OCSP stapling: ssl_stapling_verify directive.

OCSP response verification is now switched off by default to simplify
configuration, and the ssl_stapling_verify allows to switch it on.

Note that for stapling OCSP response verification isn't something required
as it will be done by a client anyway.  But doing verification on a server
allows to mitigate some attack vectors, most notably stop an attacker from
presenting some specially crafted data to all site clients.

4 files changed, 22 insertions, 7 deletions

diff --git a/src/event/ngx_event_openssl.h b/src/event/ngx_event_openssl.h
index fc098da87..d1fb5739f 100644
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -106,7 +106,7 @@ ngx_int_t ngx_ssl_trusted_certificate(ngx_conf_t *cf, ngx_ssl_t *ssl,
     ngx_str_t *cert, ngx_int_t depth);
 ngx_int_t ngx_ssl_crl(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *crl);
 ngx_int_t ngx_ssl_stapling(ngx_conf_t *cf, ngx_ssl_t *ssl,
-    ngx_str_t *responder, ngx_str_t *file);
+    ngx_str_t *file, ngx_str_t *responder, ngx_uint_t verify);
 ngx_int_t ngx_ssl_stapling_resolver(ngx_conf_t *cf, ngx_ssl_t *ssl,
     ngx_resolver_t *resolver, ngx_msec_t resolver_timeout);
 RSA *ngx_ssl_rsa512_key_callback(SSL *ssl, int is_export, int key_length);
diff --git a/src/event/ngx_event_openssl_stapling.c b/src/event/ngx_event_openssl_stapling.c
index c09b9f7ec..51caea6f0 100644
--- a/src/event/ngx_event_openssl_stapling.c
+++ b/src/event/ngx_event_openssl_stapling.c
@@ -33,7 +33,8 @@ typedef struct {
 
     time_t                       valid;
 
-    ngx_uint_t                   loading;     /* unsigned:1 */
+    unsigned                     verify:1;
+    unsigned                     loading:1;
 } ngx_ssl_stapling_t;
 
 
@@ -114,8 +115,8 @@ static u_char *ngx_ssl_ocsp_log_error(ngx_log_t *log, u_char *buf, size_t len);
 
 
 ngx_int_t
-ngx_ssl_stapling(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *responder,
-    ngx_str_t *file)
+ngx_ssl_stapling(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *file,
+    ngx_str_t *responder, ngx_uint_t verify)
 {
     ngx_int_t                  rc;
     ngx_pool_cleanup_t        *cln;
@@ -144,6 +145,7 @@ ngx_ssl_stapling(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *responder,
 
     staple->ssl_ctx = ssl->ctx;
     staple->timeout = 60000;
+    staple->verify = verify;
 
     if (file->len) {
         /* use OCSP response from the file */
@@ -588,7 +590,10 @@ ngx_ssl_stapling_ocsp_handler(ngx_ssl_ocsp_ctx_t *ctx)
     chain = staple->ssl_ctx->extra_certs;
 #endif
 
-    if (OCSP_basic_verify(basic, chain, store, OCSP_TRUSTOTHER) != 1) {
+    if (OCSP_basic_verify(basic, chain, store,
+                          staple->verify ? OCSP_TRUSTOTHER : OCSP_NOVERIFY)
+        != 1)
+    {
         ngx_ssl_error(NGX_LOG_ERR, ctx->log, 0,
                       "OCSP_basic_verify() failed");
         goto error;
diff --git a/src/http/modules/ngx_http_ssl_module.c b/src/http/modules/ngx_http_ssl_module.c
index e49c3edb7..0073dba3c 100644
--- a/src/http/modules/ngx_http_ssl_module.c
+++ b/src/http/modules/ngx_http_ssl_module.c
@@ -182,6 +182,13 @@ static ngx_command_t  ngx_http_ssl_commands[] = {
       offsetof(ngx_http_ssl_srv_conf_t, stapling_responder),
       NULL },
 
+    { ngx_string("ssl_stapling_verify"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_SRV_CONF_OFFSET,
+      offsetof(ngx_http_ssl_srv_conf_t, stapling_verify),
+      NULL },
+
       ngx_null_command
 };
 
@@ -370,6 +377,7 @@ ngx_http_ssl_create_srv_conf(ngx_conf_t *cf)
     sscf->builtin_session_cache = NGX_CONF_UNSET;
     sscf->session_timeout = NGX_CONF_UNSET;
     sscf->stapling = NGX_CONF_UNSET;
+    sscf->stapling_verify = NGX_CONF_UNSET;
 
     return sscf;
 }
@@ -424,6 +432,7 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_str_value(conf->ciphers, prev->ciphers, NGX_DEFAULT_CIPHERS);
 
     ngx_conf_merge_value(conf->stapling, prev->stapling, 0);
+    ngx_conf_merge_value(conf->stapling_verify, prev->stapling_verify, 0);
     ngx_conf_merge_str_value(conf->stapling_file, prev->stapling_file, "");
     ngx_conf_merge_str_value(conf->stapling_responder,
                          prev->stapling_responder, "");
@@ -565,8 +574,8 @@ ngx_http_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
 
     if (conf->stapling) {
 
-        if (ngx_ssl_stapling(cf, &conf->ssl, &conf->stapling_responder,
-                             &conf->stapling_file)
+        if (ngx_ssl_stapling(cf, &conf->ssl, &conf->stapling_file,
+                             &conf->stapling_responder, conf->stapling_verify)
             != NGX_OK)
         {
             return NGX_CONF_ERROR;
diff --git a/src/http/modules/ngx_http_ssl_module.h b/src/http/modules/ngx_http_ssl_module.h
index b9037589f..c4c576ef6 100644
--- a/src/http/modules/ngx_http_ssl_module.h
+++ b/src/http/modules/ngx_http_ssl_module.h
@@ -43,6 +43,7 @@ typedef struct {
     ngx_shm_zone_t                 *shm_zone;
 
     ngx_flag_t                      stapling;
+    ngx_flag_t                      stapling_verify;
     ngx_str_t                       stapling_file;
     ngx_str_t                       stapling_responder;