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view src/mail/ngx_mail_ssl_module.c @ 7729:3bff3f397c05

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SSL: ssl_conf_command directive. With the ssl_conf_command directive it is now possible to set arbitrary OpenSSL configuration parameters as long as nginx is compiled with OpenSSL 1.0.2 or later. Full list of available configuration commands can be found in the SSL_CONF_cmd manual page (https://www.openssl.org/docs/man1.1.1/man3/SSL_CONF_cmd.html). In particular, this allows configuring PrioritizeChaCha option (ticket #1445): ssl_conf_command Options PrioritizeChaCha; It can be also used to configure TLSv1.3 ciphers in OpenSSL, which fails to configure them via the SSL_CTX_set_cipher_list() interface (ticket #1529): ssl_conf_command Ciphersuites TLS_CHACHA20_POLY1305_SHA256; Configuration commands are applied after nginx own configuration for SSL, so they can be used to override anything set by nginx. Note though that configuring OpenSSL directly with ssl_conf_command might result in a behaviour nginx does not expect, and should be done with care.
author Maxim Dounin <mdounin@mdounin.ru>
date Thu, 22 Oct 2020 18:00:22 +0300
parents ef7ee19776db
children 7ce28b4cc57e
line wrap: on
line source


/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_mail.h>


#define NGX_DEFAULT_CIPHERS     "HIGH:!aNULL:!MD5"
#define NGX_DEFAULT_ECDH_CURVE  "auto"


static void *ngx_mail_ssl_create_conf(ngx_conf_t *cf);
static char *ngx_mail_ssl_merge_conf(ngx_conf_t *cf, void *parent, void *child);

static char *ngx_mail_ssl_enable(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);
static char *ngx_mail_ssl_starttls(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);
static char *ngx_mail_ssl_password_file(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);
static char *ngx_mail_ssl_session_cache(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);

static char *ngx_mail_ssl_conf_command_check(ngx_conf_t *cf, void *post,
    void *data);


static ngx_conf_enum_t  ngx_mail_starttls_state[] = {
    { ngx_string("off"), NGX_MAIL_STARTTLS_OFF },
    { ngx_string("on"), NGX_MAIL_STARTTLS_ON },
    { ngx_string("only"), NGX_MAIL_STARTTLS_ONLY },
    { ngx_null_string, 0 }
};



static ngx_conf_bitmask_t  ngx_mail_ssl_protocols[] = {
    { ngx_string("SSLv2"), NGX_SSL_SSLv2 },
    { ngx_string("SSLv3"), NGX_SSL_SSLv3 },
    { ngx_string("TLSv1"), NGX_SSL_TLSv1 },
    { ngx_string("TLSv1.1"), NGX_SSL_TLSv1_1 },
    { ngx_string("TLSv1.2"), NGX_SSL_TLSv1_2 },
    { ngx_string("TLSv1.3"), NGX_SSL_TLSv1_3 },
    { ngx_null_string, 0 }
};


static ngx_conf_enum_t  ngx_mail_ssl_verify[] = {
    { ngx_string("off"), 0 },
    { ngx_string("on"), 1 },
    { ngx_string("optional"), 2 },
    { ngx_string("optional_no_ca"), 3 },
    { ngx_null_string, 0 }
};


static ngx_conf_deprecated_t  ngx_mail_ssl_deprecated = {
    ngx_conf_deprecated, "ssl", "listen ... ssl"
};


static ngx_conf_post_t  ngx_mail_ssl_conf_command_post =
    { ngx_mail_ssl_conf_command_check };


static ngx_command_t  ngx_mail_ssl_commands[] = {

    { ngx_string("ssl"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_mail_ssl_enable,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, enable),
      &ngx_mail_ssl_deprecated },

    { ngx_string("starttls"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_mail_ssl_starttls,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, starttls),
      ngx_mail_starttls_state },

    { ngx_string("ssl_certificate"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_array_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, certificates),
      NULL },

    { ngx_string("ssl_certificate_key"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_array_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, certificate_keys),
      NULL },

