]> arthur.barton.de Git - ngircd-alex.git/blobdiff - src/ngircd/conn-ssl.c
ngIRCd Release 27
[ngircd-alex.git] / src / ngircd / conn-ssl.c
index ba47e513603b69aba08f2b7cf25f6c20a1ad4555..abcf53c2f7dc811b8a6b5200505109e883fa75ed 100644 (file)
@@ -43,11 +43,15 @@ extern struct SSLOptions Conf_SSLOptions;
 #include <openssl/err.h>
 #include <openssl/rand.h>
 #include <openssl/dh.h>
+#include <openssl/x509v3.h>
+
+#define MAX_CERT_CHAIN_LENGTH  10      /* XXX: do not hardcode */
 
 static SSL_CTX * ssl_ctx;
 static DH *dh_params;
 
 static bool ConnSSL_LoadServerKey_openssl PARAMS(( SSL_CTX *c ));
+static bool ConnSSL_SetVerifyProperties_openssl PARAMS((SSL_CTX * c));
 #endif
 
 #ifdef HAVE_LIBGNUTLS
@@ -62,10 +66,19 @@ static bool ConnSSL_LoadServerKey_openssl PARAMS(( SSL_CTX *c ));
 
 #define MAX_HASH_SIZE  64      /* from gnutls-int.h */
 
-static gnutls_certificate_credentials_t x509_cred;
+typedef struct {
+       int refcnt;
+       gnutls_certificate_credentials_t x509_cred;
+       gnutls_dh_params_t dh_params;
+} x509_cred_slot;
+
+static array x509_creds = INIT_ARRAY;
+static size_t x509_cred_idx;
+
 static gnutls_dh_params_t dh_params;
-static gnutls_priority_t priorities_cache;
+static gnutls_priority_t priorities_cache = NULL;
 static bool ConnSSL_LoadServerKey_gnutls PARAMS(( void ));
+static bool ConnSSL_SetVerifyProperties_gnutls PARAMS((void));
 #endif
 
 #define SHA256_STRING_LEN      (32 * 2 + 1)
@@ -123,9 +136,37 @@ out:
 /**
  * Log OpenSSL error message.
  *
+ * @param level The log level
  * @param msg The error message.
  * @param info Additional information text or NULL.
  */
+static void
+LogOpenSSL_CertInfo(int level, X509 * cert, const char *msg)
+{
+       BIO *mem;
+       char *memptr;
+       long len;
+
+       assert(cert);
+       assert(msg);
+
+       if (!cert)
+               return;
+       mem = BIO_new(BIO_s_mem());
+       if (!mem)
+               return;
+       X509_NAME_print_ex(mem, X509_get_subject_name(cert), 0,
+                          XN_FLAG_ONELINE);
+       X509_NAME_print_ex(mem, X509_get_issuer_name(cert), 2, XN_FLAG_ONELINE);
+       if (BIO_write(mem, "", 1) == 1) {
+               len = BIO_get_mem_data(mem, &memptr);
+               if (memptr && len > 0)
+                       Log(level, "%s: \"%s\".", msg, memptr);
+       }
+       (void)BIO_set_close(mem, BIO_CLOSE);
+       BIO_free(mem);
+}
+
 static void
 LogOpenSSLError(const char *error, const char *info)
 {
@@ -168,8 +209,24 @@ pem_passwd_cb(char *buf, int size, int rwflag, void *password)
 
