lighttpd1.4/src/mod_openssl.c

/*
 * mod_openssl - openssl support for lighttpd
 */
/*
 * future possible enhancements: OCSP stapling
 *
 * Note: If session tickets are -not- disabled with
 *     ssl.openssl.ssl-conf-cmd = ("Options" => "-SessionTicket")
 *   mod_openssl rotates server ticket encryption key (STEK) every 24 hours.
 *   This is fine for use with a single lighttpd instance, but with multiple
 *   lighttpd workers, no coordinated STEK (server ticket encryption key)
 *   rotation occurs other than by (some external job) restarting lighttpd.
 *   Restarting lighttpd generates a new key that is shared by lighttpd workers
 *   for the lifetime of the new key.  If the rotation period expires and
 *   lighttpd has not been restarted, lighttpd workers will generate new
 *   independent keys, making session tickets less effective for session
 *   resumption, since clients have a lower chance for future connections to
 *   reach the same lighttpd worker.  However, things will still work, and a new
 *   session will be created if session resumption fails.  Admins should plan to
 *   restart lighttpd at least every 24 hours if session tickets are enabled and
 *   multiple lighttpd workers are configured.
 */
#include "first.h"

#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifndef USE_OPENSSL_KERBEROS
#ifndef OPENSSL_NO_KRB5
#define OPENSSL_NO_KRB5
#endif
#endif

#include "sys-crypto.h"

#include <openssl/ssl.h>
#include <openssl/bio.h>
#include <openssl/bn.h>
#include <openssl/err.h>
#include <openssl/objects.h>
#include <openssl/pem.h>
#include <openssl/rand.h>
#ifndef OPENSSL_NO_DH
#include <openssl/dh.h>
#endif

#if ! defined OPENSSL_NO_TLSEXT && ! defined SSL_CTRL_SET_TLSEXT_HOSTNAME
#define OPENSSL_NO_TLSEXT
#endif

#if OPENSSL_VERSION_NUMBER >= 0x0090800fL
#ifndef OPENSSL_NO_ECDH
#include <openssl/ecdh.h>
#endif
#endif

#include "base.h"
#include "http_header.h"
#include "log.h"
#include "plugin.h"

typedef struct {
    /* SNI per host: with COMP_SERVER_SOCKET, COMP_HTTP_SCHEME, COMP_HTTP_HOST */
    EVP_PKEY *ssl_pemfile_pkey;
    X509 *ssl_pemfile_x509;
    const buffer *ssl_pemfile;
    const buffer *ssl_privkey;
} plugin_cert;

typedef struct {
    SSL_CTX *ssl_ctx;
    EVP_PKEY *ssl_pemfile_pkey;
} plugin_ssl_ctx;

typedef struct {
    SSL_CTX *ssl_ctx; /* output from network_init_ssl() */

    /*(used only during startup; not patched)*/
    unsigned char ssl_enabled; /* only interesting for setting up listening sockets. don't use at runtime */
    unsigned char ssl_honor_cipher_order; /* determine SSL cipher in server-preferred order, not client-order */
    unsigned char ssl_empty_fragments; /* whether to not set SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS */
    unsigned char ssl_use_sslv2;
    unsigned char ssl_use_sslv3;
    const buffer *ssl_cipher_list;
    const buffer *ssl_dh_file;
    const buffer *ssl_ec_curve;
    array *ssl_conf_cmd;

