lighttpd1.4/src/mod_gnutls.c

/*
 * mod_gnutls - GnuTLS support for lighttpd
 *
 * Copyright(c) 2020 Glenn Strauss gstrauss()gluelogic.com  All rights reserved
 * License: BSD 3-clause (same as lighttpd)
 */
/*
 * GnuTLS manual: https://www.gnutls.org/documentation.html
 *
 * future possible enhancements: OCSP stapling
 *
 * Note: session tickets are disabled by default.  If enabled,
 *   mod_gnutls 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 <sys/types.h>
#include <errno.h>
#include <stdarg.h>
#include <stdlib.h>
#include <stdio.h>      /* vsnprintf() */
#include <string.h>
#include <unistd.h>

#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#include <gnutls/abstract.h>

#ifdef GNUTLS_SKIP_GLOBAL_INIT
GNUTLS_SKIP_GLOBAL_INIT
#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 */
    gnutls_certificate_credentials_t ssl_cred;
    char trust_inited;
    gnutls_datum_t *ssl_pemfile_x509;
    gnutls_privkey_t ssl_pemfile_pkey;
} plugin_cert;

typedef struct {
    int8_t ssl_session_ticket;
    /*(preserved here for deinit at server shutdown)*/
    gnutls_priority_t priority_cache;
  #if GNUTLS_VERSION_NUMBER < 0x030600
    gnutls_dh_params_t dh_params;
  #endif
} plugin_ssl_ctx;

typedef struct {
    plugin_cert *pc;

    /*(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;
    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)*/
    gnutls_priority_t priority_cache;
    unsigned char ssl_session_ticket;
    unsigned char ssl_verifyclient;
    unsigned char ssl_verifyclient_enforce;
    unsigned char ssl_verifyclient_depth;

    const char *priority_base;
    buffer priority_str;
  #if GNUTLS_VERSION_NUMBER < 0x030600
    gnutls_dh_params_t dh_params;
  #endif
} plugin_config_socket; /*(used at startup during configuration)*/

typedef struct {
    /* SNI per host: w/ COMP_SERVER_SOCKET, COMP_HTTP_SCHEME, COMP_HTTP_HOST */
    plugin_cert *pc;
    gnutls_datum_t *ssl_ca_file;    /* .data is (gnutls_x509_crt_t) */
    gnutls_datum_t *ssl_ca_dn_file; /* .data is (gnutls_x509_crt_t) */
    gnutls_datum_t *ssl_ca_crl_file;/* .data is (gnutls_x509_crl_t) */

    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;
  #if GNUTLS_VERSION_NUMBER < 0x030600
    gnutls_dh_params_t dh_params;
  #endif
} plugin_config;

typedef struct {
    PLUGIN_DATA;
    plugin_ssl_ctx *ssl_ctxs;
    plugin_config defaults;
    server *srv;
} 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 16384 /* DEFAULT_MAX_RECORD_SIZE */
static char *local_send_buffer;

typedef struct {
    gnutls_session_t ssl;      /* gnutls request/connection context */
    request_st *r;
    connection *con;
    int8_t request_env_patched;
    int8_t close_notify;
    uint8_t alpn;
    int8_t ssl_session_ticket;
    int handshake;
    size_t pending_write;
    plugin_config conf;
    unsigned int verify_status;
    buffer *tmp_buf;
    gnutls_certificate_credentials_t acme_tls_1_cred;
} 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)
{
    gnutls_deinit(hctx->ssl);
    if (hctx->acme_tls_1_cred)
        gnutls_certificate_free_credentials(hctx->acme_tls_1_cred);
    free(hctx);
}


__attribute_cold__
static void elog(log_error_st * const errh,
                 const char * const file, const int line,
                 const int rc, const char * const msg)
{
    /* error logging convenience function that decodes gnutls result codes */
    log_error(errh, file, line, "GnuTLS: %s: (%s) %s",
              msg, gnutls_strerror_name(rc), gnutls_strerror(rc));
}


__attribute_cold__
__attribute_format__((__printf__, 5, 6))
static void elogf(log_error_st * const errh,
                  const char * const file, const int line,
                  const int rc, const char * const fmt, ...)
{
    char msg[1024];
    va_list ap;
    va_start(ap, fmt);
    vsnprintf(msg, sizeof(msg), fmt, ap);
    va_end(ap);
    elog(errh, file, line, rc, msg);
}


