pre_proc_exts, NULL, 0))
            return -1;

        ret = s->session;
    } else {
        /* sets s->ext.ticket_expected */
        r = tls_get_ticket_from_client(s, hello, &ret);
        switch (r) {
        case SSL_TICKET_FATAL_ERR_MALLOC:
        case SSL_TICKET_FATAL_ERR_OTHER:
            fatal = 1;
            SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR);
            goto err;
        case SSL_TICKET_NONE:
        case SSL_TICKET_EMPTY:
            if (hello->session_id_len > 0) {
                try_session_cache = 1;
                ret = lookup_sess_in_cache(s, hello->session_id,
                                           hello->session_id_len);
            }
            break;
        case SSL_TICKET_NO_DECRYPT:
        case SSL_TICKET_SUCCESS:
        case SSL_TICKET_SUCCESS_RENEW:
            break;
        }
    }

    if (ret == NULL)
        goto err;

    /* Now ret is non-NULL and we own one of its reference counts. */

    /* Check TLS version consistency */
    if (ret->ssl_version != s->version)
        goto err;

    if (ret->sid_ctx_length != s->sid_ctx_length
        || memcmp(ret->sid_ctx, s->sid_ctx, ret->sid_ctx_length)) {
        /*
         * We have the session requested by the client, but we don't want to
         * use it in this context.
         */
        goto err;               /* treat like cache miss */
    }

    if ((s->verify_mode & SSL_VERIFY_PEER) && s->sid_ctx_length == 0) {
        /*
         * We can't be sure if this session is being used out of context,
         * which is especially important for SSL_VERIFY_PEER. The application
         * should have used SSL[_CTX]_set_session_id_context. For this error
         * case, we generate an error instead of treating the event like a
         * cache miss (otherwise it would be easy for applications to
         * effectively disable the session cache by accident without anyone
         * noticing).
         */

        SSLfatal(s, SSL_AD_INTERNAL_ERROR,
                 SSL_R_SESSION_ID_CONTEXT_UNINITIALIZED);
        fatal = 1;
        goto err;
    }

    if (sess_timedout(time(NULL), ret)) {
        tsan_counter(&s->session_ctx->stats.sess_timeout);
        if (try_session_cache) {
            /* session was from the cache, so remove it */
            SSL_CTX_remove_session(s->session_ctx, ret);
        }
        goto err;
    }

    /* Check extended master secret extension consistency */
    if (ret->flags & SSL_SESS_FLAG_EXTMS) {
        /* If old session includes extms, but new does not: abort handshake */
        if (!(s->s3.flags & TLS1_FLAGS_RECEIVED_EXTMS)) {
            SSLfatal(s, SSL_AD_ILLEGAL_PARAMETER, SSL_R_INCONSISTENT_EXTMS);
            fatal = 1;
            goto err;
        }
    } else if (s->s3.flags & TLS1_FLAGS_RECEIVED_EXTMS) {
        /* If new session includes extms, but old does not: do not resume */
        goto err;
    }

    if (!SSL_IS_TLS13(s)) {
        /* We already did this for TLS1.3 */
        SSL_SESSION_free(s->session);
        s->session = ret;
    }

    tsan_counter(&s->session_ctx->stats.sess_hit);
    s->verify_result = s->session->verify_result;
    return 1;

 err:
    if (ret != NULL) {
        SSL_SESSION_free(ret);
        /* In TLSv1.3 s->session was already set to ret, so we NULL it out */
        if (SSL_IS_TLS13(s))
            s->session = NULL;

        if (!try_session_cache) {
            /*
             * The session was from a ticket, so we should issue a ticket for
             * the new session
             */
            s->ext.ticket_expected = 1;
        }
    }
    if (fatal)
        return -1;

    return 0;
}

int SSL_CTX_add_session(SSL_CTX *ctx, SSL_SESSION *c)
{
    int ret = 0;
    SSL_SESSION *s;

    /*
     * add just 1 reference count for the SSL_CTX's session cache even though
     * it has two ways of access: each session is in a doubly linked list and
     * an lhash
     */
    SSL_SESSION_up_ref(c);
    /*
     * if session c is in already in cache, we take back the increment later
     */

    if (!CRYPTO_THREAD_write_lock(ctx->lock)) {
        SSL_SESSION_free(c);
        return 0;
    }
    s = lh_SSL_SESSION_insert(ctx->sessions, c);

