SSL: automatic rotation of session ticket keys.

As long as ssl_session_cache in shared memory is configured, session ticket
keys are now automatically generated in shared memory, and rotated
periodically.  This can be beneficial from forward secrecy point of view,
and also avoids increased CPU usage after configuration reloads.

This also helps BoringSSL to properly resume sessions in configurations
with multiple worker processes and no ssl_session_ticket_key directives,
as BoringSSL tries to automatically rotate session ticket keys and does
this independently in different worker processes, thus breaking session
resumption between worker processes.

2 files changed, 160 insertions, 30 deletions

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index c128e96d8..ba66119b0 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -74,6 +74,7 @@ static void ngx_ssl_session_rbtree_insert_value(ngx_rbtree_node_t *temp,
 static int ngx_ssl_ticket_key_callback(ngx_ssl_conn_t *ssl_conn,
     unsigned char *name, unsigned char *iv, EVP_CIPHER_CTX *ectx,
     HMAC_CTX *hctx, int enc);
+static ngx_int_t ngx_ssl_rotate_ticket_keys(SSL_CTX *ssl_ctx, ngx_log_t *log);
 static void ngx_ssl_ticket_keys_cleanup(void *data);
 #endif
 
@@ -3770,6 +3771,9 @@ ngx_ssl_session_cache_init(ngx_shm_zone_t *shm_zone, void *data)
 
     ngx_queue_init(&cache->expire_queue);
 
+    cache->ticket_keys[0].expire = 0;
+    cache->ticket_keys[1].expire = 0;
+
     cache->fail_time = 0;
 
     len = sizeof(" in SSL session shared cache \"\"") + shm_zone->shm.name.len;
@@ -4240,11 +4244,13 @@ ngx_ssl_session_ticket_keys(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_array_t *paths)
     ngx_pool_cleanup_t    *cln;
     ngx_ssl_ticket_key_t  *key;
 
-    if (paths == NULL) {
+    if (paths == NULL
+        && SSL_CTX_get_ex_data(ssl->ctx, ngx_ssl_session_cache_index) == NULL)
+    {
         return NGX_OK;
     }
 
-    keys = ngx_array_create(cf->pool, paths->nelts,
+    keys = ngx_array_create(cf->pool, paths ? paths->nelts : 2,
                             sizeof(ngx_ssl_ticket_key_t));
     if (keys == NULL) {
         return NGX_ERROR;
@@ -4258,6 +4264,34 @@ ngx_ssl_session_ticket_keys(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_array_t *paths)
     cln->handler = ngx_ssl_ticket_keys_cleanup;
     cln->data = keys;
 
+    if (SSL_CTX_set_ex_data(ssl->ctx, ngx_ssl_ticket_keys_index, keys) == 0) {
+        ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                      "SSL_CTX_set_ex_data() failed");
+        return NGX_ERROR;
+    }
+
+    if (SSL_CTX_set_tlsext_ticket_key_cb(ssl->ctx, ngx_ssl_ticket_key_callback)
+        == 0)
+    {
+        ngx_log_error(NGX_LOG_WARN, cf->log, 0,
+                      "nginx was built with Session Tickets support, however, "
+                      "now it is linked dynamically to an OpenSSL library "
+                      "which has no tlsext support, therefore Session Tickets "
+                      "are not available");
+        return NGX_OK;
+    }
+
+    if (paths == NULL) {
+
+        /* placeholder for keys in shared memory */
+
+        key = ngx_array_push_n(keys, 2);
+        key[0].shared = 1;
+        key[1].shared = 1;
+
+        return NGX_OK;
+    }
+
     path = paths->elts;
     for (i = 0; i < paths->nelts; i++) {
 
@@ -4312,6 +4346,8 @@ ngx_ssl_session_ticket_keys(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_array_t *paths)
             goto failed;
         }
 
+        key->shared = 0;
+
         if (size == 48) {
             key->size = 48;
             ngx_memcpy(key->name, buf, 16);
@@ -4333,22 +4369,6 @@ ngx_ssl_session_ticket_keys(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_array_t *paths)
         ngx_explicit_memzero(&buf, 80);
     }
 
-    if (SSL_CTX_set_ex_data(ssl->ctx, ngx_ssl_ticket_keys_index, keys) == 0) {
-        ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
-                      "SSL_CTX_set_ex_data() failed");
-        return NGX_ERROR;
-    }
-
-    if (SSL_CTX_set_tlsext_ticket_key_cb(ssl->ctx, ngx_ssl_ticket_key_callback)
-        == 0)
-    {
-        ngx_log_error(NGX_LOG_WARN, cf->log, 0,
-                      "nginx was built with Session Tickets support, however, "
-                      "now it is linked dynamically to an OpenSSL library "
-                      "which has no tlsext support, therefore Session Tickets "
-                      "are not available");
-    }
-
     return NGX_OK;
 
 failed:
@@ -4381,6 +4401,10 @@ ngx_ssl_ticket_key_callback(ngx_ssl_conn_t *ssl_conn,
     c = ngx_ssl_get_connection(ssl_conn);
     ssl_ctx = c->ssl->session_ctx;
 