/* gnutls func gnutls_load_file() loads file contents into a gnutls_datum_t.
 * The data loaded could be sensitive, e.g. a private key included in a pemfile.
 * However, gnutls_load_file() is not careful about zeroizing memory on error,
 * might use realloc() (which does not guarantee to zeroize memory released),
 * and silently continues on short read, so provide our own.  Updates to
 * gnutls 3.6.14 may be more careful with private key files, but do not
 * extend the same care to pemfiles which might contain private keys.
 * Related, see also mod_gnutls_datum_wipe() below.
 *   https://gitlab.com/gnutls/gnutls/-/issues/1001
 *   https://gitlab.com/gnutls/gnutls/-/issues/1002
 *   https://gitlab.com/gnutls/gnutls/-/merge_requests/1270
 */
#include <sys/stat.h>
#include <fcntl.h>
#include <limits.h>
#include "fdevent.h"
static int
mod_gnutls_load_file (const char * const fn, gnutls_datum_t * const d, log_error_st *errh)
{
  #if 0
    int rc = gnutls_load_file(fn, d);
    if (rc < 0)
        elogf(errh, __FILE__, __LINE__, rc, "%s() %s", __func__, fn);
    return rc;
  #else
    int fd = -1;
    unsigned int sz = 0;
    char *buf = NULL;
    do {
        fd = fdevent_open_cloexec(fn, 1, O_RDONLY, 0); /*(1: follows symlinks)*/
        if (fd < 0) break;

        struct stat st;
        if (0 != fstat(fd, &st)) break;
        if (st.st_size >= UINT_MAX) { /*(file too large for gnutls_datum_t)*/
            errno = EOVERFLOW;
            break;
        }

        sz = (unsigned int)st.st_size;
        buf = gnutls_malloc(sz+1); /*(+1 trailing '\0' for gnutls_load_file())*/
        if (NULL == buf) break;

        ssize_t rd = 0;
        unsigned int off = 0;
        do {
            rd = read(fd, buf+off, sz-off);
        } while (rd > 0 ? (off += (unsigned int)rd) != sz : errno == EINTR);
        if (off != sz) { /*(file truncated?)*/
            if (rd >= 0) errno = EIO;
            break;
        }

        buf[sz] = '\0';
        d->data = (unsigned char *)buf;
        d->size = sz;
        close(fd);
        return 0;
    } while (0);
    int errnum = errno;
    log_perror(errh, __FILE__, __LINE__, "%s() %s", __func__, fn);
    if (fd >= 0) close(fd);
    if (buf) {
        gnutls_memset(buf, 0, sz);
        gnutls_free(buf);
    }
    errno = errnum;
    return GNUTLS_E_FILE_ERROR;
  #endif
}


/* GnuTLS does not expose _gnutls_free_key_datum() so provide our own */
static void
mod_gnutls_datum_wipe (gnutls_datum_t * const d)
{
    if (NULL == d) return;
    if (d->data) {
        if (d->size) gnutls_memset(d->data, 0, d->size);
        gnutls_free(d->data);
        d->data = NULL;
    }
    d->size = 0;
}


static time_t stek_rotate_ts;
static gnutls_datum_t session_ticket_key;
static void
mod_gnutls_session_ticket_key_free (void)
{
    mod_gnutls_datum_wipe(&session_ticket_key);
}
static void
mod_gnutls_session_ticket_key_init (server *srv)
{
    int rc = gnutls_session_ticket_key_generate(&session_ticket_key);
    if (rc < 0) {
        /*(should not happen, but if it does, disable session ticket)*/
        session_ticket_key.size = 0;
        elog(srv->errh, __FILE__, __LINE__, rc,
             "gnutls_session_ticket_key_generate()");
    }
}
static void
mod_gnutls_session_ticket_key_rotate (server *srv)
{
    mod_gnutls_session_ticket_key_free();
    mod_gnutls_session_ticket_key_init(srv);
}


INIT_FUNC(mod_gnutls_init)
{
    plugin_data_singleton = (plugin_data *)calloc(1, sizeof(plugin_data));
    return plugin_data_singleton;
}


static int mod_gnutls_init_once_gnutls (void)
{
    if (ssl_is_init) return 1;
    ssl_is_init = 1;

    /* Note: on systems with support for weak symbols, GNUTLS_SKIP_GLOBAL_INIT
     * is set near top of this file to inhibit GnuTLS implicit initialization
     * in a library constructor.  On systems without support for weak symbols,
     * set GNUTLS_NO_EXPLICIT_INIT=1 in the environment before starting lighttpd
     * (GnuTLS 3.3.0 or later) */

    if (gnutls_global_init() != GNUTLS_E_SUCCESS)
        return 0;

