DO NOT MERGE: Fix XPointer paths beginning with range-to

The old code would invoke the broken xmlXPtrRangeToFunction. range-to
isn't really a function but a special kind of location step. Remove
this function and always handle range-to in the XPath code.

The old xmlXPtrRangeToFunction could also be abused to trigger a
use-after-free error with the potential for remote code execution.

Found with afl-fuzz.

Fixes CVE-2016-5131.

Bug: 36554209
Change-Id: I2bd369290a884c432d16796884d48db6285f8502
(cherry picked from commit e875e1cd1fc92fd2daa57826024125cbd0b195c7)

test/XPath/xptr/vidbase

diff --git a/test/XPath/xptr/vidbase b/test/XPath/xptr/vidbase
index b146383..884b106 100644
--- a/test/XPath/xptr/vidbase
+++ b/test/XPath/xptr/vidbase
@@ -1,2 +1,3 @@
 xpointer(id('chapter1')/p)
 xpointer(id('chapter1')/p[1]/range-to(following-sibling::p[2]))
+xpointer(range-to(id('chapter2')))

xpath.c

diff --git a/xpath.c b/xpath.c
index 751665b..67afbca 100644
--- a/xpath.c
+++ b/xpath.c
@@ -10691,13 +10691,18 @@
 		    lc = 1;
 		    break;
 		} else if ((NXT(len) == '(')) {
-		    /* Note Type or Function */
+		    /* Node Type or Function */
 		    if (xmlXPathIsNodeType(name)) {
 #ifdef DEBUG_STEP
 		        xmlGenericError(xmlGenericErrorContext,
 				"PathExpr: Type search\n");
 #endif
 			lc = 1;
+#ifdef LIBXML_XPTR_ENABLED
+                    } else if (ctxt->xptr &&
+                               xmlStrEqual(name, BAD_CAST "range-to")) {
+                        lc = 1;
+#endif
 		    } else {
 #ifdef DEBUG_STEP
 		        xmlGenericError(xmlGenericErrorContext,

xpointer.c

diff --git a/xpointer.c b/xpointer.c
index e86b445..d8a2e59 100644
--- a/xpointer.c
+++ b/xpointer.c
@@ -1295,8 +1295,6 @@
     ret->here = here;
     ret->origin = origin;
 
-    xmlXPathRegisterFunc(ret, (xmlChar *)"range-to",
-	                 xmlXPtrRangeToFunction);
     xmlXPathRegisterFunc(ret, (xmlChar *)"range",
 	                 xmlXPtrRangeFunction);
     xmlXPathRegisterFunc(ret, (xmlChar *)"range-inside",
@@ -2206,76 +2204,14 @@
  * @nargs:  the number of args
  *
  * Implement the range-to() XPointer function
+ *
+ * Obsolete. range-to is not a real function but a special type of location
+ * step which is handled in xpath.c.
  */
 void
-xmlXPtrRangeToFunction(xmlXPathParserContextPtr ctxt, int nargs) {
-    xmlXPathObjectPtr range;
-    const xmlChar *cur;
-    xmlXPathObjectPtr res, obj;
-    xmlXPathObjectPtr tmp;
-    xmlLocationSetPtr newset = NULL;
-    xmlNodeSetPtr oldset;
-    int i;
-
-    if (ctxt == NULL) return;
-    CHECK_ARITY(1);
-    /*
-     * Save the expression pointer since we will have to evaluate
-     * it multiple times. Initialize the new set.
-     */
-    CHECK_TYPE(XPATH_NODESET);
-    obj = valuePop(ctxt);
-    oldset = obj->nodesetval;
-    ctxt->context->node = NULL;
-
-    cur = ctxt->cur;
-    newset = xmlXPtrLocationSetCreate(NULL);
-
-    for (i = 0; i < oldset->nodeNr; i++) {
-	ctxt->cur = cur;
-
-	/*
-	 * Run the evaluation with a node list made of a single item
-	 * in the nodeset.
-	 */
-	ctxt->context->node = oldset->nodeTab[i];
-	tmp = xmlXPathNewNodeSet(ctxt->context->node);
-	valuePush(ctxt, tmp);
-
-	xmlXPathEvalExpr(ctxt);
-	CHECK_ERROR;
-
-	/*
-	 * The result of the evaluation need to be tested to
-	 * decided whether the filter succeeded or not
-	 */
-	res = valuePop(ctxt);
-	range = xmlXPtrNewRangeNodeObject(oldset->nodeTab[i], res);
-	if (range != NULL) {
-	    xmlXPtrLocationSetAdd(newset, range);
-	}
-
-	/*
-	 * Cleanup
-	 */
-	if (res != NULL)
-	    xmlXPathFreeObject(res);
-	if (ctxt->value == tmp) {
-	    res = valuePop(ctxt);
-	    xmlXPathFreeObject(res);
-	}
-
-	ctxt->context->node = NULL;
-    }
-
-    /*
-     * The result is used as the new evaluation set.
-     */
-    xmlXPathFreeObject(obj);
-    ctxt->context->node = NULL;
-    ctxt->context->contextSize = -1;
-    ctxt->context->proximityPosition = -1;
-    valuePush(ctxt, xmlXPtrWrapLocationSet(newset));
+xmlXPtrRangeToFunction(xmlXPathParserContextPtr ctxt,
+                       int nargs ATTRIBUTE_UNUSED) {
+    XP_ERROR(XPATH_EXPR_ERROR);
 }
 
 /**