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changeset 9457:fa9e8292a672

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SNI: using the ClientHello callback. The change introduces an SNI based virtual server selection during early ClientHello processing. The callback is available since OpenSSL 1.1.1; for older OpenSSL versions, the previous behaviour is kept. Using the ClientHello callback sets a reasonable processing order for the "server_name" TLS extension. Notably, session resumption decision now happens after applying server configuration chosen by SNI, useful with enabled verification of client certificates, which brings consistency with BoringSSL behaviour. The change supersedes and reverts a fix made in 46b9f5d38 for TLSv1.3 resumed sessions. In addition, since the callback is invoked prior to the protocol version negotiation, this makes it possible to set "ssl_protocols" on a per-virtual server basis. To keep the $ssl_server_name variable working with TLSv1.2 resumed sessions, as previously fixed in fd97b2a80, a limited server name callback is preserved in order to acknowledge the extension. Note that to allow third-party modules to properly chain the call to ngx_ssl_client_hello_callback(), the servername callback function is passed through exdata.
author Sergey Kandaurov <pluknet@nginx.com>
date Tue, 28 Jan 2025 00:53:15 +0400
parents 8eea8cb2d2a1
children a248091b0e30
files src/event/ngx_event_openssl.c src/event/ngx_event_openssl.h src/http/modules/ngx_http_ssl_module.c src/http/ngx_http_request.c src/stream/ngx_stream_ssl_module.c
diffstat 5 files changed, 166 insertions(+), 72 deletions(-) [+]
line wrap: on
line diff
--- a/src/event/ngx_event_openssl.c	Mon Sep 08 22:03:30 2025 +0800
+++ b/src/event/ngx_event_openssl.c	Tue Jan 28 00:53:15 2025 +0400
@@ -128,6 +128,7 @@
 int  ngx_ssl_ocsp_index;
 int  ngx_ssl_index;
 int  ngx_ssl_certificate_name_index;
+int  ngx_ssl_client_hello_arg_index;
 
 
 u_char  ngx_ssl_session_buffer[NGX_SSL_MAX_SESSION_SIZE];
@@ -270,6 +271,14 @@
         return NGX_ERROR;
     }
 
+    ngx_ssl_client_hello_arg_index = SSL_CTX_get_ex_new_index(0, NULL, NULL,
+                                                              NULL, NULL);
+    if (ngx_ssl_client_hello_arg_index == -1) {
+        ngx_ssl_error(NGX_LOG_ALERT, log, 0,
+                      "SSL_CTX_get_ex_new_index() failed");
+        return NGX_ERROR;
+    }
+
     return NGX_OK;
 }
 
