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Fix nullptr deref with XPath logic ops

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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.
This commit is contained in:
Nick Wellnhofer 2018-07-30 12:54:38 +02:00
parent b7c50b8dde
commit a436374994
1 changed files with 4 additions and 6 deletions
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10
xpath.c
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@ -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: