SSL: ssl_reject_handshake directive (ticket #195).

In some cases it might be needed to reject SSL handshake based on SNI
server name provided, for example, to make sure an invalid certificate
is not returned to clients trying to contact a name-based virtual server
without SSL configured.  Previously, a "ssl_ciphers aNULL;" was used for
this.  This workaround, however, is not compatible with TLSv1.3, in
particular, when using BoringSSL, where it is not possible to configure
TLSv1.3 ciphers at all.

With this change, the ssl_reject_handshake directive is introduced,
which instructs nginx to reject SSL handshakes with an "unrecognized_name"
alert in a particular server block.

For example, to reject handshake with names other than example.com,
one can use the following configuration:

    server {
        listen 443 ssl;
        ssl_reject_handshake on;
    }

    server {
        listen 443 ssl;
        server_name example.com;
        ssl_certificate example.com.crt;
        ssl_certificate_key example.com.key;
    }

The following configuration can be used to reject all SSL handshakes
without SNI server name provided:

    server {
        listen 443 ssl;
        ssl_reject_handshake on;
    }

    server {
        listen 443 ssl;
        server_name ~^;
        ssl_certificate example.crt;
        ssl_certificate_key example.key;
    }

Additionally, the ssl_reject_handshake directive makes configuring
certificates for the default server block optional.  If no certificates
are configured in the default server for a given listening socket,
certificates must be defined in all non-default server blocks with
the listening socket in question.

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index dfb816055ad274f8f941396f2031409d16e04d4a..2eef87e5e8464d7355e1eaf1e21b99bd51c2d0b5 100644 (file)
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -1793,6 +1793,13 @@ ngx_ssl_handshake(ngx_connection_t *c)
         return NGX_ERROR;
     }
 
+    if (c->ssl->handshake_rejected) {
+        ngx_connection_error(c, err, "handshake rejected");
+        ERR_clear_error();
+
+        return NGX_ERROR;
+    }
+
     c->read->error = 1;
 
     ngx_ssl_connection_error(c, sslerr, err, "SSL_do_handshake() failed");
@@ -3354,8 +3361,9 @@ ngx_ssl_session_id_context(ngx_ssl_t *ssl, ngx_str_t *sess_ctx,
         }
     }
 
-    if (SSL_CTX_get_ex_data(ssl->ctx, ngx_ssl_certificate_index) == NULL) {
-
+    if (SSL_CTX_get_ex_data(ssl->ctx, ngx_ssl_certificate_index) == NULL
+        && certificates != NULL)
+    {
         /*
          * If certificates are loaded dynamically, we use certificate
          * names as specified in the configuration (with variables).

diff --git a/src/event/ngx_event_openssl.h b/src/event/ngx_event_openssl.h
index 821bb13d1c11738f262d67ace345db9ed71123a0..329760d0937350b92075499c2fb16d86772c0f39 100644 (file)
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -95,6 +95,7 @@ struct ngx_ssl_connection_s {
     u_char                      early_buf;
 
     unsigned                    handshaked:1;
+    unsigned                    handshake_rejected:1;
     unsigned                    renegotiation:1;
     unsigned                    buffer:1;
     unsigned                    no_wait_shutdown:1;

diff --git a/src/http/modules/ngx_http_ssl_module.c b/src/http/modules/ngx_http_ssl_module.c
index 2702f1e20b04333a6e33f85e9c100eacaa86781e..e062b03a116cecfb72f0941c827681d4121ace9f 100644 (file)
--- a/src/http/modules/ngx_http_ssl_module.c
+++ b/src/http/modules/ngx_http_ssl_module.c
@@ -294,6 +294,13 @@ static ngx_command_t  ngx_http_ssl_commands[] = {
       offsetof(ngx_http_ssl_srv_conf_t, conf_commands),
       &ngx_http_ssl_conf_command_post },
 
+    { ngx_string("ssl_reject_handshake"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_SRV_CONF_OFFSET,
+      offsetof(ngx_http_ssl_srv_conf_t, reject_handshake),
+      NULL },
+
       ngx_null_command
 };
 
