[PATCH 11 of 11] SSL: automatic rotation of session ticket keys
Maxim Dounin
mdounin at mdounin.ru
Fri Aug 26 03:01:18 UTC 2022
# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1661481958 -10800
# Fri Aug 26 05:45:58 2022 +0300
# Node ID 5c26fe5f6ab0bf4c0d18cae8f6f6483348243d4b
# Parent 2487bf5766f79c813b3397b3bb897424c3590445
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.
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
@@ -74,6 +74,7 @@ static void ngx_ssl_session_rbtree_inser
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
@@ -3767,6 +3768,9 @@ ngx_ssl_session_cache_init(ngx_shm_zone_
ngx_queue_init(&cache->expire_queue);
+ cache->ticket_keys[0].expire = 0;
+ cache->ticket_keys[1].expire = 0;
+
len = sizeof(" in SSL session shared cache \"\"") + shm_zone->shm.name.len;
shpool->log_ctx = ngx_slab_alloc(shpool, len);
@@ -4234,11 +4238,13 @@ ngx_ssl_session_ticket_keys(ngx_conf_t *
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;
@@ -4252,6 +4258,34 @@ ngx_ssl_session_ticket_keys(ngx_conf_t *
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++) {
@@ -4306,6 +4340,8 @@ ngx_ssl_session_ticket_keys(ngx_conf_t *
goto failed;
}
+ key->shared = 0;
+
if (size == 48) {
key->size = 48;
ngx_memcpy(key->name, buf, 16);
@@ -4327,22 +4363,6 @@ ngx_ssl_session_ticket_keys(ngx_conf_t *
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:
@@ -4375,6 +4395,10 @@ ngx_ssl_ticket_key_callback(ngx_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
@@ -4493,6 +4517,113 @@ ngx_ssl_ticket_key_callback(ngx_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
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -147,25 +147,24 @@ struct ngx_ssl_sess_id_s {
typedef struct {
+ 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;
+
+
+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;
-#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];
-} ngx_ssl_ticket_key_t;
-
-#endif
-
-
#define NGX_SSL_SSLv2 0x0002
#define NGX_SSL_SSLv3 0x0004
#define NGX_SSL_TLSv1 0x0008
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