From 7f70302bfa9faeac9c9f7be8adf96d32c16acb72 Mon Sep 17 00:00:00 2001
From: Nick Wellnhofer <wellnhofer@aevum.de>
Date: Tue, 8 Feb 2022 03:29:24 +0100
Subject: [PATCH] [CVE-2022-23308] Use-after-free of ID and IDREF attributes

If a document is parsed with XML_PARSE_DTDVALID and without
XML_PARSE_NOENT, the value of ID attributes has to be normalized after
potentially expanding entities in xmlRemoveID. Otherwise, later calls
to xmlGetID can return a pointer to previously freed memory.

ID attributes which are empty or contain only whitespace after
entity expansion are affected in a similar way. This is fixed by
not storing such attributes in the ID table.

The test to detect streaming mode when validating against a DTD was
broken. In connection with the defects above, this could result in a
use-after-free when using the xmlReader interface with validation.
Fix detection of streaming mode to avoid similar issues. (This changes
the expected result of a test case. But as far as I can tell, using the
XML reader with XIncludes referencing the root document never worked
properly, anyway.)

All of these issues can result in denial of service. Using xmlReader
with validation could result in disclosure of memory via the error
channel, typically stderr. The security impact of xmlGetID returning
a pointer to freed memory depends on the application. The typical use
case of calling xmlGetID on an unmodified document is not affected.
---
 valid.c | 88 +++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 55 insertions(+), 33 deletions(-)

diff --git a/valid.c b/valid.c
index a64b96be..5b81059f 100644
--- a/valid.c
+++ b/valid.c
@@ -479,6 +479,35 @@ nodeVPop(xmlValidCtxtPtr ctxt)
     return (ret);
 }
 
+/**
+ * xmlValidNormalizeString:
+ * @str: a string
+ *
+ * Normalize a string in-place.
+ */
+static void
+xmlValidNormalizeString(xmlChar *str) {
+    xmlChar *dst;
+    const xmlChar *src;
+
+    if (str == NULL)
+        return;
+    src = str;
+    dst = str;
+
+    while (*src == 0x20) src++;
+    while (*src != 0) {
+	if (*src == 0x20) {
+	    while (*src == 0x20) src++;
+	    if (*src != 0)
+		*dst++ = 0x20;
+	} else {
+	    *dst++ = *src++;
+	}
+    }
+    *dst = 0;
+}
+
 #ifdef DEBUG_VALID_ALGO
 static void
 xmlValidPrintNode(xmlNodePtr cur) {
@@ -2546,6 +2575,24 @@ xmlDumpNotationTable(xmlBufferPtr buf, xmlNotationTablePtr table) {
 	    (xmlDictOwns(dict, (const xmlChar *)(str)) == 0)))	\
 	    xmlFree((char *)(str));
 
+static int
+xmlIsStreaming(xmlValidCtxtPtr ctxt) {
+    xmlParserCtxtPtr pctxt;
+
+    if (ctxt == NULL)
+        return(0);
+    /*
+     * These magic values are also abused to detect whether we're validating
+     * while parsing a document. In this case, userData points to the parser
+     * context.
+     */
+    if ((ctxt->finishDtd != XML_CTXT_FINISH_DTD_0) &&
+        (ctxt->finishDtd != XML_CTXT_FINISH_DTD_1))
+        return(0);
+    pctxt = ctxt->userData;
+    return(pctxt->parseMode == XML_PARSE_READER);
+}
+
 /**
  * xmlFreeID:
  * @not:  A id
@@ -2589,7 +2636,7 @@ xmlAddID(xmlValidCtxtPtr ctxt, xmlDocPtr doc, const xmlChar *value,
     if (doc == NULL) {
 	return(NULL);
     }
-    if (value == NULL) {
+    if ((value == NULL) || (value[0] == 0)) {
 	return(NULL);
     }
     if (attr == NULL) {
@@ -2620,7 +2667,7 @@ xmlAddID(xmlValidCtxtPtr ctxt, xmlDocPtr doc, const xmlChar *value,
      */
     ret->value = xmlStrdup(value);
     ret->doc = doc;
-    if ((ctxt != NULL) && (ctxt->vstateNr != 0)) {
+    if (xmlIsStreaming(ctxt)) {
 	/*
 	 * Operating in streaming mode, attr is gonna disapear
 	 */
@@ -2754,6 +2801,7 @@ xmlRemoveID(xmlDocPtr doc, xmlAttrPtr attr) {
     ID = xmlNodeListGetString(doc, attr->children, 1);
     if (ID == NULL)
         return(-1);
+    xmlValidNormalizeString(ID);
 