    /*(copied from plugin_data for socket ssl_ctx config)*/
    EVP_PKEY *ssl_pemfile_pkey;
    X509 *ssl_pemfile_x509;
    const buffer *ssl_pemfile;
    const buffer *ssl_privkey;
    STACK_OF(X509_NAME) *ssl_ca_file;
    STACK_OF(X509_NAME) *ssl_ca_dn_file;
    const buffer *ssl_ca_crl_file;
    unsigned char ssl_verifyclient;
    unsigned char ssl_verifyclient_enforce;
    unsigned char ssl_verifyclient_depth;
    unsigned char ssl_read_ahead;
} plugin_config_socket; /*(used at startup during configuration)*/

typedef struct {
    /* SNI per host: w/ COMP_SERVER_SOCKET, COMP_HTTP_SCHEME, COMP_HTTP_HOST */
    EVP_PKEY *ssl_pemfile_pkey;
    X509 *ssl_pemfile_x509;
    const buffer *ssl_pemfile;
    STACK_OF(X509_NAME) *ssl_ca_file;
    STACK_OF(X509_NAME) *ssl_ca_dn_file;
    const buffer *ssl_ca_crl_file;

    unsigned char ssl_verifyclient;
    unsigned char ssl_verifyclient_enforce;
    unsigned char ssl_verifyclient_depth;
    unsigned char ssl_verifyclient_export_cert;
    unsigned char ssl_read_ahead;
    unsigned char ssl_log_noise;
    unsigned char ssl_disable_client_renegotiation;
    const buffer *ssl_verifyclient_username;
    const buffer *ssl_acme_tls_1;
} plugin_config;

typedef struct {
    PLUGIN_DATA;
    plugin_ssl_ctx *ssl_ctxs;
    plugin_config defaults;
    server *srv;
    array *cafiles;
} plugin_data;

static int ssl_is_init;
/* need assigned p->id for deep access of module handler_ctx for connection
 *   i.e. handler_ctx *hctx = r->plugin_ctx[plugin_data_singleton->id]; */
static plugin_data *plugin_data_singleton;
#define LOCAL_SEND_BUFSIZE (16 * 1024)
static char *local_send_buffer;

typedef struct {
    SSL *ssl;
    request_st *r;
    connection *con;
    short renegotiations; /* count of SSL_CB_HANDSHAKE_START */
    short close_notify;
    unsigned short request_env_patched;
    unsigned short alpn;
    plugin_config conf;
    buffer *tmp_buf;
} handler_ctx;


static handler_ctx *
handler_ctx_init (void)
{
    handler_ctx *hctx = calloc(1, sizeof(*hctx));
    force_assert(hctx);
    return hctx;
}


static void
handler_ctx_free (handler_ctx *hctx)
{
    if (hctx->ssl) SSL_free(hctx->ssl);
    free(hctx);
}


#ifdef TLSEXT_TYPE_session_ticket
static time_t stek_rotate_ts;

static void
mod_openssl_session_ticket_key_rotate (server * const srv, const plugin_data * const p)
{
    /* server ticket encryption key (STEK) is *per-SSL_CTX* in openssl
     *   and keys are initially created in SSL_CTX_new()
     * SSL_CTX_set_tlsext_ticket_keys() is an openssl interface,
     *   but how to construct its arguments is not well documented.
     * See openssl ssl/s3_lib.c
     *   case SSL_CTRL_SET_TLSEXT_TICKET_KEYS:
     * In openssl 1.1.x
     *   ssl/ssl_local.h
     *     TLSEXT_KEYNAME_LENGTH  16
     *     TLSEXT_TICK_KEY_LENGTH 32
     *   private SSL_CTX data members:
     *     ssl_ctx->ext.tick_key_name          TLSEXT_KEYNAME_LENGTH
     *     ssl_ctx->ext.secure->tick_hmac_key  TLSEXT_TICK_KEY_LENGTH
     *     ssl_ctx->ext.secure->tick_aes_key   TLSEXT_TICK_KEY_LENGTH
     * In openssl 1.0.x, each element is 16 bytes (TLSEXT_TICK_KEY_LENGTH 16)
     *
     * openssl RAND_*bytes() functions are called multiple times since the
     * funcs might have a 32-byte limit on number of bytes returned each call
     *
     * (Note: session ticket encryption key rotation is not expected to fail)
     */
    int rc = 1;
  #if OPENSSL_VERSION_NUMBER < 0x10100000L
    unsigned char keys[16+16+16];
    if (RAND_bytes(keys,16) <= 0
        || RAND_bytes(keys+16,16) <= 0
        || RAND_bytes(keys+16+16,16) <= 0)
  #else
    /*(RAND_priv_bytes() not in openssl 1.1.0; introduced in openssl 1.1.1)*/
    #if OPENSSL_VERSION_NUMBER < 0x10101000L
    #define RAND_priv_bytes(x,sz) RAND_bytes((x),(sz))
    #endif
    unsigned char keys[16+32+32];
    if (RAND_bytes(keys,16) <= 0
        || RAND_priv_bytes(keys+16,32) <= 0
        || RAND_priv_bytes(keys+16+32,32) <= 0)
  #endif
        rc = 0;