 
 static int
-Verify_openssl(UNUSED int preverify_ok, UNUSED X509_STORE_CTX *x509_ctx)
+Verify_openssl(int preverify_ok, X509_STORE_CTX * ctx)
 {
+#ifdef DEBUG
+       if (!preverify_ok) {
+               int err = X509_STORE_CTX_get_error(ctx);
+               LogDebug("Certificate validation failed: %s",
+                        X509_verify_cert_error_string(err));
+       }
+#else
+       (void)preverify_ok;
+       (void)ctx;
+#endif
+
+       /* Always(!) return success as we have to deal with invalid
+        * (self-signed, expired, ...) client certificates and with invalid
+        * server certificates when "SSLVerify" is disabled, which we don't
+        * know at this stage. Therefore we postpone this check, it will be
+        * (and has to be!) handled in cb_connserver_login_ssl(). */
        return 1;
 }
 #endif
@@ -266,6 +323,21 @@ void ConnSSL_Free(CONNECTION *c)
                gnutls_bye(sess, GNUTLS_SHUT_RDWR);
                gnutls_deinit(sess);
        }
+       x509_cred_slot *slot = array_get(&x509_creds, sizeof(x509_cred_slot), c->ssl_state.x509_cred_idx);
+       assert(slot != NULL);
+       assert(slot->refcnt > 0);
+       assert(slot->x509_cred != NULL);
+       slot->refcnt--;
+       if ((c->ssl_state.x509_cred_idx != x509_cred_idx) && (slot->refcnt <= 0)) {
+               LogDebug("Discarding X509 certificate credentials from slot %zd.",
+                        c->ssl_state.x509_cred_idx);
+               gnutls_certificate_free_keys(slot->x509_cred);
+               gnutls_certificate_free_credentials(slot->x509_cred);
+               slot->x509_cred = NULL;
+               gnutls_dh_params_deinit(slot->dh_params);
+               slot->dh_params = NULL;
+               slot->refcnt = 0;
+       }
 #endif
        assert(Conn_OPTION_ISSET(c, CONN_SSL));
        /* can't just set bitmask to 0 -- there are other, non-ssl related flags, e.g. CONN_ZIP. */
@@ -311,8 +383,18 @@ ConnSSL_InitLibrary( void )
                return false;
        }
 
-       if (!ConnSSL_LoadServerKey_openssl(newctx))
+       if (!ConnSSL_LoadServerKey_openssl(newctx)) {
+               /* Failed to read new key but an old ssl context
+                * already exists -> reuse old context */
+               if (ssl_ctx) {
+                       SSL_CTX_free(newctx);
+                       Log(LOG_WARNING,
+                       "Re-Initializing of SSL failed, using old keys!");
+                       return true;
+               }
+               /* No preexisting old context -> error. */
                goto out;
+       }
 
        if (SSL_CTX_set_cipher_list(newctx, Conf_SSLOptions.CipherList) == 0) {
                Log(LOG_ERR, "Failed to apply OpenSSL cipher list \"%s\"!",
@@ -321,10 +403,13 @@ ConnSSL_InitLibrary( void )
        }
 
        SSL_CTX_set_session_id_context(newctx, (unsigned char *)"ngircd", 6);
-       SSL_CTX_set_options(newctx, SSL_OP_SINGLE_DH_USE|SSL_OP_NO_SSLv2);
+       if (!ConnSSL_SetVerifyProperties_openssl(newctx))
+               goto out;
+       SSL_CTX_set_options(newctx,
+                           SSL_OP_SINGLE_DH_USE | SSL_OP_NO_SSLv2 |
+                           SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1 | SSL_OP_NO_TLSv1_1 |
+                           SSL_OP_NO_COMPRESSION);
        SSL_CTX_set_mode(newctx, SSL_MODE_ENABLE_PARTIAL_WRITE);
-       SSL_CTX_set_verify(newctx, SSL_VERIFY_PEER|SSL_VERIFY_CLIENT_ONCE,
-                          Verify_openssl);
        SSL_CTX_free(ssl_ctx);
        ssl_ctx = newctx;
        Log(LOG_INFO, "%s initialized.", OpenSSL_version(OPENSSL_VERSION));
@@ -338,22 +423,21 @@ out:
        int err;
        static bool initialized;
 
-       if (initialized) {
-               /* TODO: cannot reload gnutls keys: can't simply free x509
-                * context -- it may still be in use */
-               return false;
-       }
-
-       err = gnutls_global_init();
-       if (err) {
-               Log(LOG_ERR, "Failed to initialize GnuTLS: %s",
-                   gnutls_strerror(err));
-               goto out;
+       if (!initialized) {
+               err = gnutls_global_init();
+               if (err) {
+                       Log(LOG_ERR, "Failed to initialize GnuTLS: %s",
+                           gnutls_strerror(err));
+                       goto out;
+               }
        }
 
        if (!ConnSSL_LoadServerKey_gnutls())
                goto out;
 
+       if (priorities_cache != NULL) {
+               gnutls_priority_deinit(priorities_cache);
+       }
        if (gnutls_priority_init(&priorities_cache, Conf_SSLOptions.CipherList,
                                 NULL) != GNUTLS_E_SUCCESS) {
                Log(LOG_ERR,
@@ -362,6 +446,9 @@ out:
                goto out;
        }
 