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

    return 1;
}


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

    mod_gnutls_session_ticket_key_free();

    gnutls_global_deinit();

    free(local_send_buffer);
    ssl_is_init = 0;
}


static void
mod_gnutls_free_config_crts (gnutls_datum_t *d)
{
    if (NULL == d) return;
    gnutls_x509_crt_t *crts = (gnutls_x509_crt_t *)(void *)d->data;
    unsigned int u = d->size;
    for (unsigned int i = 0; i < u; ++i)
        gnutls_x509_crt_deinit(crts[i]);
    gnutls_free(crts);
    gnutls_free(d);
}


static void
mod_gnutls_free_config_crls (gnutls_datum_t *d)
{
    if (NULL == d) return;
    gnutls_x509_crl_t *crls = (gnutls_x509_crl_t *)(void *)d->data;
    unsigned int u = d->size;
    for (unsigned int i = 0; i < u; ++i)
        gnutls_x509_crl_deinit(crls[i]);
    gnutls_free(crls);
    gnutls_free(d);
}


static gnutls_datum_t *
mod_gnutls_load_config_crts (const char *fn, log_error_st *errh)
{
    /*(very similar to other mod_gnutls_load_config_*())*/
    if (!mod_gnutls_init_once_gnutls()) return NULL;

    gnutls_datum_t f = { NULL, 0 };
    int rc = mod_gnutls_load_file(fn, &f, errh);
    if (rc < 0) return NULL;
    gnutls_datum_t *d = gnutls_malloc(sizeof(gnutls_datum_t));
    if (d == NULL) {
        mod_gnutls_datum_wipe(&f);
        return NULL;
    }
    d->data = NULL;
    d->size = 0;
    rc = gnutls_x509_crt_list_import2((gnutls_x509_crt_t **)&d->data, &d->size,
                                      &f, GNUTLS_X509_FMT_PEM,
                                      GNUTLS_X509_CRT_LIST_SORT);
    mod_gnutls_datum_wipe(&f);
    if (rc < 0) {
        elogf(errh, __FILE__, __LINE__, rc,
              "gnutls_x509_crt_list_import2() %s", fn);
        mod_gnutls_free_config_crts(d);
        return NULL;
    }

    return d;
}


static gnutls_datum_t *
mod_gnutls_load_config_crls (const char *fn, log_error_st *errh)
{
    /*(very similar to other mod_gnutls_load_config_*())*/
    if (!mod_gnutls_init_once_gnutls()) return NULL;

    gnutls_datum_t f = { NULL, 0 };
    int rc = mod_gnutls_load_file(fn, &f, errh);
    if (rc < 0) return NULL;
    gnutls_datum_t *d = gnutls_malloc(sizeof(gnutls_datum_t));
    if (d == NULL) {
        mod_gnutls_datum_wipe(&f);
        return NULL;
    }
    d->data = NULL;
    d->size = 0;
    rc = gnutls_x509_crl_list_import2((gnutls_x509_crl_t **)&d->data, &d->size,
                                      &f, GNUTLS_X509_FMT_PEM, 0);
    mod_gnutls_datum_wipe(&f);
    if (rc < 0) {
        elogf(errh, __FILE__, __LINE__, rc,
              "gnutls_x509_crl_list_import2() %s", fn);
        mod_gnutls_free_config_crls(d);
        return NULL;
    }

    return d;
}


static gnutls_privkey_t
mod_gnutls_load_config_pkey (const char *fn, log_error_st *errh)
{
    /*(very similar to other mod_gnutls_load_config_*())*/
    if (!mod_gnutls_init_once_gnutls()) return NULL;

    gnutls_datum_t f = { NULL, 0 };
    int rc = mod_gnutls_load_file(fn, &f, errh);
    if (rc < 0) return NULL;
    gnutls_privkey_t pkey;
    rc = gnutls_privkey_init(&pkey);
    if (rc < 0) {
        mod_gnutls_datum_wipe(&f);
        return NULL;
    }
    rc = gnutls_privkey_import_x509_raw(pkey, &f, GNUTLS_X509_FMT_PEM, NULL, 0);
    mod_gnutls_datum_wipe(&f);
    if (rc < 0) {
        elogf(errh, __FILE__, __LINE__, rc,
              "gnutls_privkey_import_x509_raw() %s", fn);
        gnutls_privkey_deinit(pkey);
        return NULL;
    }

