Further mitigation for the TLS renegotation attack, CVE-2009-3555:

* modules/ssl/ssl_engine_kernel.c (has_buffered_data): New function.
  (ssl_hook_Access): Forcibly disable keepalive for the connection if
  there is any buffered data readable from the input filter stack.

* modules/ssl/ssl_engine_io.c (ssl_io_filter_input): Ensure that the
  BIO uses blocking operations when invoked outside direct control of
  the httpd filter stack.

Thanks to Hartmut Keil <Hartmut.Keil adnovum.ch> for proposing this
technique.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@891282 13f79535-47bb-0310-9956-ffa450edef68

modules/ssl/ssl_engine_io.c

@@ -1344,9 +1344,17 @@ static apr_status_t ssl_io_filter_input(ap_filter_t *f,
     }
     else {
         /* We have no idea what you are talking about, so return an error. */
-        return APR_ENOTIMPL;
+        status = APR_ENOTIMPL;
     }
 
+    /* It is possible for mod_ssl's BIO to be used outside of the
+     * direct control of mod_ssl's input or output filter -- notably,
+     * when mod_ssl initiates a renegotiation.  Switching the BIO mode
+     * back to "blocking" here ensures such operations don't fail with
+     * SSL_ERROR_WANT_READ. */
+    inctx->block = APR_BLOCK_READ;
+
+    /* Handle custom errors. */
     if (status != APR_SUCCESS) {
         return ssl_io_filter_error(f, bb, status);
     }

modules/ssl/ssl_engine_kernel.c

@@ -87,6 +87,29 @@ static apr_status_t upgrade_connection(request_rec *r)
     return APR_SUCCESS;
 }
 
+/* Perform a speculative (and non-blocking) read from the connection
+ * filters for the given request, to determine whether there is any
+ * pending data to read.  Return non-zero if there is, else zero. */
+static int has_buffered_data(request_rec *r) 
+{
+    apr_bucket_brigade *bb;
+    apr_off_t len;
+    apr_status_t rv;
+    int result;
+    
+    bb = apr_brigade_create(r->pool, r->connection->bucket_alloc);
+    
+    rv = ap_get_brigade(r->connection->input_filters, bb, AP_MODE_SPECULATIVE,
+                        APR_NONBLOCK_READ, 1); 
+    result = rv == APR_SUCCESS
+        && apr_brigade_length(bb, 1, &len) == APR_SUCCESS
+        && len > 0;
+    
+    apr_brigade_destroy(bb);
+    
+    return result;
+}
+
 /*
  *  Post Read Request Handler
  */
@@ -724,6 +747,23 @@ int ssl_hook_Access(request_rec *r)
         else {
             request_rec *id = r->main ? r->main : r;
 
+            /* Additional mitigation for CVE-2009-3555: At this point,
+             * before renegotiating, an (entire) request has been read
+             * from the connection.  An attacker may have sent further
+             * data to "prefix" any subsequent request by the victim's
+             * client after the renegotiation; this data may already
+             * have been read and buffered.  Forcing a connection
+             * closure after the response ensures such data will be
+             * discarded.  Legimately pipelined HTTP requests will be
+             * retried anyway with this approach. */
+            if (has_buffered_data(r)) {
+                ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r,
+                              "insecure SSL re-negotiation required, but "
+                              "a pipelined request is present; keepalive "
+                              "disabled");
+                r->connection->keepalive = AP_CONN_CLOSE;
+            }
+
             /* do a full renegotiation */
             ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r,
                           "Performing full renegotiation: "