+       if (!ConnSSL_SetVerifyProperties_gnutls())
+               goto out;
+
        Log(LOG_INFO, "GnuTLS %s initialized.", gnutls_check_version(NULL));
        initialized = true;
        return true;
@@ -373,12 +460,49 @@ out:
 
 
 #ifdef HAVE_LIBGNUTLS
+static bool
+ConnSSL_SetVerifyProperties_gnutls(void)
+{
+       int err;
+
+       if (!Conf_SSLOptions.CAFile)
+               return true;
+
+       x509_cred_slot *slot = array_get(&x509_creds, sizeof(x509_cred_slot), x509_cred_idx);
+       gnutls_certificate_credentials_t x509_cred = slot->x509_cred;
+
+       err = gnutls_certificate_set_x509_trust_file(x509_cred,
+                                                    Conf_SSLOptions.CAFile,
+                                                    GNUTLS_X509_FMT_PEM);
+       if (err < 0) {
+               Log(LOG_ERR, "Failed to load x509 trust file %s: %s",
+                   Conf_SSLOptions.CAFile, gnutls_strerror(err));
+               return false;
+       }
+       if (Conf_SSLOptions.CRLFile) {
+               err =
+                   gnutls_certificate_set_x509_crl_file(x509_cred,
+                                                        Conf_SSLOptions.CRLFile,
+                                                        GNUTLS_X509_FMT_PEM);
+               if (err < 0) {
+                       Log(LOG_ERR, "Failed to load x509 crl file %s: %s",
+                           Conf_SSLOptions.CRLFile, gnutls_strerror(err));
+                       return false;
+               }
+       }
+       return true;
+}
+
+
 static bool
 ConnSSL_LoadServerKey_gnutls(void)
 {
        int err;
        const char *cert_file;
 
+       x509_cred_slot *slot = NULL;
+       gnutls_certificate_credentials_t x509_cred;
+
        err = gnutls_certificate_allocate_credentials(&x509_cred);
        if (err < 0) {
                Log(LOG_ERR, "Failed to allocate certificate credentials: %s",
@@ -386,12 +510,6 @@ ConnSSL_LoadServerKey_gnutls(void)
                return false;
        }
 
-       cert_file = Conf_SSLOptions.CertFile ? Conf_SSLOptions.CertFile:Conf_SSLOptions.KeyFile;
-       if (!cert_file) {
-               Log(LOG_ERR, "No SSL server key configured!");
-               return false;
-       }
-
        if (array_bytes(&Conf_SSLOptions.KeyFilePassword))
                Log(LOG_WARNING,
                    "Ignoring SSL \"KeyFilePassword\": Not supported by GnuTLS.");
@@ -400,15 +518,61 @@ ConnSSL_LoadServerKey_gnutls(void)
                return false;
 