@@ -1645,6 +1654,82 @@
 }
 
 
+void
+ngx_ssl_set_client_hello_callback(SSL_CTX *ssl_ctx,
+    ngx_ssl_client_hello_arg *cb)
+{
+#ifdef SSL_CLIENT_HELLO_SUCCESS
+
+    SSL_CTX_set_client_hello_cb(ssl_ctx, ngx_ssl_client_hello_callback, NULL);
+    SSL_CTX_set_ex_data(ssl_ctx, ngx_ssl_client_hello_arg_index, cb);
+
+#endif
+}
+
+
+#ifdef SSL_CLIENT_HELLO_SUCCESS
+
+int
+ngx_ssl_client_hello_callback(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
+{
+    u_char                    *p;
+    size_t                     len;
+    ngx_int_t                  rc;
+    ngx_str_t                  host;
+    ngx_connection_t          *c;
+    ngx_ssl_client_hello_arg  *cb;
+
+    c = ngx_ssl_get_connection(ssl_conn);
+    cb = SSL_CTX_get_ex_data(c->ssl->session_ctx,
+                             ngx_ssl_client_hello_arg_index);
+
+    if (SSL_client_hello_get0_ext(ssl_conn, TLSEXT_TYPE_server_name,
+                                  (const unsigned char **) &p, &len)
+        == 0)
+    {
+        ngx_str_null(&host);
+        goto done;
+    }
+
+    /*
+     * RFC 6066 mandates non-zero HostName length, we follow OpenSSL.
+     * No more than one ServerName is expected.
+     */
+
+    if (len < 5
+        || (size_t) (p[0] << 8) + p[1] + 2 != len
+        || p[2] != TLSEXT_NAMETYPE_host_name
+        || (size_t) (p[3] << 8) + p[4] + 2 + 3 != len)
+    {
+        *ad = SSL_AD_DECODE_ERROR;
+        return SSL_CLIENT_HELLO_ERROR;
+    }
+
+    len -= 5;
+    p += 5;
+
+    if (len > TLSEXT_MAXLEN_host_name || ngx_strlchr(p, p + len, '\0')) {
+        *ad = SSL_AD_UNRECOGNIZED_NAME;
+        return SSL_CLIENT_HELLO_ERROR;
+    }
+
+    host.len = len;
+    host.data = p;
+
+done:
+
+    rc = cb->servername(ssl_conn, ad, &host);
+
+    if (rc == SSL_TLSEXT_ERR_ALERT_FATAL) {
+        return SSL_CLIENT_HELLO_ERROR;
+    }
+
+    return SSL_CLIENT_HELLO_SUCCESS;
+}
+
+#endif
+
+
 ngx_int_t
 ngx_ssl_create_connection(ngx_ssl_t *ssl, ngx_connection_t *c, ngx_uint_t flags)
 {
--- a/src/event/ngx_event_openssl.h	Mon Sep 08 22:03:30 2025 +0800
+++ b/src/event/ngx_event_openssl.h	Tue Jan 28 00:53:15 2025 +0400
@@ -151,6 +151,7 @@
     unsigned                    in_ocsp:1;
     unsigned                    early_preread:1;
     unsigned                    write_blocked:1;
+    unsigned                    sni_accepted:1;
 };
 
 
@@ -197,6 +198,13 @@
 } ngx_ssl_session_cache_t;
 
 
+typedef int (*ngx_ssl_servername_pt)(ngx_ssl_conn_t *, int *, void *);
+
+typedef struct {
+    ngx_ssl_servername_pt       servername;
+} ngx_ssl_client_hello_arg;
+
+
 #define NGX_SSL_SSLv2    0x0002
 #define NGX_SSL_SSLv3    0x0004
 #define NGX_SSL_TLSv1    0x0008
@@ -286,6 +294,12 @@
     ngx_array_t *paths);
 ngx_int_t ngx_ssl_session_cache_init(ngx_shm_zone_t *shm_zone, void *data);
 
+void ngx_ssl_set_client_hello_callback(SSL_CTX *ssl_ctx,
+    ngx_ssl_client_hello_arg *cb);
+#ifdef SSL_CLIENT_HELLO_SUCCESS
+int ngx_ssl_client_hello_callback(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg);
+#endif
+
 ngx_int_t ngx_ssl_create_connection(ngx_ssl_t *ssl, ngx_connection_t *c,
     ngx_uint_t flags);
 
@@ -382,6 +396,7 @@
 extern int  ngx_ssl_ocsp_index;
 extern int  ngx_ssl_index;
 extern int  ngx_ssl_certificate_name_index;
+extern int  ngx_ssl_client_hello_arg_index;
 
 
 extern u_char  ngx_ssl_session_buffer[NGX_SSL_MAX_SESSION_SIZE];
--- a/src/http/modules/ngx_http_ssl_module.c	Mon Sep 08 22:03:30 2025 +0800
+++ b/src/http/modules/ngx_http_ssl_module.c	Tue Jan 28 00:53:15 2025 +0400
@@ -749,6 +749,10 @@
     cln->data = &conf->ssl;
 
 #ifdef SSL_CTRL_SET_TLSEXT_HOSTNAME
+    {
+    static ngx_ssl_client_hello_arg cb = { ngx_http_ssl_servername };
+
+    ngx_ssl_set_client_hello_callback(conf->ssl.ctx, &cb);
 
     if (SSL_CTX_set_tlsext_servername_callback(conf->ssl.ctx,
                                                ngx_http_ssl_servername)
@@ -759,7 +763,7 @@
             "dynamically to an OpenSSL library which has no tlsext support, "
             "therefore SNI is not available");
     }
-
+    }
 #endif
 