    const size_t sz = sizeof(keys);

    for (uint32_t i = 0; i < srv->config_context->used; ++i) {
        plugin_ssl_ctx * const s = p->ssl_ctxs + i;
        if (!s->ssl_ctx) continue;
        if (SSL_CTX_get_options(s->ssl_ctx) & SSL_OP_NO_TICKET) continue;
        if (!rc || 1 != SSL_CTX_set_tlsext_ticket_keys(s->ssl_ctx, keys, sz)) {
            /*(disable session tickets rather than continue to use aging keys)*/
            long opts = SSL_CTX_get_options(s->ssl_ctx) | SSL_OP_NO_TICKET;
            SSL_CTX_set_options(s->ssl_ctx, opts);
            log_error(srv->errh, __FILE__, __LINE__,
              "SSL: STEK rotation failed; disabling session tickets");
        }
    }

    OPENSSL_cleanse(keys, sizeof(keys));
}
#endif /* TLSEXT_TYPE_session_ticket */


INIT_FUNC(mod_openssl_init)
{
    plugin_data_singleton = (plugin_data *)calloc(1, sizeof(plugin_data));
  #ifdef DEBUG_WOLFSSL
    wolfSSL_Debugging_ON();
  #endif
    return plugin_data_singleton;
}


static int mod_openssl_init_once_openssl (server *srv)
{
    if (ssl_is_init) return 1;

  #if OPENSSL_VERSION_NUMBER >= 0x10100000L \
   && !defined(LIBRESSL_VERSION_NUMBER)
    OPENSSL_init_ssl(OPENSSL_INIT_LOAD_SSL_STRINGS
                    |OPENSSL_INIT_LOAD_CRYPTO_STRINGS,NULL);
    OPENSSL_init_crypto(OPENSSL_INIT_ADD_ALL_CIPHERS
                       |OPENSSL_INIT_ADD_ALL_DIGESTS
                       |OPENSSL_INIT_LOAD_CONFIG, NULL);
  #else
    SSL_load_error_strings();
    SSL_library_init();
    OpenSSL_add_all_algorithms();
  #endif
    ssl_is_init = 1;

    if (0 == RAND_status()) {
        log_error(srv->errh, __FILE__, __LINE__,
          "SSL: not enough entropy in the pool");
        return 0;
    }

    local_send_buffer = malloc(LOCAL_SEND_BUFSIZE);
    force_assert(NULL != local_send_buffer);

    return 1;
}


static void mod_openssl_free_openssl (void)
{
    if (!ssl_is_init) return;

  #if OPENSSL_VERSION_NUMBER >= 0x10100000L \
   && !defined(LIBRESSL_VERSION_NUMBER)
    /*(OpenSSL libraries handle thread init and deinit)
     * https://github.com/openssl/openssl/pull/1048 */
  #else
    CRYPTO_cleanup_all_ex_data();
    ERR_free_strings();
   #if OPENSSL_VERSION_NUMBER >= 0x10000000L
    ERR_remove_thread_state(NULL);
   #else
    ERR_remove_state(0);
   #endif
    EVP_cleanup();
  #endif

    free(local_send_buffer);
    ssl_is_init = 0;
}


static void
mod_openssl_free_config (server *srv, plugin_data * const p)
{
    array_free(p->cafiles);