        gnutls_certificate_set_dh_params(x509_cred, dh_params);
-       err = gnutls_certificate_set_x509_key_file(x509_cred, cert_file, Conf_SSLOptions.KeyFile, GNUTLS_X509_FMT_PEM);
-       if (err < 0) {
-               Log(LOG_ERR,
-                   "Failed to set certificate key file (cert %s, key %s): %s",
-                   cert_file,
-                   Conf_SSLOptions.KeyFile ? Conf_SSLOptions.KeyFile : "(NULL)",
-                   gnutls_strerror(err));
-               return false;
+       gnutls_certificate_set_flags(x509_cred, GNUTLS_CERTIFICATE_VERIFY_CRLS);
+
+       cert_file = Conf_SSLOptions.CertFile ?
+                       Conf_SSLOptions.CertFile : Conf_SSLOptions.KeyFile;
+       if (Conf_SSLOptions.KeyFile) {
+               err = gnutls_certificate_set_x509_key_file(x509_cred, cert_file,
+                                                          Conf_SSLOptions.KeyFile,
+                                                          GNUTLS_X509_FMT_PEM);
+               if (err < 0) {
+                       Log(LOG_ERR,
+                           "Failed to set certificate key file (cert %s, key %s): %s",
+                           cert_file,
+                           Conf_SSLOptions.KeyFile ? Conf_SSLOptions.KeyFile : "(NULL)",
+                           gnutls_strerror(err));
+                       return false;
+               }
+       }
+
+       /* Free currently active x509 context (if any) unless it is still in use */
+       slot = array_get(&x509_creds, sizeof(x509_cred_slot), x509_cred_idx);
+       if ((slot != NULL) && (slot->refcnt <= 0) && (slot->x509_cred != NULL)) {
+               LogDebug("Discarding X509 certificate credentials from slot %zd.",
+                        x509_cred_idx);
+               gnutls_certificate_free_keys(slot->x509_cred);
+               gnutls_certificate_free_credentials(slot->x509_cred);
+               slot->x509_cred = NULL;
+               gnutls_dh_params_deinit(slot->dh_params);
+               slot->dh_params = NULL;
+               slot->refcnt = 0;
        }
+
+       /* Find free slot */
+       x509_cred_idx = (size_t) -1;
+       size_t i;
+       for (slot = array_start(&x509_creds), i = 0;
+            i < array_length(&x509_creds, sizeof(x509_cred_slot));
+            slot++, i++) {
+               if (slot->refcnt <= 0) {
+                       x509_cred_idx = i;
+                       break;
+               }
+       }
+       /* ... allocate new slot otherwise. */
+       if (x509_cred_idx == (size_t) -1) {
+               x509_cred_idx = array_length(&x509_creds, sizeof(x509_cred_slot));
+               slot = array_alloc(&x509_creds, sizeof(x509_cred_slot), x509_cred_idx);
+               if (slot == NULL) {
+                       Log(LOG_ERR, "Failed to allocate new slot for certificate credentials");
+                       return false;
+               }
+       }
+       LogDebug("Storing new X509 certificate credentials in slot %zd.", x509_cred_idx);
+       slot->x509_cred = x509_cred;
+       slot->refcnt = 0;
+
        return true;
 }
 #endif
@@ -421,14 +585,12 @@ ConnSSL_LoadServerKey_openssl(SSL_CTX *ctx)
        char *cert_key;
 
        assert(ctx);
-       if (!Conf_SSLOptions.KeyFile) {
-               Log(LOG_ERR, "No SSL server key configured!");
-               return false;
-       }
-
        SSL_CTX_set_default_passwd_cb(ctx, pem_passwd_cb);
        SSL_CTX_set_default_passwd_cb_userdata(ctx, &Conf_SSLOptions.KeyFilePassword);
 
+       if (!Conf_SSLOptions.KeyFile)
+               return true;
+
        if (SSL_CTX_use_PrivateKey_file(ctx, Conf_SSLOptions.KeyFile, SSL_FILETYPE_PEM) != 1) {
                array_free_wipe(&Conf_SSLOptions.KeyFilePassword);
                LogOpenSSLError("Failed to add private key", Conf_SSLOptions.KeyFile);
@@ -459,6 +621,56 @@ ConnSSL_LoadServerKey_openssl(SSL_CTX *ctx)
 }
 
 
+static bool
+ConnSSL_SetVerifyProperties_openssl(SSL_CTX * ctx)
+{
+       X509_STORE *store = NULL;
+       X509_LOOKUP *lookup;
+       bool ret = false;
+
+       if (!Conf_SSLOptions.CAFile)
+               return true;
+
+       if (SSL_CTX_load_verify_locations(ctx, Conf_SSLOptions.CAFile, NULL) !=
+           1) {
+               LogOpenSSLError("SSL_CTX_load_verify_locations", NULL);
+               goto out;
+       }
+
+       if (Conf_SSLOptions.CRLFile) {
+               X509_VERIFY_PARAM *param = X509_VERIFY_PARAM_new();
+               X509_VERIFY_PARAM_set_flags(param, X509_V_FLAG_CRL_CHECK);
+               SSL_CTX_set1_param(ctx, param);
+
+               store = SSL_CTX_get_cert_store(ctx);
+               assert(store);
+               lookup = X509_STORE_add_lookup(store, X509_LOOKUP_file());
+               if (!lookup) {
+                       LogOpenSSLError("X509_STORE_add_lookup",
+                                       Conf_SSLOptions.CRLFile);
+                       goto out;
+               }
+
+               if (X509_load_crl_file
+                   (lookup, Conf_SSLOptions.CRLFile, X509_FILETYPE_PEM) != 1) {
+                       LogOpenSSLError("X509_load_crl_file",
+                                       Conf_SSLOptions.CRLFile);
+                       goto out;
+               }
+       }
+
+       SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER|SSL_VERIFY_CLIENT_ONCE,
+                          Verify_openssl);
+       SSL_CTX_set_verify_depth(ctx, MAX_CERT_CHAIN_LENGTH);
+       ret = true;
+out:
+       if (Conf_SSLOptions.CRLFile)
+               free(Conf_SSLOptions.CRLFile);
+       Conf_SSLOptions.CRLFile = NULL;
+       return ret;
+}
+
+
 #endif
 static bool
 ConnSSL_Init_SSL(CONNECTION *c)
@@ -510,8 +722,13 @@ ConnSSL_Init_SSL(CONNECTION *c)
                                 (gnutls_transport_ptr_t) (long) c->sock);
        gnutls_certificate_server_set_request(c->ssl_state.gnutls_session,
                                              GNUTLS_CERT_REQUEST);
+
+       LogDebug("Using X509 credentials from slot %zd.", x509_cred_idx);
+       c->ssl_state.x509_cred_idx = x509_cred_idx;
+       x509_cred_slot *slot = array_get(&x509_creds, sizeof(x509_cred_slot), x509_cred_idx);
+       slot->refcnt++;
        ret = gnutls_credentials_set(c->ssl_state.gnutls_session,
-                                    GNUTLS_CRD_CERTIFICATE, x509_cred);
+                                    GNUTLS_CRD_CERTIFICATE, slot->x509_cred);
        if (ret != 0) {
                Log(LOG_ERR, "Failed to set SSL credentials: %s",
                    gnutls_strerror(ret));
@@ -525,27 +742,45 @@ ConnSSL_Init_SSL(CONNECTION *c)
 