    return pkey;
}


static void
mod_gnutls_free_config (server *srv, plugin_data * const p)
{
    if (NULL != p->ssl_ctxs) {
        gnutls_priority_t pcache_global_scope = p->ssl_ctxs->priority_cache;
        /* free 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->priority_cache && s->priority_cache != pcache_global_scope) {
                if (s->priority_cache)
                    gnutls_priority_deinit(s->priority_cache);
              #if GNUTLS_VERSION_NUMBER < 0x030600
                if (s->dh_params)
                    gnutls_dh_params_deinit(s->dh_params);
              #endif
            }
        }
        /* free from global scope */
        if (pcache_global_scope) {
            if (p->ssl_ctxs[0].priority_cache)
                gnutls_priority_deinit(p->ssl_ctxs[0].priority_cache);
          #if GNUTLS_VERSION_NUMBER < 0x030600
            if (p->ssl_ctxs[0].dh_params)
                gnutls_dh_params_deinit(p->ssl_ctxs[0].dh_params);
          #endif
        }
        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;
                    gnutls_certificate_free_credentials(pc->ssl_cred);
                    mod_gnutls_free_config_crts(pc->ssl_pemfile_x509);
                    gnutls_privkey_deinit(pc->ssl_pemfile_pkey);
                    free(pc);
                }
                break;
              case 2: /* ssl.ca-file */
              case 3: /* ssl.ca-dn-file */
                if (cpv->vtype == T_CONFIG_LOCAL)
                    mod_gnutls_free_config_crts(cpv->v.v);
                break;
              case 4: /* ssl.ca-crl-file */
                if (cpv->vtype == T_CONFIG_LOCAL)
                    mod_gnutls_free_config_crls(cpv->v.v);
                break;
              default:
                break;
            }
        }
    }
}


FREE_FUNC(mod_gnutls_free)
{
    plugin_data *p = p_d;
    if (NULL == p->srv) return;
    mod_gnutls_free_config(p->srv, p);
    mod_gnutls_free_gnutls();
}


static void
mod_gnutls_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)
            pconf->pc = cpv->v.v;
        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 */
        if (cpv->vtype == T_CONFIG_LOCAL)
            pconf->ssl_ca_crl_file = cpv->v.v;
        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 = (unsigned char)cpv->v.shrt;
        break;
      default:/* should not happen */
        return;
    }
}


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


static void
mod_gnutls_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_gnutls_merge_config(pconf, p->cvlist + p->cvlist[i].v.u2[0]);
    }
}


static int
mod_gnutls_verify_set_tlist (handler_ctx *hctx, int req)
{
    /* XXX GnuTLS interfaces appear to be better for client-side use than for
     * server-side use.  If gnutls_x509_trust_list_t were available to attach
     * to a gnutls_session_t (without copying), then there would not be race
     * conditions swapping trust lists on the credential *shared* between
     * connections when ssl.ca-dn-file and ssl.ca-file are both set.  If both
     * are set, current code attempts to set ssl.ca-dn-file right before sending
     * client cert request, and sets ssl.ca-file right before client cert verify
     *
     * Architecture would be cleaner if the trust list for verifying client cert
     * (gnutls_x509_trust_list_t) were available to attach to a gnutls_session_t
     * instead of attaching to a gnutls_certificate_credentials_t.
     */
    if (hctx->conf.pc->trust_inited) return GNUTLS_E_SUCCESS;

    gnutls_datum_t *d;
    int rc;

    /* set trust list using ssl_ca_dn_file, if set, for client cert request
     * (when req is true) (for CAs sent by server to client in cert request)
     * (trust is later replaced by ssl_ca_file for client cert verification) */
    d = req && hctx->conf.ssl_ca_dn_file
      ? hctx->conf.ssl_ca_dn_file
      : hctx->conf.ssl_ca_file;
    if (NULL == d) {
        log_error(hctx->r->conf.errh, __FILE__, __LINE__,
          "GnuTLS: can't verify client without ssl.ca-file "
          "for TLS server name %s",
          hctx->r->uri.authority.ptr); /*(might not be set yet if no SNI)*/
        return GNUTLS_E_INTERNAL_ERROR;
    }

    gnutls_x509_trust_list_t tlist = NULL;
    rc = gnutls_x509_trust_list_init(&tlist, 0);
    if (rc < 0) {
        elog(hctx->r->conf.errh, __FILE__, __LINE__, rc,
             "gnutls_x509_trust_list_init()");
        return rc;
    }

    gnutls_x509_crt_t *clist = (gnutls_x509_crt_t *)(void *)d->data;
    rc = gnutls_x509_trust_list_add_cas(tlist, clist, d->size, 0);
    if (rc < 0) {
        elog(hctx->r->conf.errh, __FILE__, __LINE__, rc,
             "gnutls_x509_trust_list_add_cas()");
        gnutls_x509_trust_list_deinit(tlist, 0);
        return rc;
    }

    d = hctx->conf.ssl_ca_crl_file;
    if (NULL != d && req && hctx->conf.ssl_ca_dn_file) {
        /*(check req and ssl_ca_dn_file to see if tlist will be replaced later,
         * and, if so, defer setting crls until later)*/
        gnutls_x509_crl_t *crl_list = (gnutls_x509_crl_t *)(void *)d->data;
        rc = gnutls_x509_trust_list_add_crls(tlist, crl_list, d->size, 0, 0);
        if (rc < 0) {
            elog(hctx->r->conf.errh, __FILE__, __LINE__, rc,
                 "gnutls_x509_trust_list_add_crls()");
            gnutls_x509_trust_list_deinit(tlist, 0);
            return rc;
        }
    }

