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

2025年5月22日 17:52:46 +0000 (13:52 -0400)

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

src/backend/utils/adt/xml.c patch | blob | blame | history

diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c

index db8d0d6a7e8724ca35a069e826220673e6737b61..a4150bff2eaea8f560e48ecf495d2c46d40d5526 100644 (file)

--- a/src/backend/utils/adt/xml.c

+++ b/src/backend/utils/adt/xml.c

@@ -754,6 +754,7 @@ 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");

@@ -761,8 +762,14 @@ 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);

@@ -1850,6 +1857,7 @@ 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);

@@ -1868,8 +1876,13 @@ 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))

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