    /*
     * s != NULL iff we already had a session with the given PID. In this
     * case, s == c should hold (then we did not really modify
     * ctx->sessions), or we're in trouble.
     */
    if (s != NULL && s != c) {
        /* We *are* in trouble ... */
        SSL_SESSION_list_remove(ctx, s);
        SSL_SESSION_free(s);
        /*
         * ... so pretend the other session did not exist in cache (we cannot
         * handle two SSL_SESSION structures with identical session ID in the
         * same cache, which could happen e.g. when two threads concurrently
         * obtain the same session from an external cache)
         */
        s = NULL;
    } else if (s == NULL &&
               lh_SSL_SESSION_retrieve(ctx->sessions, c) == NULL) {
        /* s == NULL can also mean OOM error in lh_SSL_SESSION_insert ... */

        /*
         * ... so take back the extra reference and also don't add
         * the session to the SSL_SESSION_list at this time
         */
        s = c;
    }

    /* Adjust last used time, and add back into the cache at the appropriate spot */
    if (ctx->session_cache_mode & SSL_SESS_CACHE_UPDATE_TIME) {
        c->time = time(NULL);
        ssl_session_calculate_timeout(c);
    }
    SSL_SESSION_list_add(ctx, c);

    if (s != NULL) {
        /*
         * existing cache entry -- decrement previously incremented reference
         * count because it already takes into account the cache
         */

        SSL_SESSION_free(s);    /* s == c */
        ret = 0;
    } else {
        /*
         * new cache entry -- remove old ones if cache has become too large
         */

        ret = 1;

        if (SSL_CTX_sess_get_cache_size(ctx) > 0) {
            while (SSL_CTX_sess_number(ctx) > SSL_CTX_sess_get_cache_size(ctx)) {
                if (!remove_session_lock(ctx, ctx->session_cache_tail, 0))
                    break;
                else
                    tsan_counter(&ctx->stats.sess_cache_full);
            }
        }
    }
    CRYPTO_THREAD_unlock(ctx->lock);
    return ret;
}

int SSL_CTX_remove_session(SSL_CTX *ctx, SSL_SESSION *c)
{
    return remove_session_lock(ctx, c, 1);
}

static int remove_session_lock(SSL_CTX *ctx, SSL_SESSION *c, int lck)
{
    SSL_SESSION *r;
    int ret = 0;

    if ((c != NULL) && (c->session_id_length != 0)) {
        if (lck) {
            if (!CRYPTO_THREAD_write_lock(ctx->lock))
                return 0;
        }
        if ((r = lh_SSL_SESSION_retrieve(ctx->sessions, c)) != NULL) {
            ret = 1;
            r = lh_SSL_SESSION_delete(ctx->sessions, r);
            SSL_SESSION_list_remove(ctx, r);
        }
        c->not_resumable = 1;

        if (lck)
            CRYPTO_THREAD_unlock(ctx->lock);

        if (ctx->remove_session_cb != NULL)
            ctx->remove_session_cb(ctx, c);

        if (ret)
            SSL_SESSION_free(r);
    }
    return ret;
}

void SSL_SESSION_free(SSL_SESSION *ss)
{
    int i;

    if (ss == NULL)
        return;
    CRYPTO_DOWN_REF(&ss->references, &i, ss->lock);
    REF_PRINT_COUNT("SSL_SESSION", ss);
    if (i > 0)
        return;
    REF_ASSERT_ISNT(i < 0);

    CRYPTO_free_ex_data(CRYPTO_EX_INDEX_SSL_SESSION, ss, &ss->ex_data);

    OPENSSL_cleanse(ss->master_key, sizeof(ss->master_key));
    OPENSSL_cleanse(ss->session_id, sizeof(ss->session_id));
    X509_free(ss->peer);
    sk_X509_pop_free(ss->peer_chain, X509_free);
    OPENSSL_free(ss->ext.hostname);
    OPENSSL_free(ss->ext.tick);
#ifndef OPENSSL_NO_PSK
    OPENSSL_free(ss->psk_identity_hint);
    OPENSSL_free(ss->psk_identity);
#endif
#ifndef OPENSSL_NO_SRP
    OPENSSL_free(ss->srp_username);
#endif
    OPENSSL_free(ss->ext.alpn_selected);
    OPENSSL_free(ss->ticket_appdata);
    CRYPTO_THREAD_lock_free(ss->lock);
    OPENSSL_clear_free(ss, sizeof(*ss));
}

int SSL_SESSION_up_ref(SSL_SESSION *ss)
{
    int i;

    if (CRYPTO_UP_REF(&ss->references, &i, ss->lock) <= 0)
        return 0;