 
 bool
-ConnSSL_PrepareConnect(CONNECTION *c, UNUSED CONF_SERVER *s)
+ConnSSL_PrepareConnect(CONNECTION * c, CONF_SERVER * s)
 {
        bool ret;
 #ifdef HAVE_LIBGNUTLS
        int err;
 
+       (void)s;
        err = gnutls_init(&c->ssl_state.gnutls_session, GNUTLS_CLIENT);
        if (err) {
                Log(LOG_ERR, "Failed to initialize new SSL session: %s",
                    gnutls_strerror(err));
                return false;
-        }
+       }
 #endif
        ret = ConnSSL_Init_SSL(c);
        if (!ret)
                return false;
        Conn_OPTION_ADD(c, CONN_SSL_CONNECT);
+
 #ifdef HAVE_LIBSSL
        assert(c->ssl_state.ssl);
-       SSL_set_verify(c->ssl_state.ssl, SSL_VERIFY_NONE, NULL);
+
+       X509_VERIFY_PARAM *param = SSL_get0_param(c->ssl_state.ssl);
+       X509_VERIFY_PARAM_set_hostflags(param, X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS);
+       int err = X509_VERIFY_PARAM_set1_host(param, s->host, 0);
+       if (err != 1) {
+               Log(LOG_ERR,
+                   "Cannot set up hostname verification for '%s': %u",
+                   s->host, err);
+               return false;
+       }
+
+       if (s->SSLVerify)
+               SSL_set_verify(c->ssl_state.ssl, SSL_VERIFY_PEER,
+                              Verify_openssl);
+       else
+               SSL_set_verify(c->ssl_state.ssl, SSL_VERIFY_NONE, NULL);
 #endif
+
        return true;
 }
 
@@ -602,9 +837,12 @@ ConnSSL_HandleError(CONNECTION * c, const int code, const char *fname)
                                    "SSL error, client disconnected [in %s()]!",
                                    fname);
                                break;
-                       case -1:        /* low level socket I/O error, check errno */
-                               Log(LOG_ERR, "SSL error: %s [in %s()]!",
-                                   strerror(real_errno), fname);
+                       case -1:
+                               /* Low level socket I/O error, check errno. But
+                                * we don't need to log this here, the generic
+                                * connection layer will take care of it. */
+                               LogDebug("SSL error: %s [in %s()]!",
+                                        strerror(real_errno), fname);
                        }
                }
                break;
@@ -632,8 +870,10 @@ ConnSSL_HandleError(CONNECTION * c, const int code, const char *fname)
        default:
                assert(code < 0);
                if (gnutls_error_is_fatal(code)) {
-                       Log(LOG_ERR, "SSL error: %s [%s].",
-                           gnutls_strerror(code), fname);
+                       /* We don't need to log this here, the generic
+                        * connection layer will take care of it. */
+                       LogDebug("SSL error: %s [%s].",
+                                gnutls_strerror(code), fname);
                        ConnSSL_Free(c);
                        return -1;
                }
@@ -643,18 +883,114 @@ ConnSSL_HandleError(CONNECTION * c, const int code, const char *fname)
 }
 