    { ngx_string("ssl_password_file"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_mail_ssl_password_file,
      NGX_MAIL_SRV_CONF_OFFSET,
      0,
      NULL },

    { ngx_string("ssl_dhparam"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, dhparam),
      NULL },

    { ngx_string("ssl_ecdh_curve"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, ecdh_curve),
      NULL },

    { ngx_string("ssl_protocols"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_1MORE,
      ngx_conf_set_bitmask_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, protocols),
      &ngx_mail_ssl_protocols },

    { ngx_string("ssl_ciphers"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, ciphers),
      NULL },

    { ngx_string("ssl_prefer_server_ciphers"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, prefer_server_ciphers),
      NULL },

    { ngx_string("ssl_session_cache"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE12,
      ngx_mail_ssl_session_cache,
      NGX_MAIL_SRV_CONF_OFFSET,
      0,
      NULL },

    { ngx_string("ssl_session_tickets"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, session_tickets),
      NULL },

    { ngx_string("ssl_session_ticket_key"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_array_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, session_ticket_keys),
      NULL },

    { ngx_string("ssl_session_timeout"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_sec_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, session_timeout),
      NULL },

    { ngx_string("ssl_verify_client"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_enum_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, verify),
      &ngx_mail_ssl_verify },

    { ngx_string("ssl_verify_depth"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_num_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, verify_depth),
      NULL },

    { ngx_string("ssl_client_certificate"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, client_certificate),
      NULL },

    { ngx_string("ssl_trusted_certificate"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, trusted_certificate),
      NULL },

    { ngx_string("ssl_crl"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, crl),
      NULL },

    { ngx_string("ssl_conf_command"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE2,
      ngx_conf_set_keyval_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_ssl_conf_t, conf_commands),
      &ngx_mail_ssl_conf_command_post },

      ngx_null_command
};


static ngx_mail_module_t  ngx_mail_ssl_module_ctx = {
    NULL,                                  /* protocol */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    ngx_mail_ssl_create_conf,              /* create server configuration */
    ngx_mail_ssl_merge_conf                /* merge server configuration */
};


ngx_module_t  ngx_mail_ssl_module = {
    NGX_MODULE_V1,
    &ngx_mail_ssl_module_ctx,              /* module context */
    ngx_mail_ssl_commands,                 /* module directives */
    NGX_MAIL_MODULE,                       /* module type */
    NULL,                                  /* init master */
    NULL,                                  /* init module */
    NULL,                                  /* init process */
    NULL,                                  /* init thread */
    NULL,                                  /* exit thread */
    NULL,                                  /* exit process */
    NULL,                                  /* exit master */
    NGX_MODULE_V1_PADDING
};


static ngx_str_t ngx_mail_ssl_sess_id_ctx = ngx_string("MAIL");


static void *
ngx_mail_ssl_create_conf(ngx_conf_t *cf)
{
    ngx_mail_ssl_conf_t  *scf;

    scf = ngx_pcalloc(cf->pool, sizeof(ngx_mail_ssl_conf_t));
    if (scf == NULL) {
        return NULL;
    }

    /*
     * set by ngx_pcalloc():
     *
     *     scf->listen = 0;
     *     scf->protocols = 0;
     *     scf->dhparam = { 0, NULL };
     *     scf->ecdh_curve = { 0, NULL };
     *     scf->client_certificate = { 0, NULL };
     *     scf->trusted_certificate = { 0, NULL };
     *     scf->crl = { 0, NULL };
     *     scf->ciphers = { 0, NULL };
     *     scf->shm_zone = NULL;
     */

    scf->enable = NGX_CONF_UNSET;
    scf->starttls = NGX_CONF_UNSET_UINT;
    scf->certificates = NGX_CONF_UNSET_PTR;
    scf->certificate_keys = NGX_CONF_UNSET_PTR;
    scf->passwords = NGX_CONF_UNSET_PTR;
    scf->conf_commands = NGX_CONF_UNSET_PTR;
    scf->prefer_server_ciphers = NGX_CONF_UNSET;
    scf->verify = NGX_CONF_UNSET_UINT;
    scf->verify_depth = NGX_CONF_UNSET_UINT;
    scf->builtin_session_cache = NGX_CONF_UNSET;
    scf->session_timeout = NGX_CONF_UNSET;
    scf->session_tickets = NGX_CONF_UNSET;
    scf->session_ticket_keys = NGX_CONF_UNSET_PTR;