@@ -614,6 +621,7 @@ ngx_http_ssl_create_srv_conf(ngx_conf_t *cf)
     sscf->enable = NGX_CONF_UNSET;
     sscf->prefer_server_ciphers = NGX_CONF_UNSET;
     sscf->early_data = NGX_CONF_UNSET;
+    sscf->reject_handshake = NGX_CONF_UNSET;
     sscf->buffer_size = NGX_CONF_UNSET_SIZE;
     sscf->verify = NGX_CONF_UNSET_UINT;
     sscf->verify_depth = NGX_CONF_UNSET_UINT;
@@ -660,6 +668,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
                          prev->prefer_server_ciphers, 0);
 
     ngx_conf_merge_value(conf->early_data, prev->early_data, 0);
+    ngx_conf_merge_value(conf->reject_handshake, prev->reject_handshake, 0);
 
     ngx_conf_merge_bitmask_value(conf->protocols, prev->protocols,
                          (NGX_CONF_BITMASK_SET|NGX_SSL_TLSv1
@@ -707,38 +716,35 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
 
     if (conf->enable) {
 
-        if (conf->certificates == NULL) {
-            ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
-                          "no \"ssl_certificate\" is defined for "
-                          "the \"ssl\" directive in %s:%ui",
-                          conf->file, conf->line);
-            return NGX_CONF_ERROR;
-        }
+        if (conf->certificates) {
+            if (conf->certificate_keys == NULL) {
+                ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
+                              "no \"ssl_certificate_key\" is defined for "
+                              "the \"ssl\" directive in %s:%ui",
+                              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 \"ssl\" directive in %s:%ui",
-                          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 \"ssl\" directive in %s:%ui",
+                              ((ngx_str_t *) conf->certificates->elts)
+                              + conf->certificates->nelts - 1,
+                              conf->file, conf->line);
+                return NGX_CONF_ERROR;
+            }
 
-        if (conf->certificate_keys->nelts < conf->certificates->nelts) {
+        } else if (!conf->reject_handshake) {
             ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
-                          "no \"ssl_certificate_key\" is defined "
-                          "for certificate \"%V\" and "
+                          "no \"ssl_certificate\" is defined for "
                           "the \"ssl\" directive in %s:%ui",
-                          ((ngx_str_t *) conf->certificates->elts)
-                          + conf->certificates->nelts - 1,
                           conf->file, conf->line);
             return NGX_CONF_ERROR;
         }
 
-    } else {
-
-        if (conf->certificates == NULL) {
-            return NGX_CONF_OK;
-        }
+    } else if (conf->certificates) {
 
         if (conf->certificate_keys == NULL
             || conf->certificate_keys->nelts < conf->certificates->nelts)
@@ -750,6 +756,9 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
                           + conf->certificates->nelts - 1);
             return NGX_CONF_ERROR;
         }
+
+    } else if (!conf->reject_handshake) {
+        return NGX_CONF_OK;
     }
 
     if (ngx_ssl_create(&conf->ssl, conf->protocols, conf) != NGX_OK) {
@@ -808,7 +817,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
         return NGX_CONF_ERROR;
 #endif
 
-    } else {
+    } else if (conf->certificates) {
 
         /* configure certificates */
 
@@ -947,6 +956,10 @@ ngx_http_ssl_compile_certificates(ngx_conf_t *cf,
     ngx_http_complex_value_t          *cv;
     ngx_http_compile_complex_value_t   ccv;
 
+    if (conf->certificates == NULL) {
+        return NGX_OK;
+    }
+
     cert = conf->certificates->elts;
     key = conf->certificate_keys->elts;
     nelts = conf->certificates->nelts;
@@ -1327,7 +1340,33 @@ ngx_http_ssl_init(ngx_conf_t *cf)
             cscf = addr[a].default_server;
             sscf = cscf->ctx->srv_conf[ngx_http_ssl_module.ctx_index];
 
