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[CVE-2022-40304] Fix dict corruption caused by entity reference cycles

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When an entity reference cycle is detected, the entity content is
cleared by setting its first byte to zero. But the entity content might
be allocated from a dict. In this case, the dict entry becomes corrupted
leading to all kinds of logic errors, including memory errors like
double-frees.

Stop storing entity content, orig, ExternalID and SystemID in a dict.
These values are unlikely to occur multiple times in a document, so they
shouldn't have been stored in a dict in the first place.

Thanks to Ned Williamson and Nathan Wachholz working with Google Project
Zero for the report!
This commit is contained in:
Nick Wellnhofer 2022-08-31 22:11:25 +02:00
parent c846986356
commit 1b41ec4e94
1 changed files with 16 additions and 39 deletions
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55
entities.c
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@ -128,36 +128,19 @@ xmlFreeEntity(xmlEntityPtr entity)
if ((entity->children) && (entity->owner == 1) &&
(entity == (xmlEntityPtr) entity->children->parent))
xmlFreeNodeList(entity->children);
if (dict != NULL) {
if ((entity->name != NULL) && (!xmlDictOwns(dict, entity->name)))
xmlFree((char *) entity->name);
if ((entity->ExternalID != NULL) &&
(!xmlDictOwns(dict, entity->ExternalID)))
xmlFree((char *) entity->ExternalID);
if ((entity->SystemID != NULL) &&
(!xmlDictOwns(dict, entity->SystemID)))
xmlFree((char *) entity->SystemID);
if ((entity->URI != NULL) && (!xmlDictOwns(dict, entity->URI)))
xmlFree((char *) entity->URI);
if ((entity->content != NULL)
&& (!xmlDictOwns(dict, entity->content)))
xmlFree((char *) entity->content);
if ((entity->orig != NULL) && (!xmlDictOwns(dict, entity->orig)))
xmlFree((char *) entity->orig);
} else {
if (entity->name != NULL)
xmlFree((char *) entity->name);
if (entity->ExternalID != NULL)
xmlFree((char *) entity->ExternalID);
if (entity->SystemID != NULL)
xmlFree((char *) entity->SystemID);
if (entity->URI != NULL)
xmlFree((char *) entity->URI);
if (entity->content != NULL)
xmlFree((char *) entity->content);
if (entity->orig != NULL)
xmlFree((char *) entity->orig);
}
if ((entity->name != NULL) &&
((dict == NULL) || (!xmlDictOwns(dict, entity->name))))
xmlFree((char *) entity->name);
if (entity->ExternalID != NULL)
xmlFree((char *) entity->ExternalID);
if (entity->SystemID != NULL)
xmlFree((char *) entity->SystemID);
if (entity->URI != NULL)
xmlFree((char *) entity->URI);
if (entity->content != NULL)
xmlFree((char *) entity->content);
if (entity->orig != NULL)
xmlFree((char *) entity->orig);
xmlFree(entity);
}
@ -193,18 +176,12 @@ xmlCreateEntity(xmlDictPtr dict, const xmlChar *name, int type,
ret->SystemID = xmlStrdup(SystemID);
} else {
ret->name = xmlDictLookup(dict, name, -1);
if (ExternalID != NULL)
ret->ExternalID = xmlDictLookup(dict, ExternalID, -1);
if (SystemID != NULL)
ret->SystemID = xmlDictLookup(dict, SystemID, -1);
ret->ExternalID = xmlStrdup(ExternalID);
ret->SystemID = xmlStrdup(SystemID);
}
if (content != NULL) {
ret->length = xmlStrlen(content);
if ((dict != NULL) && (ret->length < 5))
ret->content = (xmlChar *)
xmlDictLookup(dict, content, ret->length);
else
ret->content = xmlStrndup(content, ret->length);
ret->content = xmlStrndup(content, ret->length);
} else {
ret->length = 0;
ret->content = NULL;