[nginx] SNI: using the ClientHello callback.
noreply at nginx.com
noreply at nginx.com
Thu Sep 25 15:26:03 UTC 2025
details: https://github.com/nginx/nginx/commit/0373fe5d98c1515640e74fa6f4d32fac1f1d3ab2
branches: master
commit: 0373fe5d98c1515640e74fa6f4d32fac1f1d3ab2
user: Sergey Kandaurov <pluknet at nginx.com>
date: Tue, 28 Jan 2025 00:53:15 +0400
description:
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.
---
src/event/ngx_event_openssl.c | 85 ++++++++++++++++++++++++++++++++++
src/event/ngx_event_openssl.h | 15 ++++++
src/http/modules/ngx_http_ssl_module.c | 6 ++-
src/http/ngx_http_request.c | 62 +++++++++++--------------
src/stream/ngx_stream_ssl_module.c | 68 +++++++++++++--------------
5 files changed, 165 insertions(+), 71 deletions(-)
diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index e36f30c74..d9abcd082 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -128,6 +128,7 @@ int ngx_ssl_ticket_keys_index;
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 @@ ngx_ssl_init(ngx_log_t *log)
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 @@ ngx_ssl_new_client_session(ngx_ssl_conn_t *ssl_conn, ngx_ssl_session_t *sess)
}
+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)
{
diff --git a/src/event/ngx_event_openssl.h b/src/event/ngx_event_openssl.h
index e7ccd51e8..544703f61 100644
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -151,6 +151,7 @@ struct ngx_ssl_connection_s {
unsigned in_ocsp:1;
unsigned early_preread:1;
unsigned write_blocked:1;
+ unsigned sni_accepted:1;
};
@@ -197,6 +198,13 @@ typedef struct {
} 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_int_t ngx_ssl_session_ticket_keys(ngx_conf_t *cf, ngx_ssl_t *ssl,
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_ticket_keys_index;
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];
diff --git a/src/http/modules/ngx_http_ssl_module.c b/src/http/modules/ngx_http_ssl_module.c
index fbf4ab871..3778758e2 100644
--- a/src/http/modules/ngx_http_ssl_module.c
+++ b/src/http/modules/ngx_http_ssl_module.c
@@ -749,6 +749,10 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
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 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
"dynamically to an OpenSSL library which has no tlsext support, "
"therefore SNI is not available");
}
-
+ }
#endif
#ifdef TLSEXT_TYPE_application_layer_protocol_negotiation
diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index 95cb1a133..6f6e975b7 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -891,27 +891,41 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
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 (arg != NULL) {
+ host = *(ngx_str_t *) arg;
- if (servername == NULL) {
- ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
- "SSL server name: null");
- goto done;
+ 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 @@ ngx_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
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_http_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
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 @@ done:
return SSL_TLSEXT_ERR_ALERT_FATAL;
}
+ c->ssl->sni_accepted = 1;
return SSL_TLSEXT_ERR_OK;
error:
diff --git a/src/stream/ngx_stream_ssl_module.c b/src/stream/ngx_stream_ssl_module.c
index 7ce1175f1..7bf6304e4 100644
--- a/src/stream/ngx_stream_ssl_module.c
+++ b/src/stream/ngx_stream_ssl_module.c
@@ -555,27 +555,41 @@ ngx_stream_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
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 (servername == NULL) {
- ngx_log_debug0(NGX_LOG_DEBUG_STREAM, c->log, 0,
- "SSL server name: null");
- goto done;
+ if (host.data == 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 @@ ngx_stream_ssl_servername(ngx_ssl_conn_t *ssl_conn, int *ad, void *arg)
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 @@ done:
return SSL_TLSEXT_ERR_ALERT_FATAL;
}
+ c->ssl->sni_accepted = 1;
return SSL_TLSEXT_ERR_OK;
error:
@@ -1002,8 +994,14 @@ ngx_stream_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
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
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