    /* gnutls limitation; wasteful to have to copy into each cred */
    /* (would be better to share list with session, instead of with cred) */
    gnutls_certificate_credentials_t ssl_cred = hctx->conf.pc->ssl_cred;
    gnutls_certificate_set_trust_list(ssl_cred, tlist, 0); /* transfer tlist */

    /* (must flip trust lists back and forth b/w DN names and verify CAs) */
    if (NULL == hctx->conf.ssl_ca_dn_file)
        hctx->conf.pc->trust_inited = 1;

    return GNUTLS_E_SUCCESS;
}


static int
mod_gnutls_verify_cb (gnutls_session_t ssl)
{
    handler_ctx * const hctx = gnutls_session_get_ptr(ssl);
    if (!hctx->conf.ssl_verifyclient) return 0;

    if (gnutls_auth_client_get_type(ssl) != GNUTLS_CRD_CERTIFICATE)
        return GNUTLS_E_SUCCESS;

    int rc;

    /* gnutls limitation; wasteful to have to copy into each cred */
    /* (would be better to share list with session, instead of with cred) */
    if (hctx->conf.ssl_ca_dn_file) {
        rc = mod_gnutls_verify_set_tlist(hctx, 0); /* for client cert verify */
        if (rc < 0) return rc;
    }

    /* gnutls_certificate_verify_peers2() includes processing OCSP staping,
     * as well as certificate depth verification before getting internal
     * flags and calling gnutls_x509_trust_list_verify_crt2()
     * advanced reference:
     *   gnutls lib/cert-sessions.c:_gnutls_x509_cert_verify_peers()
     * XXX: if GnuTLS provided a more advanced interface which permitted
     * providing trust list, verify depth, and flags, we could avoid copying
     * ca chain and crls into each credential, using
     *   gnutls_x509_trust_list_add_cas()
     *   gnutls_x509_trust_list_add_crls()
     *   gnutls_x509_trust_list_verify_crt2()
     * See also GnuTLS manual Section 7.3.4 Advanced certificate verification
     */

    rc = gnutls_certificate_verify_peers2(ssl, &hctx->verify_status);
    if (rc < 0) return rc;

    if (hctx->verify_status == 0 && hctx->conf.ssl_ca_dn_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 */
        gnutls_x509_crt_t *CA_list =
          (gnutls_x509_crt_t *)&hctx->conf.ssl_ca_dn_file->data;
        unsigned int len = hctx->conf.ssl_ca_dn_file->size;
        unsigned int i;
        gnutls_x509_dn_t issuer, subject;
        unsigned int crt_size = 0;
        const gnutls_datum_t *crts;
        gnutls_x509_crt_t crt = NULL;
        crts = gnutls_certificate_get_peers(ssl, &crt_size);
        if (0 == crt_size
            || gnutls_x509_crt_init(&crt) < 0
            || gnutls_x509_crt_import(crt, &crts[0], GNUTLS_X509_FMT_DER) < 0
            || gnutls_x509_crt_get_subject(crt, &issuer) < 0)
            len = 0; /*(trigger failure path below)*/
        for (i = 0; i < len; ++i) {
            if (gnutls_x509_crt_get_subject(CA_list[i], &subject) >= 0
                && 0 == memcmp(&subject, &issuer, sizeof(issuer)))
                break;
        }
        if (i == len)
            hctx->verify_status |= GNUTLS_CERT_SIGNER_NOT_CA;
        if (crt) gnutls_x509_crt_deinit(crt);
    }

    if (hctx->verify_status != 0 && hctx->conf.ssl_verifyclient_enforce) {
        /* (not looping on GNUTLS_E_INTERRUPTED or GNUTLS_E_AGAIN
         *  since we do not want to block here (and not expecting to have to))*/
        (void)gnutls_alert_send(ssl, GNUTLS_AL_FATAL, GNUTLS_A_ACCESS_DENIED);
        return GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR;
    }

    return GNUTLS_E_SUCCESS;
}


static int
mod_gnutls_construct_crt_chain (plugin_cert *pc, gnutls_datum_t *d, log_error_st *errh)
{
    /* Historically, openssl will use the cert chain in (SSL_CTX *) if a cert
     * does not have a chain configured in (SSL *).  Attempt to provide
     * compatible behavior here.  This may be called after startup since
     * ssl.pemfile might be defined in a config scope without ssl.ca-file,
     * and at runtime is when ssl.ca-file (e.g. from matching $SERVER["socket"])
     * would be known along with ssl.pemfile (e.g. from $HTTP["host"]) */

