[nginx] SSL: adjusted session id context with dynamic certificates.

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/6708bec13757
branches:  
changeset: 7465:6708bec13757
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Mon Feb 25 16:42:54 2019 +0300
description:
SSL: adjusted session id context with dynamic certificates.

Dynamic certificates re-introduce problem with incorrect session
reuse (AKA "virtual host confusion", CVE-2014-3616), since there are
no server certificates to generate session id context from.

To prevent this, session id context is now generated from ssl_certificate
directives as specified in the configuration.  This approach prevents
incorrect session reuse in most cases, while still allowing sharing
sessions across multiple machines with ssl_session_ticket_key set as
long as configurations are identical.

diffstat:

 src/event/ngx_event_openssl.c          |  30 ++++++++++++++++++++++++++----
 src/event/ngx_event_openssl.h          |   3 ++-
 src/http/modules/ngx_http_ssl_module.c |   2 +-
 src/mail/ngx_mail_ssl_module.c         |   2 +-
 src/stream/ngx_stream_ssl_module.c     |   2 +-
 5 files changed, 31 insertions(+), 8 deletions(-)

diffs (119 lines):

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -54,7 +54,7 @@ static void ngx_ssl_connection_error(ngx
 static void ngx_ssl_clear_error(ngx_log_t *log);
 
 static ngx_int_t ngx_ssl_session_id_context(ngx_ssl_t *ssl,
-    ngx_str_t *sess_ctx);
+    ngx_str_t *sess_ctx, ngx_array_t *certificates);
 static int ngx_ssl_new_session(ngx_ssl_conn_t *ssl_conn,
     ngx_ssl_session_t *sess);
 static ngx_ssl_session_t *ngx_ssl_get_cached_session(ngx_ssl_conn_t *ssl_conn,
@@ -3013,13 +3013,14 @@ ngx_ssl_error(ngx_uint_t level, ngx_log_
 
 ngx_int_t
 ngx_ssl_session_cache(ngx_ssl_t *ssl, ngx_str_t *sess_ctx,
-    ssize_t builtin_session_cache, ngx_shm_zone_t *shm_zone, time_t timeout)
+    ngx_array_t *certificates, ssize_t builtin_session_cache,
+    ngx_shm_zone_t *shm_zone, time_t timeout)
 {
     long  cache_mode;
 
     SSL_CTX_set_timeout(ssl->ctx, (long) timeout);
 
-    if (ngx_ssl_session_id_context(ssl, sess_ctx) != NGX_OK) {
+    if (ngx_ssl_session_id_context(ssl, sess_ctx, certificates) != NGX_OK) {
         return NGX_ERROR;
     }
 
@@ -3085,11 +3086,14 @@ ngx_ssl_session_cache(ngx_ssl_t *ssl, ng
 
 
 static ngx_int_t
-ngx_ssl_session_id_context(ngx_ssl_t *ssl, ngx_str_t *sess_ctx)
+ngx_ssl_session_id_context(ngx_ssl_t *ssl, ngx_str_t *sess_ctx,
+    ngx_array_t *certificates)
 {
     int                   n, i;
     X509                 *cert;
     X509_NAME            *name;
+    ngx_str_t            *certs;
+    ngx_uint_t            k;
     EVP_MD_CTX           *md;
     unsigned int          len;
     STACK_OF(X509_NAME)  *list;
@@ -3134,6 +3138,24 @@ ngx_ssl_session_id_context(ngx_ssl_t *ss
         }
     }
 
+    if (SSL_CTX_get_ex_data(ssl->ctx, ngx_ssl_certificate_index) == NULL) {
+
+        /*
+         * If certificates are loaded dynamically, we use certificate
+         * names as specified in the configuration (with variables).
+         */
+
+        certs = certificates->elts;
+        for (k = 0; k < certificates->nelts; k++) {
+
+            if (EVP_DigestUpdate(md, certs[k].data, certs[k].len) == 0) {
+                ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                              "EVP_DigestUpdate() failed");
+                goto failed;
+            }
+        }
+    }
+
     list = SSL_CTX_get_client_CA_list(ssl->ctx);
 
     if (list != NULL) {
diff --git a/src/event/ngx_event_openssl.h b/src/event/ngx_event_openssl.h
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -192,7 +192,8 @@ ngx_int_t ngx_ssl_early_data(ngx_conf_t 
 ngx_int_t ngx_ssl_client_session_cache(ngx_conf_t *cf, ngx_ssl_t *ssl,
     ngx_uint_t enable);
 ngx_int_t ngx_ssl_session_cache(ngx_ssl_t *ssl, ngx_str_t *sess_ctx,
-    ssize_t builtin_session_cache, ngx_shm_zone_t *shm_zone, time_t timeout);
+    ngx_array_t *certificates, ssize_t builtin_session_cache,
+    ngx_shm_zone_t *shm_zone, time_t timeout);
 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);
diff --git a/src/http/modules/ngx_http_ssl_module.c b/src/http/modules/ngx_http_ssl_module.c
--- a/src/http/modules/ngx_http_ssl_module.c
+++ b/src/http/modules/ngx_http_ssl_module.c
@@ -817,7 +817,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *
     }
 
     if (ngx_ssl_session_cache(&conf->ssl, &ngx_http_ssl_sess_id_ctx,
-                              conf->builtin_session_cache,
+                              conf->certificates, conf->builtin_session_cache,
                               conf->shm_zone, conf->session_timeout)
         != NGX_OK)
     {
diff --git a/src/mail/ngx_mail_ssl_module.c b/src/mail/ngx_mail_ssl_module.c
--- a/src/mail/ngx_mail_ssl_module.c
+++ b/src/mail/ngx_mail_ssl_module.c
@@ -435,7 +435,7 @@ ngx_mail_ssl_merge_conf(ngx_conf_t *cf, 
     }
 
     if (ngx_ssl_session_cache(&conf->ssl, &ngx_mail_ssl_sess_id_ctx,
-                              conf->builtin_session_cache,
+                              conf->certificates, conf->builtin_session_cache,
                               conf->shm_zone, conf->session_timeout)
         != NGX_OK)
     {
diff --git a/src/stream/ngx_stream_ssl_module.c b/src/stream/ngx_stream_ssl_module.c
--- a/src/stream/ngx_stream_ssl_module.c
+++ b/src/stream/ngx_stream_ssl_module.c
@@ -766,7 +766,7 @@ ngx_stream_ssl_merge_conf(ngx_conf_t *cf
     }
 
     if (ngx_ssl_session_cache(&conf->ssl, &ngx_stream_ssl_sess_id_ctx,
-                              conf->builtin_session_cache,
+                              conf->certificates, conf->builtin_session_cache,
                               conf->shm_zone, conf->session_timeout)
         != NGX_OK)
     {