 #ifdef TLSEXT_TYPE_application_layer_protocol_negotiation
--- a/src/http/ngx_http_request.c	Mon Sep 08 22:03:30 2025 +0800
+++ b/src/http/ngx_http_request.c	Tue Jan 28 00:53:15 2025 +0400
@@ -891,27 +891,41 @@
         return SSL_TLSEXT_ERR_ALERT_FATAL;
     }
 
+    if (c->ssl->sni_accepted) {
+        return SSL_TLSEXT_ERR_OK;
+    }
+
     hc = c->data;
 
-    servername = SSL_get_servername(ssl_conn, TLSEXT_NAMETYPE_host_name);
-
-    if (servername == NULL) {
-        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
-                       "SSL server name: null");
-        goto done;
+    if (arg != NULL) {
+        host = *(ngx_str_t *) arg;
+
+        if (host.data == NULL) {
+            ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
+                           "SSL server name: null");
+            goto done;
+        }
+
+    } else {
+        servername = SSL_get_servername(ssl_conn, TLSEXT_NAMETYPE_host_name);
+
+        if (servername == NULL) {
+            ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
+                           "SSL server name: null");
+            goto done;
+        }
+
+        host.len = ngx_strlen(servername);
+        host.data = (u_char *) servername;
     }
 
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, c->log, 0,
-                   "SSL server name: \"%s\"", servername);
-
-    host.len = ngx_strlen(servername);
+                   "SSL server name: \"%V\"", &host);
 
     if (host.len == 0) {
         goto done;
     }
 
-    host.data = (u_char *) servername;
-
     rc = ngx_http_validate_host(&host, c->pool, 1);
 
     if (rc == NGX_ERROR) {
@@ -933,31 +947,6 @@
         goto done;
     }
 
-    sscf = ngx_http_get_module_srv_conf(cscf->ctx, ngx_http_ssl_module);
-
-#if (defined TLS1_3_VERSION                                                   \
-     && !defined LIBRESSL_VERSION_NUMBER && !defined OPENSSL_IS_BORINGSSL)
-
-    /*
-     * SSL_SESSION_get0_hostname() is only available in OpenSSL 1.1.1+,
-     * but servername being negotiated in every TLSv1.3 handshake
-     * is only returned in OpenSSL 1.1.1+ as well
-     */
-
-    if (sscf->verify) {
-        const char  *hostname;
-
-        hostname = SSL_SESSION_get0_hostname(SSL_get0_session(ssl_conn));
-
-        if (hostname != NULL && ngx_strcmp(hostname, servername) != 0) {
-            c->ssl->handshake_rejected = 1;
-            *ad = SSL_AD_ACCESS_DENIED;
-            return SSL_TLSEXT_ERR_ALERT_FATAL;
-        }
-    }
-
-#endif
-
     hc->ssl_servername = ngx_palloc(c->pool, sizeof(ngx_str_t));
     if (hc->ssl_servername == NULL) {
         goto error;
@@ -971,6 +960,8 @@
 
     ngx_set_connection_log(c, clcf->error_log);
 
+    sscf = ngx_http_get_module_srv_conf(cscf->ctx, ngx_http_ssl_module);
+
     c->ssl->buffer_size = sscf->buffer_size;
 
     if (sscf->ssl.ctx) {
@@ -1019,6 +1010,7 @@
         return SSL_TLSEXT_ERR_ALERT_FATAL;
     }
 
+    c->ssl->sni_accepted = 1;
     return SSL_TLSEXT_ERR_OK;
 
 error:
--- a/src/stream/ngx_stream_ssl_module.c	Mon Sep 08 22:03:30 2025 +0800
+++ b/src/stream/ngx_stream_ssl_module.c	Tue Jan 28 00:53:15 2025 +0400
@@ -555,27 +555,41 @@
         return SSL_TLSEXT_ERR_ALERT_FATAL;
     }
 