    gnutls_certificate_credentials_t ssl_cred;
    int rc = gnutls_certificate_allocate_credentials(&ssl_cred);
    if (rc < 0) return rc;
    unsigned int ncrt = (d ? d->size : 0);
    unsigned int off = (d == pc->ssl_pemfile_x509) ? 0 : 1;
    gnutls_pcert_st * const pcert_list =
      gnutls_malloc(sizeof(gnutls_pcert_st) * (off+ncrt));
    if (NULL == pcert_list) {
        gnutls_certificate_free_credentials(ssl_cred);
        return GNUTLS_E_MEMORY_ERROR;
    }
    memset(pcert_list, 0, sizeof(gnutls_pcert_st) * (off+ncrt));
    rc = 0;

    if (off) { /*(add crt to chain if different from d)*/
        /*assert(pc->ssl_pemfile_x509->size == 1)*/
        gnutls_x509_crt_t *crts =
          (gnutls_x509_crt_t *)(void *)pc->ssl_pemfile_x509->data;
        rc = gnutls_pcert_import_x509(pcert_list, crts[0], 0);
    }

    if (0 == rc && ncrt) {
        gnutls_x509_crt_t *crts = (gnutls_x509_crt_t *)(void *)d->data;
      #if GNUTLS_VERSION_NUMBER < 0x030400
        /*(GNUTLS_X509_CRT_LIST_SORT not needed; crts sorted when file read)*/
        rc = gnutls_pcert_import_x509_list(pcert_list+off, crts, &ncrt, 0);
      #else /* manually import list, but note that sorting is not implemented */
        rc = 0;
        for (unsigned int i = 0; i < ncrt; ++i) {
            rc = gnutls_pcert_import_x509(pcert_list+off+i, crts[i], 0);
            if (rc < 0) break;
        }
      #endif
    }
    ncrt += off;
    if (0 == rc)
        rc = gnutls_certificate_set_key(ssl_cred, NULL, 0, pcert_list, ncrt,
                                        pc->ssl_pemfile_pkey);
    if (rc < 0) {
        for (unsigned int i = 0; i < ncrt; ++i)
            gnutls_pcert_deinit(pcert_list+i);
        gnutls_free(pcert_list);
        gnutls_certificate_free_credentials(ssl_cred);
        elog(errh, __FILE__, __LINE__, rc, "gnutls_certificate_set_key()");
        return rc;
    }
    /* XXX: gnutls_certificate_set_key() has an inconsistent implementation.
     * On success, key ownership is transferred, and so should not be freed,
     * but pcert_list is a shallow memcpy(), so gnutls_pcert_deinit() should
     * not be run on gnutls_pcert_st in list, though top-level list storage
     * should be freed.  On failure, ownership is not transferred for either. */
    gnutls_free(pcert_list);
    pc->ssl_pemfile_pkey = NULL;
    pc->ssl_cred = ssl_cred;

    /* release lists used to configure pc->ssl_cred */
    mod_gnutls_free_config_crts(pc->ssl_pemfile_x509);
    pc->ssl_pemfile_x509 = NULL;

    return 0;
}


static void *
network_gnutls_load_pemfile (server *srv, const buffer *pemfile, const buffer *privkey)
{
  #if 0 /* see comments in mod_gnutls_construct_crt_chain() above */

    gnutls_certificate_credentials_t ssl_cred = NULL;
    int rc;

    rc = gnutls_certificate_allocate_credentials(&ssl_cred);
    if (rc < 0) return NULL;

    rc = gnutls_certificate_set_x509_key_file2(ssl_cred,
                                               pemfile->ptr, privkey->ptr,
                                               GNUTLS_X509_FMT_PEM, NULL, 0);
    if (rc < 0) {
        elogf(srv->errh, __FILE__, __LINE__, rc,
              "gnutls_certificate_set_x509_key_file2(%s, %s)",
              pemfile->ptr, privkey->ptr);
        gnutls_certificate_free_credentials(ssl_cred);
        return NULL;
    }

    plugin_cert *pc = malloc(sizeof(plugin_cert));
    force_assert(pc);
    pc->ssl_cred = ssl_cred;
    pc->trust_inited = 0;

    return pc;

  #else

    gnutls_datum_t *d = mod_gnutls_load_config_crts(pemfile->ptr, srv->errh);
    if (NULL == d) return NULL;
    if (0 == d->size) {
        mod_gnutls_free_config_crts(d);
        return NULL;
    }

    gnutls_privkey_t pkey = mod_gnutls_load_config_pkey(privkey->ptr,srv->errh);
    if (NULL == pkey) {
        mod_gnutls_free_config_crts(d);
        return NULL;
    }

    plugin_cert *pc = malloc(sizeof(plugin_cert));
    force_assert(pc);
    pc->ssl_cred = NULL;
    pc->trust_inited = 0;
    pc->ssl_pemfile_x509 = d;
    pc->ssl_pemfile_pkey = pkey;

    if (d->size > 1) { /*(certificate chain provided)*/
        int rc = mod_gnutls_construct_crt_chain(pc, d, srv->errh);
        if (rc < 0) {
            mod_gnutls_free_config_crts(d);
            gnutls_privkey_deinit(pkey);
            free(pc);
            return NULL;
        }
    }

    return pc;