     id = xmlHashLookup(table, ID);
     if (id == NULL || id->attr != attr) {
@@ -2942,7 +2990,7 @@ xmlAddRef(xmlValidCtxtPtr ctxt, xmlDocPtr doc, const xmlChar *value,
      * fill the structure.
      */
     ret->value = xmlStrdup(value);
-    if ((ctxt != NULL) && (ctxt->vstateNr != 0)) {
+    if (xmlIsStreaming(ctxt)) {
 	/*
 	 * Operating in streaming mode, attr is gonna disapear
 	 */
@@ -3962,8 +4010,7 @@ xmlValidateAttributeValue2(xmlValidCtxtPtr ctxt, xmlDocPtr doc,
 xmlChar *
 xmlValidCtxtNormalizeAttributeValue(xmlValidCtxtPtr ctxt, xmlDocPtr doc,
 	     xmlNodePtr elem, const xmlChar *name, const xmlChar *value) {
-    xmlChar *ret, *dst;
-    const xmlChar *src;
+    xmlChar *ret;
     xmlAttributePtr attrDecl = NULL;
     int extsubset = 0;
 
@@ -4004,19 +4051,7 @@ xmlValidCtxtNormalizeAttributeValue(xmlValidCtxtPtr ctxt, xmlDocPtr doc,
     ret = xmlStrdup(value);
     if (ret == NULL)
 	return(NULL);
-    src = value;
-    dst = ret;
-    while (*src == 0x20) src++;
-    while (*src != 0) {
-	if (*src == 0x20) {
-	    while (*src == 0x20) src++;
-	    if (*src != 0)
-		*dst++ = 0x20;
-	} else {
-	    *dst++ = *src++;
-	}
-    }
-    *dst = 0;
+    xmlValidNormalizeString(ret);
     if ((doc->standalone) && (extsubset == 1) && (!xmlStrEqual(value, ret))) {
 	xmlErrValidNode(ctxt, elem, XML_DTD_NOT_STANDALONE,
 "standalone: %s on %s value had to be normalized based on external subset declaration\n",
@@ -4048,8 +4083,7 @@ xmlValidCtxtNormalizeAttributeValue(xmlValidCtxtPtr ctxt, xmlDocPtr doc,
 xmlChar *
 xmlValidNormalizeAttributeValue(xmlDocPtr doc, xmlNodePtr elem,
 			        const xmlChar *name, const xmlChar *value) {
-    xmlChar *ret, *dst;
-    const xmlChar *src;
+    xmlChar *ret;
     xmlAttributePtr attrDecl = NULL;
 
     if (doc == NULL) return(NULL);
@@ -4079,19 +4113,7 @@ xmlValidNormalizeAttributeValue(xmlDocPtr doc, xmlNodePtr elem,
     ret = xmlStrdup(value);
     if (ret == NULL)
 	return(NULL);
-    src = value;
-    dst = ret;
-    while (*src == 0x20) src++;
-    while (*src != 0) {
-	if (*src == 0x20) {
-	    while (*src == 0x20) src++;
-	    if (*src != 0)
-		*dst++ = 0x20;
-	} else {
-	    *dst++ = *src++;
-	}
-    }
-    *dst = 0;
+    xmlValidNormalizeString(ret);
     return(ret);
 }
 
-- 
2.35.1