Created attachment 1067176 [details]
corrupt xml file

Description of problem:


Version-Release number of selected component (if applicable):
1.1.28

How reproducible:
./xsltproc poc


Actual results:
Denial of Service

Expected results:


Additional info:

Function "xsltStylePreCompute" in preproc.c may cause a denial of service, the root cause is a type confusion.
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.

Possible Patch:
Add a judgement in preproc.c+2248, before call xmlStrEqual we must determine whether parent->type equals XML_DOCUMENT_NODE