    if (NULL != p->ssl_ctxs) {
        SSL_CTX * const ssl_ctx_global_scope = p->ssl_ctxs->ssl_ctx;
        /* free ssl_ctx from $SERVER["socket"] (if not copy of global scope) */
        for (uint32_t i = 1; i < srv->config_context->used; ++i) {
            plugin_ssl_ctx * const s = p->ssl_ctxs + i;
            if (s->ssl_ctx && s->ssl_ctx != ssl_ctx_global_scope)
                SSL_CTX_free(s->ssl_ctx);
        }
        /* free ssl_ctx from global scope */
        if (ssl_ctx_global_scope)
            SSL_CTX_free(ssl_ctx_global_scope);
        free(p->ssl_ctxs);
    }

    if (NULL == p->cvlist) return;
    /* (init i to 0 if global context; to 1 to skip empty global context) */
    for (int i = !p->cvlist[0].v.u2[1], used = p->nconfig; i < used; ++i) {
        config_plugin_value_t *cpv = p->cvlist + p->cvlist[i].v.u2[0];
        for (; -1 != cpv->k_id; ++cpv) {
            switch (cpv->k_id) {
              case 0: /* ssl.pemfile */
                if (cpv->vtype == T_CONFIG_LOCAL) {
                    plugin_cert *pc = cpv->v.v;
                    EVP_PKEY_free(pc->ssl_pemfile_pkey);
                    X509_free(pc->ssl_pemfile_x509);
                }
                break;
              case 2: /* ssl.ca-file */
              case 3: /* ssl.ca-dn-file */
                if (cpv->vtype == T_CONFIG_LOCAL)
                    sk_X509_NAME_pop_free(cpv->v.v, X509_NAME_free);
                break;
              default:
                break;
            }
        }
    }
}


static int
mod_openssl_load_verify_locn (SSL_CTX *ssl_ctx, const buffer *b, server *srv)
{
    const char *fn = b->ptr;
    if (1 == SSL_CTX_load_verify_locations(ssl_ctx, fn, NULL))
        return 1;

    log_error(srv->errh, __FILE__, __LINE__,
      "SSL: %s %s", ERR_error_string(ERR_get_error(), NULL), fn);
    return 0;
}


static int
mod_openssl_load_ca_files (SSL_CTX *ssl_ctx, plugin_data *p, server *srv)
{
    /* load all ssl.ca-files specified in the config
     * into each SSL_CTX to be prepared for SNI */

    for (uint32_t i = 0, used = p->cafiles->used; i < used; ++i) {
        const buffer *b = &((data_string *)p->cafiles->data[i])->value;
        if (!mod_openssl_load_verify_locn(ssl_ctx, b, srv))
            return 0;
    }
    return 1;
}


FREE_FUNC(mod_openssl_free)
{
    plugin_data *p = p_d;
    if (NULL == p->srv) return;
    mod_openssl_free_config(p->srv, p);
    mod_openssl_free_openssl();
}