  #endif
}


#if GNUTLS_VERSION_NUMBER >= 0x030200

static int
mod_gnutls_acme_tls_1 (handler_ctx *hctx)
{
    buffer * const b = hctx->tmp_buf;
    const buffer * const name = &hctx->r->uri.authority;
    log_error_st * const errh = hctx->r->conf.errh;
    int rc = GNUTLS_E_INVALID_REQUEST;

    /* check if acme-tls/1 protocol is enabled (path to dir of cert(s) is set)*/
    if (buffer_string_is_empty(hctx->conf.ssl_acme_tls_1))
        return 0; /*(should not happen)*/
    buffer_copy_buffer(b, hctx->conf.ssl_acme_tls_1);
    buffer_append_slash(b);

    /* check if SNI set server name (required for acme-tls/1 protocol)
     * and perform simple path checks for no '/'
     * and no leading '.' (e.g. ignore "." or ".." or anything beginning '.') */
    if (buffer_string_is_empty(name))   return rc;
    if (NULL != strchr(name->ptr, '/')) return rc;
    if (name->ptr[0] == '.')            return rc;
  #if 0
    if (0 != http_request_host_policy(name, hctx->r->conf.http_parseopts, 443))
        return rc;
  #endif
    buffer_append_string_buffer(b, name);

  #if 0

    buffer *privkey = buffer_init_buffer(b);
    buffer_append_string_len(b, CONST_STR_LEN(".crt.pem"));
    buffer_append_string_len(privkey, CONST_STR_LEN(".key.pem"));

    /*(similar to network_gnutls_load_pemfile() but propagates rc)*/
    gnutls_certificate_credentials_t ssl_cred = NULL;
    rc = gnutls_certificate_allocate_credentials(&ssl_cred);
    if (rc < 0) { buffer_free(privkey); return rc; }
    rc = gnutls_certificate_set_x509_key_file2(ssl_cred,
                                               b->ptr, privkey->ptr,
                                               GNUTLS_X509_FMT_PEM, NULL, 0);
    if (rc < 0) {
        elogf(errh, __FILE__, __LINE__, rc,
              "failed to load acme-tls/1 cert (%s, %s)",
              b->ptr, privkey->ptr);
        buffer_free(privkey);
        gnutls_certificate_free_credentials(ssl_cred);
        return rc;
    }
    buffer_free(privkey);

  #else

    /* gnutls_certificate_set_x509_key_file2() does not securely wipe
     * sensitive data from memory, so take a few extra steps */

    /* similar to network_gnutls_load_pemfile() */

    uint32_t len = buffer_string_length(b);
    buffer_append_string_len(b, CONST_STR_LEN(".crt.pem"));

    gnutls_datum_t *d = mod_gnutls_load_config_crts(b->ptr, errh);
    if (NULL == d) return GNUTLS_E_FILE_ERROR;
    if (0 == d->size) {
        mod_gnutls_free_config_crts(d);
        return GNUTLS_E_FILE_ERROR;
    }

    buffer_string_set_length(b, len);
    buffer_append_string_len(b, CONST_STR_LEN(".key.pem"));

    gnutls_privkey_t pkey = mod_gnutls_load_config_pkey(b->ptr, errh);
    if (NULL == pkey) {
        mod_gnutls_free_config_crts(d);
        return GNUTLS_E_FILE_ERROR;
    }

    plugin_cert pc;
    pc.ssl_cred = NULL;
    pc.trust_inited = 0;
    pc.ssl_pemfile_x509 = d;
    pc.ssl_pemfile_pkey = pkey;

    rc = mod_gnutls_construct_crt_chain(&pc, d, errh);
    if (rc < 0) {
        mod_gnutls_free_config_crts(d);
        gnutls_privkey_deinit(pkey);
        return rc;
    }

    gnutls_certificate_credentials_t ssl_cred = pc.ssl_cred;