    REF_PRINT_COUNT("SSL_SESSION", ss);
    REF_ASSERT_ISNT(i < 2);
    return ((i > 1) ? 1 : 0);
}

int SSL_set_session(SSL *s, SSL_SESSION *session)
{
    ssl_clear_bad_session(s);
    if (s->ctx->method != s->method) {
        if (!SSL_set_ssl_method(s, s->ctx->method))
            return 0;
    }

    if (session != NULL) {
        SSL_SESSION_up_ref(session);
        s->verify_result = session->verify_result;
    }
    SSL_SESSION_free(s->session);
    s->session = session;

    return 1;
}

int SSL_SESSION_set1_id(SSL_SESSION *s, const unsigned char *sid,
                        unsigned int sid_len)
{
    if (sid_len > SSL_MAX_SSL_SESSION_ID_LENGTH) {
      ERR_raise(ERR_LIB_SSL, SSL_R_SSL_SESSION_ID_TOO_LONG);
      return 0;
    }
    s->session_id_length = sid_len;
    if (sid != s->session_id)
        memcpy(s->session_id, sid, sid_len);
    return 1;
}

long SSL_SESSION_set_timeout(SSL_SESSION *s, long t)
{
    time_t new_timeout = (time_t)t;

    if (s == NULL || t < 0)
        return 0;
    if (s->owner != NULL) {
        if (!CRYPTO_THREAD_write_lock(s->owner->lock))
            return 0;
        s->timeout = new_timeout;
        ssl_session_calculate_timeout(s);
        SSL_SESSION_list_add(s->owner, s);
        CRYPTO_THREAD_unlock(s->owner->lock);
    } else {
        s->timeout = new_timeout;
        ssl_session_calculate_timeout(s);
    }
    return 1;
}

long SSL_SESSION_get_timeout(const SSL_SESSION *s)
{
    if (s == NULL)
        return 0;
    return (long)s->timeout;
}

long SSL_SESSION_get_time(const SSL_SESSION *s)
{
    if (s == NULL)
        return 0;
    return (long)s->time;
}

long SSL_SESSION_set_time(SSL_SESSION *s, long t)
{
    time_t new_time = (time_t)t;

    if (s == NULL)
        return 0;
    if (s->owner != NULL) {
        if (!CRYPTO_THREAD_write_lock(s->owner->lock))
            return 0;
        s->time = new_time;
        ssl_session_calculate_timeout(s);
        SSL_SESSION_list_add(s->owner, s);
        CRYPTO_THREAD_unlock(s->owner->lock);
    } else {
        s->time = new_time;
        ssl_session_calculate_timeout(s);
    }
    return t;
}

int SSL_SESSION_get_protocol_version(const SSL_SESSION *s)
{
    return s->ssl_version;
}

int SSL_SESSION_set_protocol_version(SSL_SESSION *s, int version)
{
    s->ssl_version = version;
    return 1;
}

const SSL_CIPHER *SSL_SESSION_get0_cipher(const SSL_SESSION *s)
{
    return s->cipher;
}

int SSL_SESSION_set_cipher(SSL_SESSION *s, const SSL_CIPHER *cipher)
{
    s->cipher = cipher;
    return 1;
}

const char *SSL_SESSION_get0_hostname(const SSL_SESSION *s)
{
    return s->ext.hostname;
}

int SSL_SESSION_set1_hostname(SSL_SESSION *s, const char *hostname)
{
    OPENSSL_free(s->ext.hostname);
    if (hostname == NULL) {
        s->ext.hostname = NULL;
        return 1;
    }
    s->ext.hostname = OPENSSL_strdup(hostname);

    return s->ext.hostname != NULL;
}

int SSL_SESSION_has_ticket(const SSL_SESSION *s)
{
    return (s->ext.ticklen > 0) ? 1 : 0;
}

unsigned long SSL_SESSION_get_ticket_lifetime_hint(const SSL_SESSION *s)
{
    return s->ext.tick_lifetime_hint;
}