static void
mod_openssl_merge_config_cpv (plugin_config * const pconf, const config_plugin_value_t * const cpv)
{
    switch (cpv->k_id) { /* index into static config_plugin_keys_t cpk[] */
      case 0: /* ssl.pemfile */
        if (cpv->vtype == T_CONFIG_LOCAL) {
            plugin_cert *pc = cpv->v.v;
            pconf->ssl_pemfile_pkey = pc->ssl_pemfile_pkey;
            pconf->ssl_pemfile_x509 = pc->ssl_pemfile_x509;
            pconf->ssl_pemfile      = pc->ssl_pemfile;
        }
        break;
      case 1: /* ssl.privkey */
        break;
      case 2: /* ssl.ca-file */
        if (cpv->vtype == T_CONFIG_LOCAL)
            pconf->ssl_ca_file = cpv->v.v;
        break;
      case 3: /* ssl.ca-dn-file */
        if (cpv->vtype == T_CONFIG_LOCAL)
            pconf->ssl_ca_dn_file = cpv->v.v;
        break;
      case 4: /* ssl.ca-crl-file */
        pconf->ssl_ca_crl_file = cpv->v.b;
        break;
      case 5: /* ssl.read-ahead */
        pconf->ssl_read_ahead = (0 != cpv->v.u);
        break;
      case 6: /* ssl.disable-client-renegotiation */
        pconf->ssl_disable_client_renegotiation = (0 != cpv->v.u);
        break;
      case 7: /* ssl.verifyclient.activate */
        pconf->ssl_verifyclient = (0 != cpv->v.u);
        break;
      case 8: /* ssl.verifyclient.enforce */
        pconf->ssl_verifyclient_enforce = (0 != cpv->v.u);
        break;
      case 9: /* ssl.verifyclient.depth */
        pconf->ssl_verifyclient_depth = (unsigned char)cpv->v.shrt;
        break;
      case 10:/* ssl.verifyclient.username */
        pconf->ssl_verifyclient_username = cpv->v.b;
        break;
      case 11:/* ssl.verifyclient.exportcert */
        pconf->ssl_verifyclient_export_cert = (0 != cpv->v.u);
        break;
      case 12:/* ssl.acme-tls-1 */
        pconf->ssl_acme_tls_1 = cpv->v.b;
        break;
      case 13:/* debug.log-ssl-noise */
        pconf->ssl_log_noise = (0 != cpv->v.u);
        break;
      default:/* should not happen */
        return;
    }
}


static void
mod_openssl_merge_config(plugin_config * const pconf, const config_plugin_value_t *cpv)
{
    do {
        mod_openssl_merge_config_cpv(pconf, cpv);
    } while ((++cpv)->k_id != -1);
}


static void
mod_openssl_patch_config (request_st * const r, plugin_config * const pconf)
{
    plugin_data * const p = plugin_data_singleton;
    memcpy(pconf, &p->defaults, sizeof(plugin_config));
    for (int i = 1, used = p->nconfig; i < used; ++i) {
        if (config_check_cond(r, (uint32_t)p->cvlist[i].k_id))
            mod_openssl_merge_config(pconf, p->cvlist + p->cvlist[i].v.u2[0]);
    }
}


static int
safer_X509_NAME_oneline(X509_NAME *name, char *buf, size_t sz)
{
    BIO *bio = BIO_new(BIO_s_mem());
    if (bio) {
        int len = X509_NAME_print_ex(bio, name, 0, XN_FLAG_ONELINE);
        BIO_gets(bio, buf, (int)sz); /*(may be truncated if len >= sz)*/
        BIO_free(bio);
        return len; /*return value has similar semantics to that of snprintf()*/
    }
    else {
        buf[0] = '\0';
        return -1;
    }
}


static void
ssl_info_callback (const SSL *ssl, int where, int ret)
{
    UNUSED(ret);

    if (0 != (where & SSL_CB_HANDSHAKE_START)) {
        handler_ctx *hctx = (handler_ctx *) SSL_get_app_data(ssl);
        if (hctx->renegotiations >= 0) ++hctx->renegotiations;
    }
  #ifdef TLS1_3_VERSION
    /* https://github.com/openssl/openssl/issues/5721
     * "TLSv1.3 unexpected InfoCallback after handshake completed" */
    if (0 != (where & SSL_CB_HANDSHAKE_DONE)) {
        /* SSL_version() is valid after initial handshake completed */
        if (SSL_version(ssl) >= TLS1_3_VERSION) {
            /* https://wiki.openssl.org/index.php/TLS1.3
             * "Renegotiation is not possible in a TLSv1.3 connection" */
            handler_ctx *hctx = (handler_ctx *) SSL_get_app_data(ssl);
            hctx->renegotiations = -1;
        }
    }
  #endif
}

/* https://wiki.openssl.org/index.php/Manual:SSL_CTX_set_verify(3)#EXAMPLES */
static int
verify_callback(int preverify_ok, X509_STORE_CTX *ctx)
{
    char buf[256];
    X509 *err_cert;
    int err, depth;
    SSL *ssl;
    handler_ctx *hctx;

    err = X509_STORE_CTX_get_error(ctx);
    depth = X509_STORE_CTX_get_error_depth(ctx);

