From 29115868c92c81a4119b05ea95b3c91608a0b6e8 Mon Sep 17 00:00:00 2001
From: Nick Wellnhofer <wellnhofer@aevum.de>
Date: Mon, 30 Jul 2018 12:54:38 +0200
Subject: [PATCH] Fix nullptr deref with XPath logic ops

If the XPath stack is corrupted, for example by a misbehaving extension
function, the "and" and "or" XPath operators could dereference NULL
pointers. Check that the XPath stack isn't empty and optimize the
logic operators slightly.

Closes: https://gitlab.gnome.org/GNOME/libxml2/issues/5

Also see
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=901817
https://bugzilla.redhat.com/show_bug.cgi?id=1595985

This is CVE-2018-14404.

Thanks to Guy Inbar for the report.

CVE: CVE-2018-14404
Upstream-Status: Backport [https://gitlab.gnome.org/GNOME/libxml2/commit/a436374994c47b12d5de1b8b1d191a098fa23594]
Signed-off-by: Sinan Kaya <okaya@kernel.org>
---
 xpath.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/xpath.c b/xpath.c
index 35274731..3fcdc9e1 100644
--- a/xpath.c
+++ b/xpath.c
@@ -13337,9 +13337,8 @@ xmlXPathCompOpEval(xmlXPathParserContextPtr ctxt, xmlXPathStepOpPtr op)
 		return(0);
 	    }
             xmlXPathBooleanFunction(ctxt, 1);
-            arg1 = valuePop(ctxt);
-            arg1->boolval &= arg2->boolval;
-            valuePush(ctxt, arg1);
+            if (ctxt->value != NULL)
+                ctxt->value->boolval &= arg2->boolval;
 	    xmlXPathReleaseObject(ctxt->context, arg2);
             return (total);
         case XPATH_OP_OR:
@@ -13363,9 +13362,8 @@ xmlXPathCompOpEval(xmlXPathParserContextPtr ctxt, xmlXPathStepOpPtr op)
 		return(0);
 	    }
             xmlXPathBooleanFunction(ctxt, 1);
-            arg1 = valuePop(ctxt);
-            arg1->boolval |= arg2->boolval;
-            valuePush(ctxt, arg1);
+            if (ctxt->value != NULL)
+                ctxt->value->boolval |= arg2->boolval;
 	    xmlXPathReleaseObject(ctxt->context, arg2);
             return (total);
         case XPATH_OP_EQUAL:
-- 
2.19.0