  #endif

    hctx->acme_tls_1_cred = ssl_cred; /*(save ptr and free later)*/

    rc = gnutls_credentials_set(hctx->ssl, GNUTLS_CRD_CERTIFICATE, ssl_cred);
    if (rc < 0) {
        elogf(hctx->r->conf.errh, __FILE__, __LINE__, rc,
              "failed to set acme-tls/1 certificate for TLS server name %s",
              hctx->r->uri.authority.ptr);
        return rc;
    }

    return GNUTLS_E_SUCCESS; /* 0 */
}


enum {
  MOD_GNUTLS_ALPN_HTTP11      = 1
 ,MOD_GNUTLS_ALPN_HTTP10      = 2
 ,MOD_GNUTLS_ALPN_H2          = 3
 ,MOD_GNUTLS_ALPN_ACME_TLS_1  = 4
};


static int
mod_gnutls_alpn_select_cb (gnutls_session_t ssl, handler_ctx *hctx)
{
    const int i = 0;
    uint8_t proto;

    gnutls_datum_t d = { NULL, 0 };
    if (gnutls_alpn_get_selected_protocol(ssl, &d) < 0)
        return 0; /* ignore GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE */
    const char *in = (const char *)d.data;
    const int n = (int)d.size;

    switch (n) {
     #if 0
      case 2:  /* "h2" */
        if (in[i] == 'h' && in[i+1] == '2') {
            proto = MOD_GNUTLS_ALPN_H2;
            break;
        }
        return 0;
     #endif
      case 8:  /* "http/1.1" "http/1.0" */
        if (0 == memcmp(in+i, "http/1.", 7)) {
            if (in[i+7] == '1') {
                proto = MOD_GNUTLS_ALPN_HTTP11;
                break;
            }
            if (in[i+7] == '0') {
                proto = MOD_GNUTLS_ALPN_HTTP10;
                break;
            }
        }
        return 0;
      case 10: /* "acme-tls/1" */
        if (0 == memcmp(in+i, "acme-tls/1", 10)) {
            int rc = mod_gnutls_acme_tls_1(hctx);
            if (0 == rc) {
                proto = MOD_GNUTLS_ALPN_ACME_TLS_1;
                break;
            }
            return rc;
        }
        return 0;
      default:
        return 0;
    }

    hctx->alpn = proto;
    return 0;
}

#endif /* GNUTLS_VERSION_NUMBER >= 0x030200 */


static int
mod_gnutls_SNI(void *ctx, unsigned int tls_id,
               const unsigned char *servername, unsigned int len)
{
    if (tls_id != 0) return 0;

    /* server name */

    /* https://www.gnutls.org/manual/gnutls.html#Virtual-hosts-and-credentials
     * figure the advertized name - the following hack relies on the fact that
     * this extension only supports DNS names, and due to a protocol bug cannot
     * be extended to support anything else. */
    if (len < 5) return 0;
    len -= 5;
    servername += 5;
    handler_ctx * const hctx = (handler_ctx *) ctx;
    request_st * const r = hctx->r;
    buffer_copy_string(&r->uri.scheme, "https");

    if (len >= 1024) { /*(expecting < 256; TLSEXT_MAXLEN_host_name is 255)*/
        log_error(r->conf.errh, __FILE__, __LINE__,
                  "GnuTLS: SNI name too long %.*s", (int)len, servername);
        return GNUTLS_E_INVALID_REQUEST;
    }

    /* use SNI to patch mod_gnutls config and then reset COMP_HTTP_HOST */
    buffer_copy_string_len(&r->uri.authority, (const char *)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 GNUTLS_E_INVALID_REQUEST;
  #endif

    r->conditional_is_valid |= (1 << COMP_HTTP_SCHEME)
                            |  (1 << COMP_HTTP_HOST);

    mod_gnutls_patch_config(r, &hctx->conf);
    /* reset COMP_HTTP_HOST so that conditions re-run after request hdrs read */
    /*(done in configfile-glue.c:config_cond_cache_reset() after request hdrs read)*/
    /*config_cond_cache_reset_item(r, COMP_HTTP_HOST);*/
    /*buffer_clear(&r->uri.authority);*/

    return 0;
}


static int
mod_gnutls_client_hello_hook_post(gnutls_session_t ssl)
{
  #if GNUTLS_VERSION_NUMBER >= 0x030200
    handler_ctx * const hctx = gnutls_session_get_ptr(ssl);
    int rc = mod_gnutls_alpn_select_cb(ssl, hctx);
    if (rc < 0)
        return rc;

    /* check if acme-tls/1 protocol is enabled (path to dir of cert(s) is set)*/
    if (hctx->alpn == MOD_GNUTLS_ALPN_ACME_TLS_1) {
        /*(acme-tls/1 is separate from certificate auth access to website)*/
        gnutls_certificate_server_set_request(ssl, GNUTLS_CERT_IGNORE);
        return GNUTLS_E_SUCCESS; /* 0 */ /*(skip further session config below)*/
    }
  #endif

    return GNUTLS_E_SUCCESS; /* 0 */
}


static int
mod_gnutls_client_hello_hook(gnutls_session_t ssl, unsigned int htype,
                             unsigned when, unsigned int incoming,