Detect excessive entities expansion upon replacement

If entities expansion in the XML parser is asked for,
it is possble to craft relatively small input document leading
to excessive on-the-fly content generation.
This patch accounts for those replacement and stop parsing
after a given threshold. it can be bypassed as usual with the
HUGE parser option.

include/libxml/parser.h

@@ -310,6 +310,7 @@ struct _xmlParserCtxt {
     xmlParserNodeInfo *nodeInfoTab;   /* array of nodeInfos */
 
     int                input_id;      /* we need to label inputs */
+    unsigned long      sizeentcopy;   /* volume of entity copy */
 };
 
 /**

parser.c

@@ -122,7 +122,7 @@ xmlCreateEntityParserCtxtInternal(const xmlChar *URL, const xmlChar *ID,
  */
 static int
 xmlParserEntityCheck(xmlParserCtxtPtr ctxt, size_t size,
-                     xmlEntityPtr ent)
+                     xmlEntityPtr ent, size_t replacement)
 {
     size_t consumed = 0;
 
@@ -130,7 +130,24 @@ xmlParserEntityCheck(xmlParserCtxtPtr ctxt, size_t size,
         return (0);
     if (ctxt->lastError.code == XML_ERR_ENTITY_LOOP)
         return (1);
-    if (size != 0) {
+    if (replacement != 0) {
+	if (replacement < XML_MAX_TEXT_LENGTH)
+	    return(0);
+
+        /*
+	 * If the volume of entity copy reaches 10 times the
+	 * amount of parsed data and over the large text threshold
+	 * then that's very likely to be an abuse.
+	 */
+        if (ctxt->input != NULL) {
+	    consumed = ctxt->input->consumed +
+	               (ctxt->input->cur - ctxt->input->base);
+	}
+        consumed += ctxt->sizeentities;
+
+        if (replacement < XML_PARSER_NON_LINEAR * consumed)
+	    return(0);
+    } else if (size != 0) {
         /*
          * Do the check based on the replacement size of the entity
          */
@@ -176,7 +193,6 @@ xmlParserEntityCheck(xmlParserCtxtPtr ctxt, size_t size,
          */
         return (0);
     }
-
     xmlFatalErr(ctxt, XML_ERR_ENTITY_LOOP, NULL);
     return (1);
 }
@@ -2743,7 +2759,7 @@ xmlStringLenDecodeEntities(xmlParserCtxtPtr ctxt, const xmlChar *str, int len,
 		    while (*current != 0) { /* non input consuming loop */
 			buffer[nbchars++] = *current++;
 			if (nbchars + XML_PARSER_BUFFER_SIZE > buffer_size) {
-			    if (xmlParserEntityCheck(ctxt, nbchars, ent))
+			    if (xmlParserEntityCheck(ctxt, nbchars, ent, 0))
 				goto int_error;
 			    growBuffer(buffer, XML_PARSER_BUFFER_SIZE);
 			}
@@ -2785,7 +2801,7 @@ xmlStringLenDecodeEntities(xmlParserCtxtPtr ctxt, const xmlChar *str, int len,
 		    while (*current != 0) { /* non input consuming loop */
 			buffer[nbchars++] = *current++;
 			if (nbchars + XML_PARSER_BUFFER_SIZE > buffer_size) {
-			    if (xmlParserEntityCheck(ctxt, nbchars, ent))
+			    if (xmlParserEntityCheck(ctxt, nbchars, ent, 0))
 			        goto int_error;
 			    growBuffer(buffer, XML_PARSER_BUFFER_SIZE);
 			}
@@ -7203,7 +7219,7 @@ xmlParseReference(xmlParserCtxtPtr ctxt) {
 	    xmlFreeNodeList(list);
 	    return;
 	}
-	if (xmlParserEntityCheck(ctxt, 0, ent)) {
+	if (xmlParserEntityCheck(ctxt, 0, ent, 0)) {
 	    xmlFreeNodeList(list);
 	    return;
 	}
@@ -7360,6 +7376,13 @@ xmlParseReference(xmlParserCtxtPtr ctxt) {
 		(ctxt->parseMode == XML_PARSE_READER)) {
 		xmlNodePtr nw = NULL, cur, firstChild = NULL;
 
+		/*
+		 * We are copying here, make sure there is no abuse
+		 */
+		ctxt->sizeentcopy += ent->length;
+		if (xmlParserEntityCheck(ctxt, 0, ent, ctxt->sizeentcopy))
+		    return;
+
 		/*
 		 * when operating on a reader, the entities definitions
 		 * are always owning the entities subtree.
@@ -7400,6 +7423,14 @@ xmlParseReference(xmlParserCtxtPtr ctxt) {
 	    } else if ((list == NULL) || (ctxt->inputNr > 0)) {
 		xmlNodePtr nw = NULL, cur, next, last,
 			   firstChild = NULL;
+
+		/*
+		 * We are copying here, make sure there is no abuse
+		 */
+		ctxt->sizeentcopy += ent->length;
+		if (xmlParserEntityCheck(ctxt, 0, ent, ctxt->sizeentcopy))
+		    return;
+
 		/*
 		 * Copy the entity child list and make it the new
 		 * entity child list. The goal is to make sure any
@@ -14767,6 +14798,7 @@ xmlCtxtReset(xmlParserCtxtPtr ctxt)
     ctxt->catalogs = NULL;
     ctxt->nbentities = 0;
     ctxt->sizeentities = 0;
+    ctxt->sizeentcopy = 0;
     xmlInitNodeInfoSeq(&ctxt->node_seq);
 
     if (ctxt->attsDefault != NULL) {

parserInternals.c

@@ -1719,6 +1719,8 @@ xmlInitParserCtxt(xmlParserCtxtPtr ctxt)
     ctxt->charset = XML_CHAR_ENCODING_UTF8;
     ctxt->catalogs = NULL;
     ctxt->nbentities = 0;
+    ctxt->sizeentities = 0;
+    ctxt->sizeentcopy = 0;
     ctxt->input_id = 1;
     xmlInitNodeInfoSeq(&ctxt->node_seq);
     return(0);