    return scf;
}


static char *
ngx_mail_ssl_merge_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_mail_ssl_conf_t *prev = parent;
    ngx_mail_ssl_conf_t *conf = child;

    char                *mode;
    ngx_pool_cleanup_t  *cln;

    ngx_conf_merge_value(conf->enable, prev->enable, 0);
    ngx_conf_merge_uint_value(conf->starttls, prev->starttls,
                         NGX_MAIL_STARTTLS_OFF);

    ngx_conf_merge_value(conf->session_timeout,
                         prev->session_timeout, 300);

    ngx_conf_merge_value(conf->prefer_server_ciphers,
                         prev->prefer_server_ciphers, 0);

    ngx_conf_merge_bitmask_value(conf->protocols, prev->protocols,
                         (NGX_CONF_BITMASK_SET|NGX_SSL_TLSv1
                          |NGX_SSL_TLSv1_1|NGX_SSL_TLSv1_2));

    ngx_conf_merge_uint_value(conf->verify, prev->verify, 0);
    ngx_conf_merge_uint_value(conf->verify_depth, prev->verify_depth, 1);

    ngx_conf_merge_ptr_value(conf->certificates, prev->certificates, NULL);
    ngx_conf_merge_ptr_value(conf->certificate_keys, prev->certificate_keys,
                         NULL);

    ngx_conf_merge_ptr_value(conf->passwords, prev->passwords, NULL);

    ngx_conf_merge_str_value(conf->dhparam, prev->dhparam, "");

    ngx_conf_merge_str_value(conf->ecdh_curve, prev->ecdh_curve,
                         NGX_DEFAULT_ECDH_CURVE);

    ngx_conf_merge_str_value(conf->client_certificate,
                         prev->client_certificate, "");
    ngx_conf_merge_str_value(conf->trusted_certificate,
                         prev->trusted_certificate, "");
    ngx_conf_merge_str_value(conf->crl, prev->crl, "");

    ngx_conf_merge_str_value(conf->ciphers, prev->ciphers, NGX_DEFAULT_CIPHERS);

    ngx_conf_merge_ptr_value(conf->conf_commands, prev->conf_commands, NULL);


    conf->ssl.log = cf->log;

    if (conf->listen) {
        mode = "listen ... ssl";

    } else if (conf->enable) {
        mode = "ssl";

    } else if (conf->starttls != NGX_MAIL_STARTTLS_OFF) {
        mode = "starttls";

    } else {
        return NGX_CONF_OK;
    }

    if (conf->file == NULL) {
        conf->file = prev->file;
        conf->line = prev->line;
    }

    if (conf->certificates == NULL) {
        ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                      "no \"ssl_certificate\" is defined for "
                      "the \"%s\" directive in %s:%ui",
                      mode, conf->file, conf->line);
        return NGX_CONF_ERROR;
    }

    if (conf->certificate_keys == NULL) {
        ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                      "no \"ssl_certificate_key\" is defined for "
                      "the \"%s\" directive in %s:%ui",
                      mode, conf->file, conf->line);
        return NGX_CONF_ERROR;
    }

    if (conf->certificate_keys->nelts < conf->certificates->nelts) {
        ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                      "no \"ssl_certificate_key\" is defined "
                      "for certificate \"%V\" and "
                      "the \"%s\" directive in %s:%ui",
                      ((ngx_str_t *) conf->certificates->elts)
                      + conf->certificates->nelts - 1,
                      mode, conf->file, conf->line);
        return NGX_CONF_ERROR;
    }

    if (ngx_ssl_create(&conf->ssl, conf->protocols, NULL) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

