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Fix memory leak in XMLSERIALIZE(... INDENT).

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xmltotext_with_options sometimes tries to replace the existing
root node of a libxml2 document.  In that case xmlDocSetRootElement
will unlink and return the old root node; if we fail to free it,
it's leaked for the remainder of the session.  The amount of memory
at stake is not large, a couple hundred bytes per occurrence, but
that could still become annoying in heavy usage.

Our only other xmlDocSetRootElement call is not at risk because
it's working on a just-created document, but let's modify that
code too to make it clear that it's dependent on that.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Jim Jones <jim.jones@uni-muenster.de>
Discussion: https://postgr.es/m/1358967.1747858817@sss.pgh.pa.us
Backpatch-through: 16
This commit is contained in:
Tom Lane 2025-05-22 13:52:46 -04:00
parent 0d20635858
commit ee58de1008
1 changed files with 17 additions and 4 deletions
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21
src/backend/utils/adt/xml.c
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@ -733,6 +733,7 @@ xmltotext_with_options(xmltype *data, XmlOptionType xmloption_arg, bool indent)
* content nodes, and then iterate over the nodes.
*/
xmlNodePtr root;
xmlNodePtr oldroot;
xmlNodePtr newline;
root = xmlNewNode(NULL, (const xmlChar *) "content-root");
@ -740,8 +741,14 @@ xmltotext_with_options(xmltype *data, XmlOptionType xmloption_arg, bool indent)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
"could not allocate xml node");
/* This attaches root to doc, so we need not free it separately. */
xmlDocSetRootElement(doc, root);
/*
* This attaches root to doc, so we need not free it separately...
* but instead, we have to free the old root if there was one.
*/
oldroot = xmlDocSetRootElement(doc, root);
if (oldroot != NULL)
xmlFreeNode(oldroot);
xmlAddChildList(root, content_nodes);
/*
@ -1829,6 +1836,7 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
else
{
xmlNodePtr root;
xmlNodePtr oldroot PG_USED_FOR_ASSERTS_ONLY;
/* set up document with empty root node to be the context node */
doc = xmlNewDoc(version);
@ -1847,8 +1855,13 @@ xml_parse(text *data, XmlOptionType xmloption_arg,
if (root == NULL || xmlerrcxt->err_occurred)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
"could not allocate xml node");
/* This attaches root to doc, so we need not free it separately. */
xmlDocSetRootElement(doc, root);
/*
* This attaches root to doc, so we need not free it separately;
* and there can't yet be any old root to free.
*/
oldroot = xmlDocSetRootElement(doc, root);
Assert(oldroot == NULL);
/* allow empty content */
if (*(utf8string + count))