void SSL_SESSION_get0_ticket(const SSL_SESSION *s, const unsigned char **tick,
                             size_t *len)
{
    *len = s->ext.ticklen;
    if (tick != NULL)
        *tick = s->ext.tick;
}

uint32_t SSL_SESSION_get_max_early_data(const SSL_SESSION *s)
{
    return s->ext.max_early_data;
}

int SSL_SESSION_set_max_early_data(SSL_SESSION *s, uint32_t max_early_data)
{
    s->ext.max_early_data = max_early_data;

    return 1;
}

void SSL_SESSION_get0_alpn_selected(const SSL_SESSION *s,
                                    const unsigned char **alpn,
                                    size_t *len)
{
    *alpn = s->ext.alpn_selected;
    *len = s->ext.alpn_selected_len;
}

int SSL_SESSION_set1_alpn_selected(SSL_SESSION *s, const unsigned char *alpn,
                                   size_t len)
{
    OPENSSL_free(s->ext.alpn_selected);
    if (alpn == NULL || len == 0) {
        s->ext.alpn_selected = NULL;
        s->ext.alpn_selected_len = 0;
        return 1;
    }
    s->ext.alpn_selected = OPENSSL_memdup(alpn, len);
    if (s->ext.alpn_selected == NULL) {
        s->ext.alpn_selected_len = 0;
        return 0;
    }
    s->ext.alpn_selected_len = len;

    return 1;
}

X509 *SSL_SESSION_get0_peer(SSL_SESSION *s)
{
    return s->peer;
}

int SSL_SESSION_set1_id_context(SSL_SESSION *s, const unsigned char *sid_ctx,
                                unsigned int sid_ctx_len)
{
    if (sid_ctx_len > SSL_MAX_SID_CTX_LENGTH) {
        ERR_raise(ERR_LIB_SSL, SSL_R_SSL_SESSION_ID_CONTEXT_TOO_LONG);
        return 0;
    }
    s->sid_ctx_length = sid_ctx_len;
    if (sid_ctx != s->sid_ctx)
        memcpy(s->sid_ctx, sid_ctx, sid_ctx_len);

    return 1;
}

int SSL_SESSION_is_resumable(const SSL_SESSION *s)
{
    /*
     * In the case of EAP-FAST, we can have a pre-shared "ticket" without a
     * session ID.
     */
    return !s->not_resumable
           && (s->session_id_length > 0 || s->ext.ticklen > 0);
}

long SSL_CTX_set_timeout(SSL_CTX *s, long t)
{
    long l;
    if (s == NULL)
        return 0;
    l = s->session_timeout;
    s->session_timeout = t;
    return l;
}

long SSL_CTX_get_timeout(const SSL_CTX *s)
{
    if (s == NULL)
        return 0;
    return s->session_timeout;
}

int SSL_set_session_secret_cb(SSL *s,
                              tls_session_secret_cb_fn tls_session_secret_cb,
                              void *arg)
{
    if (s == NULL)
        return 0;
    s->ext.session_secret_cb = tls_session_secret_cb;
    s->ext.session_secret_cb_arg = arg;
    return 1;
}

int SSL_set_session_ticket_ext_cb(SSL *s, tls_session_ticket_ext_cb_fn cb,
                                  void *arg)
{
    if (s == NULL)
        return 0;
    s->ext.session_ticket_cb = cb;
    s->ext.session_ticket_cb_arg = arg;
    return 1;
}

int SSL_set_session_ticket_ext(SSL *s, void *ext_data, int ext_len)
{
    if (s->version >= TLS1_VERSION) {
        OPENSSL_free(s->ext.session_ticket);
        s->ext.session_ticket = NULL;
        s->ext.session_ticket =
            OPENSSL_malloc(sizeof(TLS_SESSION_TICKET_EXT) + ext_len);
        if (s->ext.session_ticket == NULL) {
            ERR_raise(ERR_LIB_SSL, ERR_R_MALLOC_FAILURE);
            return 0;
        }

        if (ext_data != NULL) {
            s->ext.session_ticket->length = ext_len;
            s->ext.session_ticket->data = s->ext.session_ticket + 1;
            memcpy(s->ext.session_ticket->data, ext_data, ext_len);
        } else {
            s->ext.session_ticket->length = 0;
            s->ext.session_ticket->data = NULL;
        }

        return 1;
    }

    return 0;
}

void SSL_CTX_flush_sessions(SSL_CTX *s, long t)
{
    STACK_OF(SSL_SESSION) *sk;
    SSL_SESSION *current;
    unsigned long i;

    if (!CRYPTO_THREAD_write_lock(s->lock))
        return;

    sk = sk_SSL_SESSION_new_null();
    i = lh_SSL_SESSION_get_down_load(s->sessions);
    lh_SSL_SESSION_set_down_load(s->sessions, 0);

