CVE-2015-7995: Medium severity iphone os vulnerability

A vulnerability in function xsltStylePreCompute" in preproc.c was found, the cause of which is a type confusion leading to DoS.

As reported in https://bugzilla.redhat.com/showbug.cgi?id=1257058 :

""" Through analysis we get to know that parent->ns->href in line 2250 of preproc.c is an invalid value with our poc. The whole process is as follow: 1> The main function in xsltproc.c will call xmlReadFile to read a .xml file. xmlReadFile will return a xmlDocPtr which points to the xmlDoc. When we print xmlDocPtr->children->parent->ns, its value is 0xffffffff. Obviously, this value is not a correct one. 2> Later in xsltStylePreCompute of preproc.c, the function will see whether current element is 'attribute', if yes,if inst->parent!=NULL and parent->ns!=NULL, then it will call xmlStrEqual, the first parameter is a ptr but its value is 0xffffffff! 3> We went further into libxml and see why this happened.The result is : in SAX2.c +2293 of libxml, we found that the first parameter "ctxt->myDoc" is a xmlDocPtr, but it will be teated as a xmlNodePtr. Obviously, xmlDoc and xmlNode have different structure. This is why "xmlDocPtr->children->parent->ns" get a invalid value(0xffffffff), this value comes from xmlDoc->compression. """