 
+#ifdef HAVE_LIBGNUTLS
+static void *
+LogMalloc(size_t s)
+{
+       void *mem = malloc(s);
+       if (!mem)
+               Log(LOG_ERR, "Out of memory: Could not allocate %lu byte",
+                   (unsigned long)s);
+       return mem;
+}
+
+
+static void
+LogGnuTLS_CertInfo(int level, gnutls_x509_crt_t cert, const char *msg)
+{
+       char *dn, *issuer_dn;
+       size_t size = 0;
+       int err = gnutls_x509_crt_get_dn(cert, NULL, &size);
+       if (size == 0) {
+               Log(LOG_ERR, "gnutls_x509_crt_get_dn: size == 0");
+               return;
+       }
+       if (err && err != GNUTLS_E_SHORT_MEMORY_BUFFER)
+               goto err_crt_get;
+       dn = LogMalloc(size);
+       if (!dn)
+               return;
+       err = gnutls_x509_crt_get_dn(cert, dn, &size);
+       if (err)
+               goto err_crt_get;
+       gnutls_x509_crt_get_issuer_dn(cert, NULL, &size);
+       assert(size);
+       issuer_dn = LogMalloc(size);
+       if (!issuer_dn) {
+               Log(level, "%s: Distinguished Name \"%s\".", msg, dn);
+               free(dn);
+               return;
+       }
+       gnutls_x509_crt_get_issuer_dn(cert, issuer_dn, &size);
+       Log(level, "%s: Distinguished Name \"%s\", Issuer \"%s\".", msg, dn,
+           issuer_dn);
+       free(dn);
+       free(issuer_dn);
+       return;
+
+      err_crt_get:
+       Log(LOG_ERR, "gnutls_x509_crt_get_dn: %s", gnutls_strerror(err));
+       return;
+}
+#endif
+
+
 static void
-ConnSSL_LogCertInfo( CONNECTION *)
+ConnSSL_LogCertInfo( CONNECTION * c, bool connect)
 {
+       bool cert_seen = false, cert_ok = false;
+       char msg[128];
 #ifdef HAVE_LIBSSL
+       const char *comp_alg = "no compression";
+       const void *comp;
+       X509 *peer_cert = NULL;
        SSL *ssl = c->ssl_state.ssl;
 
        assert(ssl);
 
-       Log(LOG_INFO, "Connection %d: initialized %s using cipher %s.",
-               c->sock, SSL_get_version(ssl), SSL_get_cipher(ssl));
+       comp = SSL_get_current_compression(ssl);
+       if (comp)
+               comp_alg = SSL_COMP_get_name(comp);
+       Log(LOG_INFO, "Connection %d: initialized %s using cipher %s, %s.",
+           c->sock, SSL_get_version(ssl), SSL_get_cipher(ssl), comp_alg);
+       peer_cert = SSL_get_peer_certificate(ssl);
+       if (peer_cert) {
+               cert_seen = true;
+
+               if (connect) {
+                       /* Outgoing connection. Verify the remote server! */
+                       int err = SSL_get_verify_result(ssl);
+                       if (err == X509_V_OK) {
+                               const char *peername = SSL_get0_peername(ssl);
+                               if (peername != NULL)
+                                       cert_ok = true;
+                               LogDebug("X509_V_OK, peername = '%s'", peername);
+                       } else
+                               Log(LOG_WARNING, "Certificate validation failed: %s!",
+                                   X509_verify_cert_error_string(err));
+
+                       snprintf(msg, sizeof(msg), "Got %svalid server certificate",
+                                cert_ok ? "" : "in");
+                       LogOpenSSL_CertInfo(LOG_INFO, peer_cert, msg);
+               } else {
+                       /* Incoming connection.
+                        * Accept all certificates, don't depend on their
+                        * validity: for example, we don't know the hostname
+                        * to check, because we not yet even know if this is a
+                        * server connection at all and if so, which one, so we
+                        * don't know a host name to look for. On the other
+                        * hand we want client certificates, for example for
+                        * "CertFP" authentication with services ... */
+                       LogOpenSSL_CertInfo(LOG_INFO, peer_cert,
+                                           "Got unchecked peer certificate");
+               }
+
+               X509_free(peer_cert);
+       }
 #endif
 #ifdef HAVE_LIBGNUTLS
+       unsigned int status;
+       gnutls_credentials_type_t cred;
        gnutls_session_t sess = c->ssl_state.gnutls_session;
        gnutls_cipher_algorithm_t cipher = gnutls_cipher_get(sess);
 