    /*
     * Iterate over the list from the back (oldest), and stop
     * when a session can no longer be removed.
     * Add the session to a temporary list to be freed outside
     * the SSL_CTX lock.
     * But still do the remove_session_cb() within the lock.
     */
    while (s->session_cache_tail != NULL) {
        current = s->session_cache_tail;
        if (t == 0 || sess_timedout((time_t)t, current)) {
            lh_SSL_SESSION_delete(s->sessions, current);
            SSL_SESSION_list_remove(s, current);
            current->not_resumable = 1;
            if (s->remove_session_cb != NULL)
                s->remove_session_cb(s, current);
            /*
             * Throw the session on a stack, it's entirely plausible
             * that while freeing outside the critical section, the
             * session could be re-added, so avoid using the next/prev
             * pointers. If the stack failed to create, or the session
             * couldn't be put on the stack, just free it here
             */
            if (sk == NULL || !sk_SSL_SESSION_push(sk, current))
                SSL_SESSION_free(current);
        } else {
            break;
        }
    }

    lh_SSL_SESSION_set_down_load(s->sessions, i);
    CRYPTO_THREAD_unlock(s->lock);

    sk_SSL_SESSION_pop_free(sk, SSL_SESSION_free);
}

int ssl_clear_bad_session(SSL *s)
{
    if ((s->session != NULL) &&
        !(s->shutdown & SSL_SENT_SHUTDOWN) &&
        !(SSL_in_init(s) || SSL_in_before(s))) {
        SSL_CTX_remove_session(s->session_ctx, s->session);
        return 1;
    } else
        return 0;
}

/* locked by SSL_CTX in the calling function */
static void SSL_SESSION_list_remove(SSL_CTX *ctx, SSL_SESSION *s)
{
    if ((s->next == NULL) || (s->prev == NULL))
        return;

    if (s->next == (SSL_SESSION *)&(ctx->session_cache_tail)) {
        /* last element in list */
        if (s->prev == (SSL_SESSION *)&(ctx->session_cache_head)) {
            /* only one element in list */
            ctx->session_cache_head = NULL;
            ctx->session_cache_tail = NULL;
        } else {
            ctx->session_cache_tail = s->prev;
            s->prev->next = (SSL_SESSION *)&(ctx->session_cache_tail);
        }
    } else {
        if (s->prev == (SSL_SESSION *)&(ctx->session_cache_head)) {
            /* first element in list */
            ctx->session_cache_head = s->next;
            s->next->prev = (SSL_SESSION *)&(ctx->session_cache_head);
        } else {
            /* middle of list */
            s->next->prev = s->prev;
            s->prev->next = s->next;
        }
    }
    s->prev = s->next = NULL;
    s->owner = NULL;
}

static void SSL_SESSION_list_add(SSL_CTX *ctx, SSL_SESSION *s)
{
    SSL_SESSION *next;

    if ((s->next != NULL) && (s->prev != NULL))
        SSL_SESSION_list_remove(ctx, s);

    if (ctx->session_cache_head == NULL) {
        ctx->session_cache_head = s;
        ctx->session_cache_tail = s;
        s->prev = (SSL_SESSION *)&(ctx->session_cache_head);
        s->next = (SSL_SESSION *)&(ctx->session_cache_tail);
    } else {
        if (timeoutcmp(s, ctx->session_cache_head) >= 0) {
            /*
             * if we timeout after (or the same time as) the first
             * session, put us first - usual case
             */
            s->next = ctx->session_cache_head;
            s->next->prev = s;
            s->prev = (SSL_SESSION *)&(ctx->session_cache_head);
            ctx->session_cache_head = s;
        } else if (timeoutcmp(s, ctx->session_cache_tail) < 0) {
            /* if we timeout before the last session, put us last */
            s->prev = ctx->session_cache_tail;
            s->prev->next = s;
            s->next = (SSL_SESSION *)&(ctx->session_cache_tail);
            ctx->session_cache_tail = s;
        } else {
            /*
             * we timeout somewhere in-between - if there is only
             * one session in the cache it will be caught above
             */
            next = ctx->session_cache_head->next;
            while (next != (SSL_SESSION*)&(ctx->session_cache_tail)) {
                if (timeoutcmp(s, next) >= 0) {
                    s->next = next;
                    s->prev = next->prev;
                    next->prev->next = s;
                    next->prev = s;
                    break;
                }
                next = next->next;
            }
        }
    }
    s->owner = ctx;
}

