[nginx] SSL: session id context now includes certificate hash.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/1ee1db30c9b9
branches:  stable-1.6
changeset: 5841:1ee1db30c9b9
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Mon Sep 15 17:59:47 2014 +0400
description:
SSL: session id context now includes certificate hash.

This prevents inappropriate session reuse in unrelated server{}
blocks, while preserving ability to restore sessions on other servers
when using TLS Session Tickets.

Additionally, session context is now set even if there is no session cache
configured.  This is needed as it's also used for TLS Session Tickets.

Thanks to Antoine Delignat-Lavaud and Piotr Sikora.

diffstat:

 src/event/ngx_event_openssl.c |  98 ++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 96 insertions(+), 2 deletions(-)

diffs (127 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
@@ -27,6 +27,8 @@ static void ngx_ssl_connection_error(ngx
     ngx_err_t err, char *text);
 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_int_t ngx_ssl_session_cache_init(ngx_shm_zone_t *shm_zone, void *data);
 static int ngx_ssl_new_session(ngx_ssl_conn_t *ssl_conn,
     ngx_ssl_session_t *sess);
@@ -1729,13 +1731,15 @@ ngx_ssl_session_cache(ngx_ssl_t *ssl, ng
 
     SSL_CTX_set_timeout(ssl->ctx, (long) timeout);
 
+    if (ngx_ssl_session_id_context(ssl, sess_ctx) != NGX_OK) {
+        return NGX_ERROR;
+    }
+
     if (builtin_session_cache == NGX_SSL_NO_SCACHE) {
         SSL_CTX_set_session_cache_mode(ssl->ctx, SSL_SESS_CACHE_OFF);
         return NGX_OK;
     }
 
-    SSL_CTX_set_session_id_context(ssl->ctx, sess_ctx->data, sess_ctx->len);
-
     if (builtin_session_cache == NGX_SSL_NONE_SCACHE) {
 
         /*
@@ -1792,6 +1796,96 @@ 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)
+{
+    int                   n, i;
+    X509                 *cert;
+    X509_NAME            *name;
+    EVP_MD_CTX            md;
+    unsigned int          len;
+    STACK_OF(X509_NAME)  *list;
+    u_char                buf[EVP_MAX_MD_SIZE];
+
+    /*
+     * Session ID context is set based on the string provided,
+     * the server certificate, and the client CA list.
+     */
+
+    EVP_MD_CTX_init(&md);
+
+    if (EVP_DigestInit_ex(&md, EVP_sha1(), NULL) == 0) {
+        ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                      "EVP_DigestInit_ex() failed");
+        goto failed;
+    }
+
+    if (EVP_DigestUpdate(&md, sess_ctx->data, sess_ctx->len) == 0) {
+        ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                      "EVP_DigestUpdate() failed");
+        goto failed;
+    }
+
+    cert = SSL_CTX_get_ex_data(ssl->ctx, ngx_ssl_certificate_index);
+
+    if (X509_digest(cert, EVP_sha1(), buf, &len) == 0) {
+        ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                      "X509_digest() failed");
+        goto failed;
+    }
+
+    if (EVP_DigestUpdate(&md, buf, 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) {
+        n = sk_X509_NAME_num(list);
+
+        for (i = 0; i < n; i++) {
+            name = sk_X509_NAME_value(list, i);
+
+            if (X509_NAME_digest(name, EVP_sha1(), buf, &len) == 0) {
+                ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                              "X509_NAME_digest() failed");
+                goto failed;
+            }
+
+            if (EVP_DigestUpdate(&md, buf, len) == 0) {
+                ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                              "EVP_DigestUpdate() failed");
+                goto failed;
+            }
+        }
+    }
+
+    if (EVP_DigestFinal_ex(&md, buf, &len) == 0) {
+        ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                      "EVP_DigestUpdate() failed");
+        goto failed;
+    }
+
+    EVP_MD_CTX_cleanup(&md);
+
+    if (SSL_CTX_set_session_id_context(ssl->ctx, buf, len) == 0) {
+        ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                      "SSL_CTX_set_session_id_context() failed");
+        return NGX_ERROR;
+    }
+
+    return NGX_OK;
+
+failed:
+
+    EVP_MD_CTX_cleanup(&md);
+
+    return NGX_ERROR;
+}
+
+
 ngx_int_t
 ngx_ssl_session_cache_init(ngx_shm_zone_t *shm_zone, void *data)
 {