    /*
     * Retrieve the pointer to the SSL of the connection currently treated
     * and the application specific data stored into the SSL object.
     */
    ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
    hctx = (handler_ctx *) SSL_get_app_data(ssl);

    /*
     * Catch a too long certificate chain. The depth limit set using
     * SSL_CTX_set_verify_depth() is by purpose set to "limit+1" so
     * that whenever the "depth>verify_depth" condition is met, we
     * have violated the limit and want to log this error condition.
     * We must do it here, because the CHAIN_TOO_LONG error would not
     * be found explicitly; only errors introduced by cutting off the
     * additional certificates would be logged.
     */
    if (depth > hctx->conf.ssl_verifyclient_depth) {
        preverify_ok = 0;
        err = X509_V_ERR_CERT_CHAIN_TOO_LONG;
        X509_STORE_CTX_set_error(ctx, err);
    }

    if (preverify_ok && 0 == depth
        && NULL != hctx->conf.ssl_ca_dn_file
        && NULL != hctx->conf.ssl_ca_file) {
        /* verify that client cert is issued by CA in ssl.ca-dn-file
         * if both ssl.ca-dn-file and ssl.ca-file were configured */
        STACK_OF(X509_NAME) * const cert_names = hctx->conf.ssl_ca_dn_file;
        X509_NAME *issuer;
      #if OPENSSL_VERSION_NUMBER >= 0x10002000L
        err_cert = X509_STORE_CTX_get_current_cert(ctx);
      #else
        err_cert = ctx->current_cert;
      #endif
        if (NULL == err_cert) return !hctx->conf.ssl_verifyclient_enforce;
        issuer = X509_get_issuer_name(err_cert);
      #if 0 /*(?desirable/undesirable to have cert_names sorted?)*/
        if (-1 != sk_X509_NAME_find(cert_names, issuer))
            return preverify_ok; /* match */
      #else
        for (int i = 0, len = sk_X509_NAME_num(cert_names); i < len; ++i) {
            if (0 == X509_NAME_cmp(sk_X509_NAME_value(cert_names, i), issuer))
                return preverify_ok; /* match */
        }
      #endif

        preverify_ok = 0;
        err = X509_V_ERR_CERT_REJECTED;
        X509_STORE_CTX_set_error(ctx, err);
    }

    if (preverify_ok) {
        return preverify_ok;
    }

  #if OPENSSL_VERSION_NUMBER >= 0x10002000L
    err_cert = X509_STORE_CTX_get_current_cert(ctx);
  #else
    err_cert = ctx->current_cert;
  #endif
    if (NULL == err_cert) return !hctx->conf.ssl_verifyclient_enforce;
    safer_X509_NAME_oneline(X509_get_subject_name(err_cert),buf,sizeof(buf));
    log_error_st *errh = hctx->r->conf.errh;
    log_error(errh, __FILE__, __LINE__,
      "SSL: verify error:num=%d:%s:depth=%d:subject=%s",
      err, X509_verify_cert_error_string(err), depth, buf);

    /*
     * At this point, err contains the last verification error. We can use
     * it for something special
     */
    if (!preverify_ok && (err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY ||
                          err == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT)) {
        safer_X509_NAME_oneline(X509_get_issuer_name(err_cert),buf,sizeof(buf));
        log_error(errh, __FILE__, __LINE__, "SSL: issuer=%s", buf);
    }

    return !hctx->conf.ssl_verifyclient_enforce;
}

#ifndef OPENSSL_NO_TLSEXT
static int
mod_openssl_SNI (SSL *ssl, handler_ctx *hctx, const char *servername, size_t len)
{
    request_st * const r = hctx->r;
    if (len >= 1024) { /*(expecting < 256; TLSEXT_MAXLEN_host_name is 255)*/
        log_error(r->conf.errh, __FILE__, __LINE__,
                  "SSL: SNI name too long %.*s", (int)len, servername);
        return SSL_TLSEXT_ERR_ALERT_FATAL;
    }

