curl_xml plugin: Fix potential dereference of NULL pointer.

I managed to get collectd to segfault in a couple of places while
playing with it a bit. The first is in the curl_xml module when the
XPATH expression doesn't quite match the input. The crash occurs on line
407 when instance_node->nodeTab[0] is dereferenced. At this point, all
members of instance_node are 0, so dereferencing the array isn't a good
idea. This patch fixes the problem, although I'm not sure if this
particular case actually deserves its own error message.

Signed-off-by: Florian Forster <octo@collectd.org>

diff --git a/src/curl_xml.c b/src/curl_xml.c
index da90d7c..c22172a 100644 (file)
--- a/src/curl_xml.c
+++ b/src/curl_xml.c
@@ -365,7 +365,7 @@ static int cx_handle_instance_xpath (xmlXPathContextPtr xpath_ctx, /* {{{ */
     instance_node = instance_node_obj->nodesetval;
     tmp_size = (instance_node) ? instance_node->nodeNr : 0;
 
-    if ( (tmp_size == 0) && (is_table) )
+    if (tmp_size <= 0)
     {
       WARNING ("curl_xml plugin: "
           "relative xpath expression for 'InstanceFrom' \"%s\" doesn't match "