    cln = ngx_pool_cleanup_add(cf->pool, 0);
    if (cln == NULL) {
        ngx_ssl_cleanup_ctx(&conf->ssl);
        return NGX_CONF_ERROR;
    }

    cln->handler = ngx_ssl_cleanup_ctx;
    cln->data = &conf->ssl;

    if (ngx_ssl_certificates(cf, &conf->ssl, conf->certificates,
                             conf->certificate_keys, conf->passwords)
        != NGX_OK)
    {
        return NGX_CONF_ERROR;
    }

    if (conf->verify) {

        if (conf->client_certificate.len == 0 && conf->verify != 3) {
            ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                          "no ssl_client_certificate for ssl_verify_client");
            return NGX_CONF_ERROR;
        }

        if (ngx_ssl_client_certificate(cf, &conf->ssl,
                                       &conf->client_certificate,
                                       conf->verify_depth)
            != NGX_OK)
        {
            return NGX_CONF_ERROR;
        }

        if (ngx_ssl_trusted_certificate(cf, &conf->ssl,
                                        &conf->trusted_certificate,
                                        conf->verify_depth)
            != NGX_OK)
        {
            return NGX_CONF_ERROR;
        }

        if (ngx_ssl_crl(cf, &conf->ssl, &conf->crl) != NGX_OK) {
            return NGX_CONF_ERROR;
        }
    }

    if (ngx_ssl_ciphers(cf, &conf->ssl, &conf->ciphers,
                        conf->prefer_server_ciphers)
        != NGX_OK)
    {
        return NGX_CONF_ERROR;
    }

    if (ngx_ssl_dhparam(cf, &conf->ssl, &conf->dhparam) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

    if (ngx_ssl_ecdh_curve(cf, &conf->ssl, &conf->ecdh_curve) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

    ngx_conf_merge_value(conf->builtin_session_cache,
                         prev->builtin_session_cache, NGX_SSL_NONE_SCACHE);

    if (conf->shm_zone == NULL) {
        conf->shm_zone = prev->shm_zone;
    }

    if (ngx_ssl_session_cache(&conf->ssl, &ngx_mail_ssl_sess_id_ctx,
                              conf->certificates, conf->builtin_session_cache,
                              conf->shm_zone, conf->session_timeout)
        != NGX_OK)
    {
        return NGX_CONF_ERROR;
    }

    ngx_conf_merge_value(conf->session_tickets,
                         prev->session_tickets, 1);

#ifdef SSL_OP_NO_TICKET
    if (!conf->session_tickets) {
        SSL_CTX_set_options(conf->ssl.ctx, SSL_OP_NO_TICKET);
    }
#endif

    ngx_conf_merge_ptr_value(conf->session_ticket_keys,
                         prev->session_ticket_keys, NULL);

    if (ngx_ssl_session_ticket_keys(cf, &conf->ssl, conf->session_ticket_keys)
        != NGX_OK)
    {
        return NGX_CONF_ERROR;
    }

    if (ngx_ssl_conf_commands(cf, &conf->ssl, conf->conf_commands) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

    return NGX_CONF_OK;
}


static char *
ngx_mail_ssl_enable(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_mail_ssl_conf_t  *scf = conf;

    char  *rv;

    rv = ngx_conf_set_flag_slot(cf, cmd, conf);

    if (rv != NGX_CONF_OK) {
        return rv;
    }

    if (scf->enable && (ngx_int_t) scf->starttls > NGX_MAIL_STARTTLS_OFF) {
        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "\"starttls\" directive conflicts with \"ssl on\"");
        return NGX_CONF_ERROR;
    }

    if (!scf->listen) {
        scf->file = cf->conf_file->file.name.data;
        scf->line = cf->conf_file->line;
    }

    return NGX_CONF_OK;
}


static char *
ngx_mail_ssl_starttls(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_mail_ssl_conf_t  *scf = conf;

    char  *rv;

    rv = ngx_conf_set_enum_slot(cf, cmd, conf);