+    if (ngx_ssl_rotate_ticket_keys(ssl_ctx, c->log) != NGX_OK) {
+        return -1;
+    }
+
 #ifdef OPENSSL_NO_SHA256
     digest = EVP_sha1();
 #else
@@ -4499,6 +4523,113 @@ ngx_ssl_ticket_key_callback(ngx_ssl_conn_t *ssl_conn,
 }
 
 
+static ngx_int_t
+ngx_ssl_rotate_ticket_keys(SSL_CTX *ssl_ctx, ngx_log_t *log)
+{
+    time_t                    now, expire;
+    ngx_array_t              *keys;
+    ngx_shm_zone_t           *shm_zone;
+    ngx_slab_pool_t          *shpool;
+    ngx_ssl_ticket_key_t     *key;
+    ngx_ssl_session_cache_t  *cache;
+    u_char                    buf[80];
+
+    keys = SSL_CTX_get_ex_data(ssl_ctx, ngx_ssl_ticket_keys_index);
+    if (keys == NULL) {
+        return NGX_OK;
+    }
+
+    key = keys->elts;
+
+    if (!key[0].shared) {
+        return NGX_OK;
+    }
+
+    now = ngx_time();
+    expire = now + SSL_CTX_get_timeout(ssl_ctx);
+
+    shm_zone = SSL_CTX_get_ex_data(ssl_ctx, ngx_ssl_session_cache_index);
+
+    cache = shm_zone->data;
+    shpool = (ngx_slab_pool_t *) shm_zone->shm.addr;
+
+    ngx_shmtx_lock(&shpool->mutex);
+
+    key = cache->ticket_keys;
+
+    if (key[0].expire == 0) {
+
+        /* initialize the current key */
+
+        if (RAND_bytes(buf, 80) != 1) {
+            ngx_ssl_error(NGX_LOG_ALERT, log, 0, "RAND_bytes() failed");
+            ngx_shmtx_unlock(&shpool->mutex);
+            return NGX_ERROR;
+        }
+
+        key->shared = 1;
+        key->expire = expire;
+        key->size = 80;
+        ngx_memcpy(key->name, buf, 16);
+        ngx_memcpy(key->hmac_key, buf + 16, 32);
+        ngx_memcpy(key->aes_key, buf + 48, 32);
+
+        ngx_explicit_memzero(&buf, 80);
+
+        ngx_log_debug2(NGX_LOG_DEBUG_EVENT, log, 0,
+                       "ssl ticket key: \"%*xs\"",
+                       (size_t) 16, key->name);
+    }
+
+    if (key[1].expire < now) {
+
+        /*
+         * if the previous key is no longer needed (or not initialized),
+         * replace it with the current key and generate new current key
+         */
+
+        key[1] = key[0];
+
+        if (RAND_bytes(buf, 80) != 1) {
+            ngx_ssl_error(NGX_LOG_ALERT, log, 0, "RAND_bytes() failed");
+            ngx_shmtx_unlock(&shpool->mutex);
+            return NGX_ERROR;
+        }
+
+        key->shared = 1;
+        key->expire = expire;
+        key->size = 80;
+        ngx_memcpy(key->name, buf, 16);
+        ngx_memcpy(key->hmac_key, buf + 16, 32);
+        ngx_memcpy(key->aes_key, buf + 48, 32);
+
+        ngx_explicit_memzero(&buf, 80);
+
+        ngx_log_debug2(NGX_LOG_DEBUG_EVENT, log, 0,
+                       "ssl ticket key: \"%*xs\"",
+                       (size_t) 16, key->name);
+    }
+
+    /*
+     * update expiration of the current key: it is going to be needed
+     * at least till the session being created expires
+     */
+
+    if (expire > key[0].expire) {
+        key[0].expire = expire;
+    }
+
+    /* sync keys to the worker process memory */
+
+    ngx_memcpy(keys->elts, cache->ticket_keys,
+               2 * sizeof(ngx_ssl_ticket_key_t));
+
+    ngx_shmtx_unlock(&shpool->mutex);
+
+    return NGX_OK;
+}
+
+
 static void
 ngx_ssl_ticket_keys_cleanup(void *data)
 {
diff --git a/src/event/ngx_event_openssl.h b/src/event/ngx_event_openssl.h
index 936662127..45d8b78a7 100644
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -147,23 +147,22 @@ struct ngx_ssl_sess_id_s {
 
 
 typedef struct {
-    ngx_rbtree_t                session_rbtree;
-    ngx_rbtree_node_t           sentinel;
-    ngx_queue_t                 expire_queue;
-    time_t                      fail_time;
-} ngx_ssl_session_cache_t;
-
-
-#ifdef SSL_CTRL_SET_TLSEXT_TICKET_KEY_CB
-
-typedef struct {
-    size_t                      size;
     u_char                      name[16];
     u_char                      hmac_key[32];
     u_char                      aes_key[32];
+    time_t                      expire;
+    unsigned                    size:8;
+    unsigned                    shared:1;
 } ngx_ssl_ticket_key_t;
 
-#endif
+
+typedef struct {
+    ngx_rbtree_t                session_rbtree;
+    ngx_rbtree_node_t           sentinel;
+    ngx_queue_t                 expire_queue;
+    ngx_ssl_ticket_key_t        ticket_keys[2];
+    time_t                      fail_time;
+} ngx_ssl_session_cache_t;
 
 
 #define NGX_SSL_SSLv2    0x0002