[libxml2] [CVE-2022-23308] Use-after-free of ID and IDREF attributes

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 652dd12a858989b14eed4e84e453059cd3ba340e
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Tue Feb 8 03:29:24 2022 +0100

    [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.

 result/XInclude/ns1.xml.rdr |  2 +-
 valid.c                     | 88 ++++++++++++++++++++++++++++-----------------
 2 files changed, 56 insertions(+), 34 deletions(-)
---
diff --git a/result/XInclude/ns1.xml.rdr b/result/XInclude/ns1.xml.rdr
index f23702f5..9a3a5e76 100644
--- a/result/XInclude/ns1.xml.rdr
+++ b/result/XInclude/ns1.xml.rdr
@@ -1,7 +1,7 @@
 0 1 doc 0 0
 1 14 #text 0 1 
     
-1 1 ns:elem 1 0
+1 1 xi:include 1 0
 1 14 #text 0 1 
     
 1 1 elem 0 0
diff --git a/valid.c b/valid.c
index 5ee391c0..8e596f1d 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) {
@@ -2607,6 +2636,24 @@ 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
@@ -2650,7 +2697,7 @@ 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) {
@@ -2681,7 +2728,7 @@ 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 disappear
         */
@@ -2820,6 +2867,7 @@ 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) {
@@ -3009,7 +3057,7 @@ 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 disappear
         */
@@ -4028,8 +4076,7 @@ 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;
 
@@ -4070,19 +4117,7 @@ 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",
@@ -4114,8 +4149,7 @@ 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);
@@ -4145,19 +4179,7 @@ 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);
 }