    if (rv != NGX_CONF_OK) {
        return rv;
    }

    if (scf->enable == 1 && (ngx_int_t) scf->starttls > NGX_MAIL_STARTTLS_OFF) {
        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "\"ssl\" directive conflicts with \"starttls\"");
        return NGX_CONF_ERROR;
    }

    if (!scf->listen) {
        scf->file = cf->conf_file->file.name.data;
        scf->line = cf->conf_file->line;
    }

    return NGX_CONF_OK;
}


static char *
ngx_mail_ssl_password_file(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_mail_ssl_conf_t  *scf = conf;

    ngx_str_t  *value;

    if (scf->passwords != NGX_CONF_UNSET_PTR) {
        return "is duplicate";
    }

    value = cf->args->elts;

    scf->passwords = ngx_ssl_read_password_file(cf, &value[1]);

    if (scf->passwords == NULL) {
        return NGX_CONF_ERROR;
    }

    return NGX_CONF_OK;
}


static char *
ngx_mail_ssl_session_cache(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_mail_ssl_conf_t  *scf = conf;

    size_t       len;
    ngx_str_t   *value, name, size;
    ngx_int_t    n;
    ngx_uint_t   i, j;

    value = cf->args->elts;

    for (i = 1; i < cf->args->nelts; i++) {

        if (ngx_strcmp(value[i].data, "off") == 0) {
            scf->builtin_session_cache = NGX_SSL_NO_SCACHE;
            continue;
        }

        if (ngx_strcmp(value[i].data, "none") == 0) {
            scf->builtin_session_cache = NGX_SSL_NONE_SCACHE;
            continue;
        }

        if (ngx_strcmp(value[i].data, "builtin") == 0) {
            scf->builtin_session_cache = NGX_SSL_DFLT_BUILTIN_SCACHE;
            continue;
        }

        if (value[i].len > sizeof("builtin:") - 1
            && ngx_strncmp(value[i].data, "builtin:", sizeof("builtin:") - 1)
               == 0)
        {
            n = ngx_atoi(value[i].data + sizeof("builtin:") - 1,
                         value[i].len - (sizeof("builtin:") - 1));

            if (n == NGX_ERROR) {
                goto invalid;
            }

            scf->builtin_session_cache = n;

            continue;
        }

        if (value[i].len > sizeof("shared:") - 1
            && ngx_strncmp(value[i].data, "shared:", sizeof("shared:") - 1)
               == 0)
        {
            len = 0;

            for (j = sizeof("shared:") - 1; j < value[i].len; j++) {
                if (value[i].data[j] == ':') {
                    break;
                }

                len++;
            }

            if (len == 0) {
                goto invalid;
            }

            name.len = len;
            name.data = value[i].data + sizeof("shared:") - 1;

            size.len = value[i].len - j - 1;
            size.data = name.data + len + 1;

            n = ngx_parse_size(&size);

            if (n == NGX_ERROR) {
                goto invalid;
            }

            if (n < (ngx_int_t) (8 * ngx_pagesize)) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "session cache \"%V\" is too small",
                                   &value[i]);

                return NGX_CONF_ERROR;
            }

            scf->shm_zone = ngx_shared_memory_add(cf, &name, n,
                                                   &ngx_mail_ssl_module);
            if (scf->shm_zone == NULL) {
                return NGX_CONF_ERROR;
            }

            scf->shm_zone->init = ngx_ssl_session_cache_init;

            continue;
        }

        goto invalid;
    }

    if (scf->shm_zone && scf->builtin_session_cache == NGX_CONF_UNSET) {
        scf->builtin_session_cache = NGX_SSL_NO_BUILTIN_SCACHE;
    }

    return NGX_CONF_OK;

invalid:

    ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                       "invalid session cache \"%V\"", &value[i]);

    return NGX_CONF_ERROR;
}


static char *
ngx_mail_ssl_conf_command_check(ngx_conf_t *cf, void *post, void *data)
{
#ifndef SSL_CONF_FLAG_FILE
    return "is not supported on this platform";
#endif

    return NGX_CONF_OK;
}