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From a8fa5f7b5c3c745397b3178405d6be9fdb3cfcbc Mon Sep 17 00:00:00 2001
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From: Nick Wellnhofer <wellnhofer@aevum.de>
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Date: Wed, 31 Aug 2022 22:11:25 +0200
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Subject: [PATCH 2/2] Fix dict corruption caused by entity reference cycles
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When an entity reference cycle is detected, the entity content is
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cleared by setting its first byte to zero. But the entity content might
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be allocated from a dict. In this case, the dict entry becomes corrupted
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leading to all kinds of logic errors, including memory errors like
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double-frees.
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Stop storing entity content, orig, ExternalID and SystemID in a dict.
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These values are unlikely to occur multiple times in a document, so they
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shouldn't have been stored in a dict in the first place.
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Thanks to Ned Williamson and Nathan Wachholz working with Google Project
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Zero for the report!
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---
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entities.c | 55 ++++++++++++++++--------------------------------------
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1 file changed, 16 insertions(+), 39 deletions(-)
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diff --git a/entities.c b/entities.c
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index c8193376..3bf1c3ce 100644
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--- a/entities.c
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+++ b/entities.c
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@@ -112,36 +112,19 @@ xmlFreeEntity(xmlEntityPtr entity)
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if ((entity->children) && (entity->owner == 1) &&
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(entity == (xmlEntityPtr) entity->children->parent))
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xmlFreeNodeList(entity->children);
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- if (dict != NULL) {
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- if ((entity->name != NULL) && (!xmlDictOwns(dict, entity->name)))
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- xmlFree((char *) entity->name);
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- if ((entity->ExternalID != NULL) &&
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- (!xmlDictOwns(dict, entity->ExternalID)))
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- xmlFree((char *) entity->ExternalID);
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- if ((entity->SystemID != NULL) &&
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- (!xmlDictOwns(dict, entity->SystemID)))
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- xmlFree((char *) entity->SystemID);
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- if ((entity->URI != NULL) && (!xmlDictOwns(dict, entity->URI)))
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- xmlFree((char *) entity->URI);
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- if ((entity->content != NULL)
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- && (!xmlDictOwns(dict, entity->content)))
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- xmlFree((char *) entity->content);
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- if ((entity->orig != NULL) && (!xmlDictOwns(dict, entity->orig)))
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- xmlFree((char *) entity->orig);
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- } else {
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- if (entity->name != NULL)
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- xmlFree((char *) entity->name);
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- if (entity->ExternalID != NULL)
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- xmlFree((char *) entity->ExternalID);
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- if (entity->SystemID != NULL)
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- xmlFree((char *) entity->SystemID);
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- if (entity->URI != NULL)
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- xmlFree((char *) entity->URI);
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- if (entity->content != NULL)
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- xmlFree((char *) entity->content);
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- if (entity->orig != NULL)
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- xmlFree((char *) entity->orig);
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- }
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+ if ((entity->name != NULL) &&
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+ ((dict == NULL) || (!xmlDictOwns(dict, entity->name))))
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+ xmlFree((char *) entity->name);
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+ if (entity->ExternalID != NULL)
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+ xmlFree((char *) entity->ExternalID);
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+ if (entity->SystemID != NULL)
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+ xmlFree((char *) entity->SystemID);
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+ if (entity->URI != NULL)
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+ xmlFree((char *) entity->URI);
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+ if (entity->content != NULL)
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+ xmlFree((char *) entity->content);
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+ if (entity->orig != NULL)
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+ xmlFree((char *) entity->orig);
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xmlFree(entity);
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}
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@@ -177,18 +160,12 @@ xmlCreateEntity(xmlDictPtr dict, const xmlChar *name, int type,
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ret->SystemID = xmlStrdup(SystemID);
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} else {
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ret->name = xmlDictLookup(dict, name, -1);
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- if (ExternalID != NULL)
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- ret->ExternalID = xmlDictLookup(dict, ExternalID, -1);
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- if (SystemID != NULL)
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- ret->SystemID = xmlDictLookup(dict, SystemID, -1);
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+ ret->ExternalID = xmlStrdup(ExternalID);
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+ ret->SystemID = xmlStrdup(SystemID);
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}
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if (content != NULL) {
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ret->length = xmlStrlen(content);
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- if ((dict != NULL) && (ret->length < 5))
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- ret->content = (xmlChar *)
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- xmlDictLookup(dict, content, ret->length);
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- else
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- ret->content = xmlStrndup(content, ret->length);
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+ ret->content = xmlStrndup(content, ret->length);
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} else {
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ret->length = 0;
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ret->content = NULL;
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--
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2.39.0
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