From a436374994c47b12d5de1b8b1d191a098fa23594 Mon Sep 17 00:00:00 2001 From: Nick Wellnhofer 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. --- xpath.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/xpath.c b/xpath.c index 3fae0bf4..5e3bb9ff 100644 --- a/xpath.c +++ b/xpath.c @@ -13234,9 +13234,8 @@ 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: @@ -13252,9 +13251,8 @@ 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: -- 2.22.0