@@ -663,7 +999,86 @@ ConnSSL_LogCertInfo( CONNECTION *c )
            gnutls_protocol_get_name(gnutls_protocol_get_version(sess)),
            gnutls_cipher_get_name(cipher),
            gnutls_mac_get_name(gnutls_mac_get(sess)));
+       cred = gnutls_auth_get_type(c->ssl_state.gnutls_session);
+       if (cred == GNUTLS_CRD_CERTIFICATE) {
+               gnutls_x509_crt_t cert;
+               unsigned cert_list_size;
+               const gnutls_datum_t *cert_list =
+                   gnutls_certificate_get_peers(sess, &cert_list_size);
+
+               if (!cert_list || cert_list_size == 0)
+                       goto done_cn_validation;
+
+               cert_seen = true;
+               int err = gnutls_x509_crt_init(&cert);
+               if (err < 0) {
+                       Log(LOG_ERR,
+                           "Failed to initialize x509 certificate: %s",
+                           gnutls_strerror(err));
+                       goto done_cn_validation;
+               }
+               err = gnutls_x509_crt_import(cert, cert_list,
+                                          GNUTLS_X509_FMT_DER);
+               if (err < 0) {
+                       Log(LOG_ERR, "Failed to parse the certificate: %s",
+                           gnutls_strerror(err));
+                       goto done_cn_validation;
+               }
+
+               if (connect) {
+                       int verify =
+                           gnutls_certificate_verify_peers2(c->
+                                                            ssl_state.gnutls_session,
+                                                            &status);
+                       if (verify < 0) {
+                               Log(LOG_ERR,
+                                   "gnutls_certificate_verify_peers2 failed: %s",
+                                   gnutls_strerror(verify));
+                               goto done_cn_validation;
+                       } else if (status) {
+                               gnutls_datum_t out;
+
+                               if (gnutls_certificate_verification_status_print
+                                   (status, gnutls_certificate_type_get(sess), &out,
+                                    0) == GNUTLS_E_SUCCESS) {
+                                       Log(LOG_ERR,
+                                           "Certificate validation failed: %s",
+                                           out.data);
+                                       gnutls_free(out.data);
+                               }
+                       }
+
+                       err = gnutls_x509_crt_check_hostname(cert, c->host);
+                       if (err == 0)
+                               Log(LOG_ERR,
+                                   "Failed to verify the hostname, expected \"%s\"",
+                                   c->host);
+                       else
+                               cert_ok = verify == 0 && status == 0;
+
+                       snprintf(msg, sizeof(msg), "Got %svalid server certificate",
+                               cert_ok ? "" : "in");
+                       LogGnuTLS_CertInfo(LOG_INFO, cert, msg);
+               } else {
+                       /* Incoming connection. Please see comments for OpenSSL! */
+                       LogGnuTLS_CertInfo(LOG_INFO, cert,
+                                           "Got unchecked peer certificate");
+               }
+
+               gnutls_x509_crt_deinit(cert);
+done_cn_validation:
+               ;
+       }
 #endif
+       /*
+        * can be used later to check if connection was authenticated, e.g.
+        * if inbound connection tries to register itself as server.
+        * Could also restrict /OPER to authenticated connections, etc.
+        */
+       if (cert_ok)
+               Conn_OPTION_ADD(c, CONN_SSL_PEERCERT_OK);
+       if (!cert_seen)
+               Log(LOG_INFO, "Peer did not present a certificate.");
 }
 
 
@@ -802,7 +1217,7 @@ ConnectAccept( CONNECTION *c, bool connect)
        (void)ConnSSL_InitCertFp(c);
 
        Conn_OPTION_DEL(c, (CONN_SSL_WANT_WRITE|CONN_SSL_WANT_READ|CONN_SSL_CONNECT));
-       ConnSSL_LogCertInfo(c);
+       ConnSSL_LogCertInfo(c, connect);
 
        Conn_StartLogin(CONNECTION2ID(c));
        return 1;