+    if (c->ssl->sni_accepted) {
+        return SSL_TLSEXT_ERR_OK;
+    }
+
     s = c->data;
 
-    servername = SSL_get_servername(ssl_conn, TLSEXT_NAMETYPE_host_name);
+    if (arg) {
+        host = *(ngx_str_t *) arg;
+
+        if (host.data == NULL) {
+            ngx_log_debug0(NGX_LOG_DEBUG_STREAM, c->log, 0,
+                           "SSL server name: null");
+            goto done;
+        }
 
-    if (servername == NULL) {
-        ngx_log_debug0(NGX_LOG_DEBUG_STREAM, c->log, 0,
-                       "SSL server name: null");
-        goto done;
+    } else {
+        servername = SSL_get_servername(ssl_conn, TLSEXT_NAMETYPE_host_name);
+
+        if (servername == NULL) {
+            ngx_log_debug0(NGX_LOG_DEBUG_STREAM, c->log, 0,
+                           "SSL server name: null");
+            goto done;
+        }
+
+        host.len = ngx_strlen(servername);
+        host.data = (u_char *) servername;
     }
 
     ngx_log_debug1(NGX_LOG_DEBUG_STREAM, c->log, 0,
-                   "SSL server name: \"%s\"", servername);
-
-    host.len = ngx_strlen(servername);
+                   "SSL server name: \"%V\"", &host);
 
     if (host.len == 0) {
         goto done;
     }
 
-    host.data = (u_char *) servername;
-
     rc = ngx_stream_validate_host(&host, c->pool, 1);
 
     if (rc == NGX_ERROR) {
@@ -596,35 +610,12 @@
         goto done;
     }
 
-    sscf = ngx_stream_get_module_srv_conf(cscf->ctx, ngx_stream_ssl_module);
-
-#if (defined TLS1_3_VERSION                                                   \
-     && !defined LIBRESSL_VERSION_NUMBER && !defined OPENSSL_IS_BORINGSSL)
-
-    /*
-     * SSL_SESSION_get0_hostname() is only available in OpenSSL 1.1.1+,
-     * but servername being negotiated in every TLSv1.3 handshake
-     * is only returned in OpenSSL 1.1.1+ as well
-     */
-
-    if (sscf->verify) {
-        const char  *hostname;
-
-        hostname = SSL_SESSION_get0_hostname(SSL_get0_session(ssl_conn));
-
-        if (hostname != NULL && ngx_strcmp(hostname, servername) != 0) {
-            c->ssl->handshake_rejected = 1;
-            *ad = SSL_AD_ACCESS_DENIED;
-            return SSL_TLSEXT_ERR_ALERT_FATAL;
-        }
-    }
-
-#endif
-
     s->srv_conf = cscf->ctx->srv_conf;
 
     ngx_set_connection_log(c, cscf->error_log);
 
+    sscf = ngx_stream_get_module_srv_conf(cscf->ctx, ngx_stream_ssl_module);
+
     if (sscf->ssl.ctx) {
         if (SSL_set_SSL_CTX(ssl_conn, sscf->ssl.ctx) == NULL) {
             goto error;
@@ -663,6 +654,7 @@
         return SSL_TLSEXT_ERR_ALERT_FATAL;
     }
 
+    c->ssl->sni_accepted = 1;
     return SSL_TLSEXT_ERR_OK;
 
 error:
@@ -1002,8 +994,14 @@
     cln->data = &conf->ssl;
 
 #ifdef SSL_CTRL_SET_TLSEXT_HOSTNAME
+    {
+    static ngx_ssl_client_hello_arg cb = { ngx_stream_ssl_servername };
+
+    ngx_ssl_set_client_hello_callback(conf->ssl.ctx, &cb);
+
     SSL_CTX_set_tlsext_servername_callback(conf->ssl.ctx,
                                            ngx_stream_ssl_servername);
+    }
 #endif
 
 #ifdef TLSEXT_TYPE_application_layer_protocol_negotiation