[PATCH 2/2] Fix libxml leaks in contrib/xml2 xpath_table

xpath_table() did not release libxml objects allocated while evaluating
XPath expressions.  xmlXPathCompiledEval() returns an xmlXPathObjectPtr
that must be freed, and string results copied into the tuple input array
must be freed after BuildTupleFromCStrings() has consumed them.

Track the current libxml objects across the existing PG_TRY block so they
are also released on error.
---
 contrib/xml2/xpath.c | 47 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/contrib/xml2/xpath.c b/contrib/xml2/xpath.c
index 94819961787..ac140a640e0 100644
--- a/contrib/xml2/xpath.c
+++ b/contrib/xml2/xpath.c
@@ -643,6 +643,10 @@ xpath_table(PG_FUNCTION_ARGS)
 	StringInfoData query_buf;
 	PgXmlErrorContext *xmlerrcxt;
 	volatile xmlDocPtr doctree = NULL;
+	xmlXPathContextPtr volatile ctxt = NULL;
+	xmlXPathObjectPtr volatile res = NULL;
+	xmlXPathCompExprPtr volatile comppath = NULL;
+	xmlChar    *volatile resstr = NULL;
 
 	InitMaterializedSRF(fcinfo, MAT_SRF_USE_EXPECTED_DESC);
 
@@ -662,7 +666,7 @@ xpath_table(PG_FUNCTION_ARGS)
 
 	attinmeta = TupleDescGetAttInMetadata(rsinfo->setDesc);
 
-	values = (char **) palloc(rsinfo->setDesc->natts * sizeof(char *));
+	values = (char **) palloc0(rsinfo->setDesc->natts * sizeof(char *));
 	xpaths = (xmlChar **) palloc(rsinfo->setDesc->natts * sizeof(xmlChar *));
 
 	/*
@@ -732,10 +736,6 @@ xpath_table(PG_FUNCTION_ARGS)
 		{
 			char	   *pkey;
 			char	   *xmldoc;
-			xmlXPathContextPtr ctxt;
-			xmlXPathObjectPtr res;
-			xmlChar    *resstr;
-			xmlXPathCompExprPtr comppath;
 			HeapTuple	ret_tuple;
 
 			/* Extract the row data as C Strings */
@@ -780,6 +780,11 @@ xpath_table(PG_FUNCTION_ARGS)
 					had_values = false;
 					for (j = 0; j < numpaths; j++)
 					{
+						ctxt = NULL;
+						res = NULL;
+						comppath = NULL;
+						resstr = NULL;
+
 						ctxt = xmlXPathNewContext(doctree);
 						if (ctxt == NULL || pg_xml_error_occurred(xmlerrcxt))
 							xml_ereport(xmlerrcxt,
@@ -798,6 +803,7 @@ xpath_table(PG_FUNCTION_ARGS)
 						/* Now evaluate the path expression. */
 						res = xmlXPathCompiledEval(comppath, ctxt);
 						xmlXPathFreeCompExpr(comppath);
+						comppath = NULL;
 
 						if (res != NULL)
 						{
@@ -842,8 +848,16 @@ xpath_table(PG_FUNCTION_ARGS)
 							 * result tuple.
 							 */
 							values[j + 1] = (char *) resstr;
+							resstr = NULL;
+						}
+
+						if (res != NULL)
+						{
+							xmlXPathFreeObject(res);
+							res = NULL;
 						}
 						xmlXPathFreeContext(ctxt);
+						ctxt = NULL;
 					}
 
 					/* Now add the tuple to the output, if there is one. */
@@ -854,6 +868,16 @@ xpath_table(PG_FUNCTION_ARGS)
 						heap_freetuple(ret_tuple);
 					}
 
+					/* BuildTupleFromCStrings() has copied the values. */
+					for (j = 1; j < rsinfo->setDesc->natts; j++)
+					{
+						if (values[j] != NULL)
+						{
+							xmlFree((xmlChar *) values[j]);
+							values[j] = NULL;
+						}
+					}
+
 					rownr++;
 				} while (had_values);
 			}
@@ -870,6 +894,19 @@ xpath_table(PG_FUNCTION_ARGS)
 	}
 	PG_CATCH();
 	{
+		if (resstr != NULL)
+			xmlFree(resstr);
+		for (j = 1; j < rsinfo->setDesc->natts; j++)
+		{
+			if (values[j] != NULL)
+				xmlFree((xmlChar *) values[j]);
+		}
+		if (res != NULL)
+			xmlXPathFreeObject(res);
+		if (comppath != NULL)
+			xmlXPathFreeCompExpr(comppath);
+		if (ctxt != NULL)
+			xmlXPathFreeContext(ctxt);
 		if (doctree != NULL)
 			xmlFreeDoc(doctree);
 
-- 
2.54.0


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