void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx,
                             int (*cb) (struct ssl_st *ssl, SSL_SESSION *sess))
{
    ctx->new_session_cb = cb;
}

int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx)) (SSL *ssl, SSL_SESSION *sess) {
    return ctx->new_session_cb;
}

void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx,
                                void (*cb) (SSL_CTX *ctx, SSL_SESSION *sess))
{
    ctx->remove_session_cb = cb;
}

void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx)) (SSL_CTX *ctx,
                                                  SSL_SESSION *sess) {
    return ctx->remove_session_cb;
}

void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx,
                             SSL_SESSION *(*cb) (struct ssl_st *ssl,
                                                 const unsigned char *data,
                                                 int len, int *copy))
{
    ctx->get_session_cb = cb;
}

SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx)) (SSL *ssl,
                                                       const unsigned char
                                                       *data, int len,
                                                       int *copy) {
    return ctx->get_session_cb;
}

void SSL_CTX_set_info_callback(SSL_CTX *ctx,
                               void (*cb) (const SSL *ssl, int type, int val))
{
    ctx->info_callback = cb;
}

void (*SSL_CTX_get_info_callback(SSL_CTX *ctx)) (const SSL *ssl, int type,
                                                 int val) {
    return ctx->info_callback;
}

void SSL_CTX_set_client_cert_cb(SSL_CTX *ctx,
                                int (*cb) (SSL *ssl, X509 **x509,
                                           EVP_PKEY **pkey))
{
    ctx->client_cert_cb = cb;
}

int (*SSL_CTX_get_client_cert_cb(SSL_CTX *ctx)) (SSL *ssl, X509 **x509,
                                                 EVP_PKEY **pkey) {
    return ctx->client_cert_cb;
}

void SSL_CTX_set_cookie_generate_cb(SSL_CTX *ctx,
                                    int (*cb) (SSL *ssl,
                                               unsigned char *cookie,
                                               unsigned int *cookie_len))
{
    ctx->app_gen_cookie_cb = cb;
}

void SSL_CTX_set_cookie_verify_cb(SSL_CTX *ctx,
                                  int (*cb) (SSL *ssl,
                                             const unsigned char *cookie,
                                             unsigned int cookie_len))
{
    ctx->app_verify_cookie_cb = cb;
}

int SSL_SESSION_set1_ticket_appdata(SSL_SESSION *ss, const void *data, size_t len)
{
    OPENSSL_free(ss->ticket_appdata);
    ss->ticket_appdata_len = 0;
    if (data == NULL || len == 0) {
        ss->ticket_appdata = NULL;
        return 1;
    }
    ss->ticket_appdata = OPENSSL_memdup(data, len);
    if (ss->ticket_appdata != NULL) {
        ss->ticket_appdata_len = len;
        return 1;
    }
    return 0;
}

int SSL_SESSION_get0_ticket_appdata(SSL_SESSION *ss, void **data, size_t *len)
{
    *data = ss->ticket_appdata;
    *len = ss->ticket_appdata_len;
    return 1;
}

void SSL_CTX_set_stateless_cookie_generate_cb(
    SSL_CTX *ctx,
    int (*cb) (SSL *ssl,
               unsigned char *cookie,
               size_t *cookie_len))
{
    ctx->gen_stateless_cookie_cb = cb;
}

void SSL_CTX_set_stateless_cookie_verify_cb(
    SSL_CTX *ctx,
    int (*cb) (SSL *ssl,
               const unsigned char *cookie,
               size_t cookie_len))
{
    ctx->verify_stateless_cookie_cb = cb;
}

IMPLEMENT_PEM_rw(SSL_SESSION, SSL_SESSION, PEM_STRING_SSL_SESSION, SSL_SESSION)