    /* use SNI to patch mod_openssl config and then reset COMP_HTTP_HOST */
    buffer_copy_string_len(&r->uri.authority, servername, len);
    buffer_to_lower(&r->uri.authority);
  #if 0
    /*(r->uri.authority used below for configuration before request read;
     * revisit for h2)*/
    if (0 != http_request_host_policy(&r->uri.authority,
                                      r->conf.http_parseopts, 443))
        return SSL_TLSEXT_ERR_ALERT_FATAL;
  #endif

    const buffer * const ssl_pemfile = hctx->conf.ssl_pemfile;

    r->conditional_is_valid |= (1 << COMP_HTTP_SCHEME)
                            |  (1 << COMP_HTTP_HOST);
    mod_openssl_patch_config(r, &hctx->conf);
    /* reset COMP_HTTP_HOST so that conditions re-run after request hdrs read */
    /*(done in response.c:config_cond_cache_reset() after request hdrs read)*/
    /*config_cond_cache_reset_item(r, COMP_HTTP_HOST);*/
    /*buffer_clear(&r->uri.authority);*/

    if (!buffer_is_equal(hctx->conf.ssl_pemfile, ssl_pemfile)) {
        /* reconfigure to use SNI-specific cert if SNI-specific cert provided */

        if (NULL == hctx->conf.ssl_pemfile_x509
            || NULL == hctx->conf.ssl_pemfile_pkey) {
            /* x509/pkey available <=> pemfile was set <=> pemfile got patched:
             * so this should never happen, unless you nest $SERVER["socket"] */
            log_error(r->conf.errh, __FILE__, __LINE__,
              "SSL: no certificate/private key for TLS server name %s",
              r->uri.authority.ptr);
            return SSL_TLSEXT_ERR_ALERT_FATAL;
        }

        /* first set certificate!
         * setting private key checks whether certificate matches it */
        if (1 != SSL_use_certificate(ssl, hctx->conf.ssl_pemfile_x509)) {
            log_error(r->conf.errh, __FILE__, __LINE__,
              "SSL: failed to set certificate for TLS server name %s: %s",
              r->uri.authority.ptr, ERR_error_string(ERR_get_error(), NULL));
            return SSL_TLSEXT_ERR_ALERT_FATAL;
        }

        if (1 != SSL_use_PrivateKey(ssl, hctx->conf.ssl_pemfile_pkey)) {
            log_error(r->conf.errh, __FILE__, __LINE__,
              "SSL: failed to set private key for TLS server name %s: %s",
              r->uri.authority.ptr, ERR_error_string(ERR_get_error(), NULL));
            return SSL_TLSEXT_ERR_ALERT_FATAL;
        }
    }

    if (hctx->conf.ssl_verifyclient) {
        int mode;
        STACK_OF(X509_NAME) * const cert_names = hctx->conf.ssl_ca_dn_file
          ? hctx->conf.ssl_ca_dn_file
          : hctx->conf.ssl_ca_file;
        if (NULL == cert_names) {
            log_error(r->conf.errh, __FILE__, __LINE__,
              "SSL: can't verify client without ssl.ca-file "
              "or ssl.ca-dn-file for TLS server name %s: %s",
              r->uri.authority.ptr, ERR_error_string(ERR_get_error(), NULL));
            return SSL_TLSEXT_ERR_ALERT_FATAL;
        }

