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parser: Acknowledge that entities with namespaces are broken

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Entities which reference out-of-scope namespace have always been broken.
xmlParseBalancedChunkMemoryInternal tried to reuse the namespaces
currently in scope but these namespaces were ignored by the SAX handler.
Besides, there could be different namespaces in scope when expanding the
entity again. For example:

    <!DOCTYPE doc [
      <!ENTITY ent "<ns:elem/>">
    ]>
    <doc>
      <decl1 xmlns:ns="urn:ns1">
        &ent;
      </decl1>
      <decl2 xmlns:ns="urn:ns2">
        &ent;
      </decl2>
    </doc>

Add some comments outlining possible solutions to this problem.

For now, we stop copying namespaces to the temporary parser context
in xmlParseBalancedChunkMemoryInternal. This has never really worked
and the recent changes contained a partial fix which uncovered other
problems like a use-after-free with the XML Reader interface, found
by OSS-Fuzz.
This commit is contained in:
Nick Wellnhofer 2023-10-05 17:11:24 +02:00
parent b8e03e13ed
commit 97e99f4112
2 changed files with 69 additions and 22 deletions
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82
parser.c
View File

@ -7267,6 +7267,39 @@ xmlParseReference(xmlParserCtxtPtr ctxt) {
* of validating, or substituting entities were given. Doing so is
* far more secure as the parser will only process data coming from
* the document entity by default.
*
* FIXME: This doesn't work correctly since entities can be
* expanded with different namespace declarations in scope.
* For example:
*
* <!DOCTYPE doc [
* <!ENTITY ent "<ns:elem/>">
* ]>
* <doc>
* <decl1 xmlns:ns="urn:ns1">
* &ent;
* </decl1>
* <decl2 xmlns:ns="urn:ns2">
* &ent;
* </decl2>
* </doc>
*
* Proposed fix:
*
* - Remove the ent->owner optimization which tries to avoid the
* initial copy of the entity. Always make entities own the
* subtree.
* - Ignore current namespace declarations when parsing the
* entity. If a prefix can't be resolved, don't report an error
* but mark it as unresolved.
* - Try to resolve these prefixes when expanding the entity.
* This will require a specialized version of xmlStaticCopyNode
* which can also make use of the namespace hash table to avoid
* quadratic behavior.
*
* Alternatively, we could simply reparse the entity on each
* expansion like we already do with custom SAX callbacks.
* External entity content should be cached in this case.
*/
if (((ent->flags & XML_ENT_PARSED) == 0) &&
((ent->etype != XML_EXTERNAL_GENERAL_PARSED_ENTITY) ||
@ -12876,7 +12909,9 @@ xmlParseBalancedChunkMemoryInternal(xmlParserCtxtPtr oldctxt,
xmlNodePtr content = NULL;
xmlNodePtr last = NULL;
xmlParserErrors ret = XML_ERR_OK;
#if 0
unsigned i;
#endif
if (((oldctxt->depth > 40) && ((oldctxt->options & XML_PARSE_HUGE) == 0)) ||
(oldctxt->depth > 100)) {
@ -12906,29 +12941,38 @@ xmlParseBalancedChunkMemoryInternal(xmlParserCtxtPtr oldctxt,
ctxt->str_xmlns = xmlDictLookup(ctxt->dict, BAD_CAST "xmlns", 5);
ctxt->str_xml_ns = xmlDictLookup(ctxt->dict, XML_XML_NAMESPACE, 36);
/* propagate namespaces down the entity */
if (oldctxt->nsdb != NULL) {
for (i = 0; i < oldctxt->nsdb->hashSize; i++) {
xmlParserNsBucket *bucket = &oldctxt->nsdb->hash[i];
xmlHashedString hprefix, huri;
const xmlChar **ns;
xmlParserNsExtra *extra;
unsigned nsIndex;
/*
* Propagate namespaces down the entity
*
* This is disabled for now. The pre-2.12 code was already broken
* since the SAX handler was using xmlSearchNs which didn't see the
* namespaces added here.
*
* Making entities and namespaces work correctly requires additional
* changes, see xmlParseReference.
*/
#if 0
for (i = 0; i < oldctxt->nsdb->hashSize; i++) {
xmlParserNsBucket *bucket = &oldctxt->nsdb->hash[i];
xmlHashedString hprefix, huri;
const xmlChar **ns;
xmlParserNsExtra *extra;
unsigned nsIndex;
if ((bucket->hashValue != 0) &&
(bucket->index != INT_MAX)) {
nsIndex = bucket->index;
ns = &oldctxt->nsTab[nsIndex * 2];
extra = &oldctxt->nsdb->extra[nsIndex];
if ((bucket->hashValue != 0) &&
(bucket->index != INT_MAX)) {
nsIndex = bucket->index;
ns = &oldctxt->nsTab[nsIndex * 2];
extra = &oldctxt->nsdb->extra[nsIndex];
hprefix.name = ns[0];
hprefix.hashValue = bucket->hashValue;
huri.name = ns[1];
huri.hashValue = extra->uriHashValue;
xmlParserNsPush(ctxt, &hprefix, &huri, extra->saxData, 0);
}
hprefix.name = ns[0];
hprefix.hashValue = bucket->hashValue;
huri.name = ns[1];
huri.hashValue = extra->uriHashValue;
xmlParserNsPush(ctxt, &hprefix, &huri, extra->saxData, 0);
}
}
#endif
oldsax = ctxt->sax;
ctxt->sax = oldctxt->sax;

9
tree.c
View File

@ -4206,7 +4206,10 @@ xmlStaticCopyNode(xmlNodePtr node, xmlDocPtr doc, xmlNodePtr parent,
/*
* Humm, we are copying an element whose namespace is defined
* out of the new tree scope. Search it in the original tree
* and add it at the top of the new tree
* and add it at the top of the new tree.
*
* TODO: Searching the original tree seems unnecessary. We
* already have a namespace URI.
*/
ns = xmlSearchNs(node->doc, node, node->ns->prefix);
if (ns != NULL) {
@ -4214,8 +4217,8 @@ xmlStaticCopyNode(xmlNodePtr node, xmlDocPtr doc, xmlNodePtr parent,
while (root->parent != NULL) root = root->parent;
ret->ns = xmlNewNs(root, ns->href, ns->prefix);
} else {
ret->ns = xmlNewReconciledNs(doc, ret, node->ns);
} else {
ret->ns = xmlNewReconciledNs(doc, ret, node->ns);
}
} else {
/*