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C++: Never track flow out of an argv argument #3137

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Mar 26, 2020
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C++: Never track flow out of an argv argument #3137

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9 changes: 8 additions & 1 deletion cpp/ql/src/semmle/code/cpp/ir/dataflow/DefaultTaintTracking.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,14 @@ private DataFlow::Node getNodeForSource(Expr source) {
(
result = DataFlow::exprNode(source)
or
result = DataFlow::definitionByReferenceNode(source)
// Some of the sources in `isUserInput` are intended to match the value of
// an expression, while others (those modeled below) are intended to match
// the taint that propagates out of an argument, like the `char *` argument
// to `gets`. It's impossible here to tell which is which, but the "access
// to argv" source is definitely not intended to match an output argument,
// and it causes false positives if we let it.
result = DataFlow::definitionByReferenceNode(source) and
not argv(source.(VariableAccess).getTarget())
)
}

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