-            if (sscf->certificates == NULL) {
+            if (sscf->certificates) {
+                continue;
+            }
+
+            if (!sscf->reject_handshake) {
+                ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
+                              "no \"ssl_certificate\" is defined for "
+                              "the \"listen ... ssl\" directive in %s:%ui",
+                              cscf->file_name, cscf->line);
+                return NGX_ERROR;
+            }
+
+            /*
+             * if no certificates are defined in the default server,
+             * check all non-default server blocks
+             */
+
+            cscfp = addr[a].servers.elts;
+            for (s = 0; s < addr[a].servers.nelts; s++) {
+
+                cscf = cscfp[s];
+                sscf = cscf->ctx->srv_conf[ngx_http_ssl_module.ctx_index];
+
+                if (sscf->certificates || sscf->reject_handshake) {
+                    continue;
+                }
+
                 ngx_log_error(NGX_LOG_EMERG, cf->log, 0,
                               "no \"ssl_certificate\" is defined for "
                               "the \"listen ... ssl\" directive in %s:%ui",

diff --git a/src/http/modules/ngx_http_ssl_module.h b/src/http/modules/ngx_http_ssl_module.h
index 127570332a5ca343cffc6c3d053154df1484938f..7ab0f7eae28f7cd9eba52106a38ae8c811c39995 100644 (file)
--- a/src/http/modules/ngx_http_ssl_module.h
+++ b/src/http/modules/ngx_http_ssl_module.h
@@ -21,6 +21,7 @@ typedef struct {
 
     ngx_flag_t                      prefer_server_ciphers;
     ngx_flag_t                      early_data;
+    ngx_flag_t                      reject_handshake;
 
     ngx_uint_t                      protocols;
 

diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index 2a0528c68345bebbf4d8bfdaf00a10c87adecb96..204a9399de3b790038797a5be52d6e3eb1caa91b 100644 (file)
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -871,10 +871,14 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
         return SSL_TLSEXT_ERR_ALERT_FATAL;
     }
 
+    hc = c->data;
+
     servername = SSL_get_servername(ssl_conn, TLSEXT_NAMETYPE_host_name);
 
     if (servername == NULL) {
-        return SSL_TLSEXT_ERR_OK;
+        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
+                       "SSL server name: null");
+        goto done;
     }
 
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, c->log, 0,
@@ -883,7 +887,7 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
     host.len = ngx_strlen(servername);
 
     if (host.len == 0) {
-        return SSL_TLSEXT_ERR_OK;
+        goto done;
     }
 
     host.data = (u_char *) servername;
@@ -891,32 +895,27 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
     rc = ngx_http_validate_host(&host, c->pool, 1);
 
     if (rc == NGX_ERROR) {
-        *ad = SSL_AD_INTERNAL_ERROR;
-        return SSL_TLSEXT_ERR_ALERT_FATAL;
+        goto error;
     }
 
     if (rc == NGX_DECLINED) {
-        return SSL_TLSEXT_ERR_OK;
+        goto done;
     }
 
-    hc = c->data;
-
     rc = ngx_http_find_virtual_server(c, hc->addr_conf->virtual_names, &host,
                                       NULL, &cscf);
 
     if (rc == NGX_ERROR) {
-        *ad = SSL_AD_INTERNAL_ERROR;
-        return SSL_TLSEXT_ERR_ALERT_FATAL;
+        goto error;
     }
 
     if (rc == NGX_DECLINED) {
-        return SSL_TLSEXT_ERR_OK;
+        goto done;
     }
 
     hc->ssl_servername = ngx_palloc(c->pool, sizeof(ngx_str_t));
     if (hc->ssl_servername == NULL) {
-        *ad = SSL_AD_INTERNAL_ERROR;
-        return SSL_TLSEXT_ERR_ALERT_FATAL;
+        goto error;
     }
 
     *hc->ssl_servername = host;
@@ -933,8 +932,7 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
 
     if (sscf->ssl.ctx) {
         if (SSL_set_SSL_CTX(ssl_conn, sscf->ssl.ctx) == NULL) {
-            *ad = SSL_AD_INTERNAL_ERROR;
-            return SSL_TLSEXT_ERR_ALERT_FATAL;
+            goto error;
         }
 
         /*
@@ -960,7 +958,22 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
 #endif
     }
 
+done:
+
+    sscf = ngx_http_get_module_srv_conf(hc->conf_ctx, ngx_http_ssl_module);
+
+    if (sscf->reject_handshake) {
+        c->ssl->handshake_rejected = 1;
+        *ad = SSL_AD_UNRECOGNIZED_NAME;
+        return SSL_TLSEXT_ERR_ALERT_FATAL;
+    }
+
     return SSL_TLSEXT_ERR_OK;
+
+error:
+
+    *ad = SSL_AD_INTERNAL_ERROR;
+    return SSL_TLSEXT_ERR_ALERT_FATAL;
 }
 
 #endif