        SSL_set_client_CA_list(ssl, SSL_dup_CA_list(cert_names));
        /* forcing verification here is really not that useful
         * -- a client could just connect without SNI */
        mode = SSL_VERIFY_PEER;
        if (hctx->conf.ssl_verifyclient_enforce) {
            mode |= SSL_VERIFY_FAIL_IF_NO_PEER_CERT;
        }
        SSL_set_verify(ssl, mode, verify_callback);
        SSL_set_verify_depth(ssl, hctx->conf.ssl_verifyclient_depth + 1);
    } else {
        SSL_set_verify(ssl, SSL_VERIFY_NONE, NULL);
    }

    return SSL_TLSEXT_ERR_OK;
}

#ifdef SSL_CLIENT_HELLO_SUCCESS
static int
mod_openssl_client_hello_cb (SSL *ssl, int *al, void *srv)
{
    handler_ctx *hctx = (handler_ctx *) SSL_get_app_data(ssl);
    buffer_copy_string(&hctx->r->uri.scheme, "https");
    UNUSED(srv);

    const unsigned char *name;
    size_t len, slen;
    if (!SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_server_name, &name, &len)) {
        return SSL_CLIENT_HELLO_SUCCESS; /* client did not provide SNI */
    }

    /* expecting single element in the server_name extension; parse first one */
    if (len > 5
        && (size_t)((name[0] << 8) + name[1]) == len-2
        && name[2] == TLSEXT_TYPE_server_name
        && (slen = (name[3] << 8) + name[4]) <= len-5) { /*(first)*/
        int rc = mod_openssl_SNI(ssl, hctx, (const char *)name+5, slen);
        if (rc == SSL_TLSEXT_ERR_OK)
            return SSL_CLIENT_HELLO_SUCCESS;
    }

    *al = TLS1_AD_UNRECOGNIZED_NAME;
    return SSL_CLIENT_HELLO_ERROR;
}
#else
static int
network_ssl_servername_callback (SSL *ssl, int *al, server *srv)
{
    handler_ctx *hctx = (handler_ctx *) SSL_get_app_data(ssl);
    buffer_copy_string(&hctx->r->uri.scheme, "https");
    UNUSED(al);
    UNUSED(srv);

    const char *servername = SSL_get_servername(ssl, TLSEXT_NAMETYPE_host_name);
    return (NULL != servername)
      ? mod_openssl_SNI(ssl, hctx, servername, strlen(servername))
      : SSL_TLSEXT_ERR_NOACK; /* client did not provide SNI */
}
#endif
#endif


static X509 *
x509_load_pem_file (const char *file, log_error_st *errh)
{
    BIO *in;
    X509 *x = NULL;

    in = BIO_new(BIO_s_file());
    if (NULL == in) {
        log_error(errh, __FILE__, __LINE__,
          "SSL: BIO_new(BIO_s_file()) failed");
        goto error;
    }

    if (BIO_read_filename(in,file) <= 0) {
        log_error(errh, __FILE__, __LINE__,
          "SSL: BIO_read_filename('%s') failed", file);
        goto error;
    }

    x = PEM_read_bio_X509(in, NULL, NULL, NULL);
    if (NULL == x) {
        log_error(errh, __FILE__, __LINE__,
          "SSL: couldn't read X509 certificate from '%s'", file);
        goto error;
    }

    BIO_free(in);
    return x;

error:
    if (NULL != in) BIO_free(in);
    return NULL;
}


static EVP_PKEY *
evp_pkey_load_pem_file (const char *file, log_error_st *errh)
{
    BIO *in;
    EVP_PKEY *x = NULL;

    in = BIO_new(BIO_s_file());
    if (NULL == in) {
        log_error(errh, __FILE__, __LINE__,
          "SSL: BIO_new(BIO_s_file()) failed");
        goto error;
    }

    if (BIO_read_filename(in,file) <= 0) {
        log_error(errh, __FILE__, __LINE__,
          "SSL: BIO_read_filename('%s') failed", file);
        goto error;
    }

    x = PEM_read_bio_PrivateKey(in, NULL, NULL, NULL);
    if (NULL == x) {
        log_error(errh, __FILE__, __LINE__,
          "SSL: couldn't read private key from '%s'", file);
        goto error;
    }

    BIO_free(in);
    return x;

error:
    if (NULL != in) BIO_free(in);
    return NULL;