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Improve error handling of libxml2 calls in xml.c

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This commit fixes some defects in the backend's xml.c, found upon
inspection of the internals of libxml2:
- xmlEncodeSpecialChars() can fail on malloc(), returning NULL back to
the caller.  xmltext() assumed that this could never happen.  Like other
code paths, a TRY/CATCH block is added there, covering also the fact
that cstring_to_text_with_len() could fail a memory allocation, where
the backend would miss to free the buffer allocated by
xmlEncodeSpecialChars().
- Some libxml2 routines called in xmlelement() can return NULL, like
xmlAddChildList() or xmlTextWriterStartElement().  Dedicated errors are
added for them.
- xml_xmlnodetoxmltype() missed that xmlXPathCastNodeToString() can fail
on an allocation failure.  In this case, the call can just be moved to
the existing TRY/CATCH block.

All these code paths would cause the server to crash.  As this is
unlikely a problem in practice, no backpatch is done.  Jim and I have
caught these defects, not sure who has scored the most.  The contrib
module xml2/ has similar defects, which will be addressed in a separate
change.

Reported-by: Jim Jones <jim.jones@uni-muenster.de>
Reviewed-by: Jim Jones <jim.jones@uni-muenster.de>
Discussion: https://postgr.es/m/aEEingzOta_S_Nu7@paquier.xyz
This commit is contained in:
Michael Paquier
2025-07-01 08:57:05 +09:00
parent 0836683a89
commit 2e94721747
1 changed files with 62 additions and 16 deletions
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74
src/backend/utils/adt/xml.c
View File

@ -529,14 +529,36 @@ xmltext(PG_FUNCTION_ARGS)
#ifdef USE_LIBXML
text *arg = PG_GETARG_TEXT_PP(0);
text *result;
xmlChar *xmlbuf = NULL;
volatile xmlChar *xmlbuf = NULL;
PgXmlErrorContext *xmlerrcxt;
/* Otherwise, we gotta spin up some error handling. */
xmlerrcxt = pg_xml_init(PG_XML_STRICTNESS_ALL);
PG_TRY();
{
xmlbuf = xmlEncodeSpecialChars(NULL, xml_text2xmlChar(arg));
Assert(xmlbuf);
if (xmlbuf == NULL || xmlerrcxt->err_occurred)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
"could not allocate xmlChar");
result = cstring_to_text_with_len((const char *) xmlbuf,
xmlStrlen((const xmlChar *) xmlbuf));
}
PG_CATCH();
{
if (xmlbuf)
xmlFree((xmlChar *) xmlbuf);
pg_xml_done(xmlerrcxt, true);
PG_RE_THROW();
}
PG_END_TRY();
xmlFree((xmlChar *) xmlbuf);
pg_xml_done(xmlerrcxt, false);
result = cstring_to_text_with_len((const char *) xmlbuf, xmlStrlen(xmlbuf));
xmlFree(xmlbuf);
PG_RETURN_XML_P(result);
#else
NO_XML_SUPPORT();
@ -770,7 +792,10 @@ xmltotext_with_options(xmltype *data, XmlOptionType xmloption_arg, bool indent)
if (oldroot != NULL)
xmlFreeNode(oldroot);
xmlAddChildList(root, content_nodes);
if (xmlAddChildList(root, content_nodes) == NULL ||
xmlerrcxt->err_occurred)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
"could not append xml node list");
/*
* We use this node to insert newlines in the dump. Note: in at
@ -931,7 +956,10 @@ xmlelement(XmlExpr *xexpr,
xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
"could not allocate xmlTextWriter");
xmlTextWriterStartElement(writer, (xmlChar *) xexpr->name);
if (xmlTextWriterStartElement(writer, (xmlChar *) xexpr->name) < 0 ||
xmlerrcxt->err_occurred)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
"could not start xml element");
forboth(arg, named_arg_strings, narg, xexpr->arg_names)
{
@ -939,19 +967,30 @@ xmlelement(XmlExpr *xexpr,
char *argname = strVal(lfirst(narg));
if (str)
xmlTextWriterWriteAttribute(writer,
{
if (xmlTextWriterWriteAttribute(writer,
(xmlChar *) argname,
(xmlChar *) str);
(xmlChar *) str) < 0 ||
xmlerrcxt->err_occurred)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
"could not write xml attribute");
}
}
foreach(arg, arg_strings)
{
char *str = (char *) lfirst(arg);
xmlTextWriterWriteRaw(writer, (xmlChar *) str);
if (xmlTextWriterWriteRaw(writer, (xmlChar *) str) < 0 ||
xmlerrcxt->err_occurred)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
"could not write raw xml text");
}
xmlTextWriterEndElement(writer);
if (xmlTextWriterEndElement(writer) < 0 ||
xmlerrcxt->err_occurred)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
"could not end xml element");
/* we MUST do this now to flush data out to the buffer ... */
xmlFreeTextWriter(writer);
@ -4220,20 +4259,27 @@ xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt)
}
else
{
xmlChar *str;
volatile xmlChar *str = NULL;
str = xmlXPathCastNodeToString(cur);
PG_TRY();
{
char *escaped;
str = xmlXPathCastNodeToString(cur);
if (str == NULL || xmlerrcxt->err_occurred)
xml_ereport(xmlerrcxt, ERROR, ERRCODE_OUT_OF_MEMORY,
"could not allocate xmlChar");
/* Here we rely on XML having the same representation as TEXT */
char *escaped = escape_xml((char *) str);
escaped = escape_xml((char *) str);
result = (xmltype *) cstring_to_text(escaped);
pfree(escaped);
}
PG_FINALLY();
{
xmlFree(str);
if (str)
xmlFree((xmlChar *) str);
}
PG_END_TRY();
}