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Python: Add small api enhancements
determined useful during documentation work.
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‎python/change-notes/2021-03-12-small-api-enhancements.md‎

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lgtm,codescanning
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* Make `ParameterNode` extend `LocalSourceNode`, thus making members like `flowsTo` available.
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* Add member predicate `taintFlowsTo` to `LocalSourceNode` facilitating smoother syntax for local taint tracking.
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* Add member `getALocalTaintSource` to `DataFlow::Node` facilitating smoother syntax for local taint tracking.
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* Add predicate `parameterNode` to map from a `Parameter` to a data-flow node.

‎python/ql/src/semmle/python/dataflow/new/internal/DataFlowPublic.qll‎

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@@ -6,6 +6,7 @@ private import python
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private import DataFlowPrivate
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import semmle.python.dataflow.new.TypeTracker
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import Attributes
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import LocalSources
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private import semmle.python.essa.SsaCompute
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/**
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* Gets a local source node from which data may flow to this node in zero or more local steps.
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*/
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LocalSourceNode getALocalSource() { result.flowsTo(this) }
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/**
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* Gets a local source node from which data may flow to this node in zero or more local steps.
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*/
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LocalSourceNode getALocalTaintSource() { result.taintFlowsTo(this) }
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}
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/** A data-flow node corresponding to an SSA variable. */
@@ -215,7 +221,7 @@ ExprNode exprNode(DataFlowExpr e) { result.getNode().getNode() = e }
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* The value of a parameter at function entry, viewed as a node in a data
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* flow graph.
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*/
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class ParameterNode extends CfgNode {
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class ParameterNode extends CfgNode, LocalSourceNode {
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ParameterDefinition def;
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ParameterNode() {
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Parameter getParameter() { result = def.getParameter() }
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}
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/** Gets a node corresponding to parameter `p`. */
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ParameterNode parameterNode(Parameter p) { result.getParameter() = p }
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/** A data flow node that represents a call argument. */
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class ArgumentNode extends Node {
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ArgumentNode() { this = any(DataFlowCall c).getArg(_) }
@@ -467,103 +476,6 @@ class BarrierGuard extends GuardNode {
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}
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}
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/**
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* A data flow node that is a source of local flow. This includes things like
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* - Expressions
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* - Function parameters
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*/
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class LocalSourceNode extends Node {
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LocalSourceNode() {
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not simpleLocalFlowStep+(any(CfgNode n), this) and
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not this instanceof ModuleVariableNode
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or
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this = any(ModuleVariableNode mvn).getARead()
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}
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/** Holds if this `LocalSourceNode` can flow to `nodeTo` in one or more local flow steps. */
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pragma[inline]
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predicate flowsTo(Node nodeTo) { Cached::hasLocalSource(nodeTo, this) }
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/**
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* Gets a reference (read or write) of attribute `attrName` on this node.
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*/
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AttrRef getAnAttributeReference(string attrName) { Cached::namedAttrRef(this, attrName, result) }
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/**
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* Gets a read of attribute `attrName` on this node.
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*/
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AttrRead getAnAttributeRead(string attrName) { result = getAnAttributeReference(attrName) }
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/**
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* Gets a reference (read or write) of any attribute on this node.
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*/
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AttrRef getAnAttributeReference() {
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Cached::namedAttrRef(this, _, result)
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or
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Cached::dynamicAttrRef(this, result)
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}
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/**
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* Gets a read of any attribute on this node.
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*/
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AttrRead getAnAttributeRead() { result = getAnAttributeReference() }
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/**
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* Gets a call to this node.
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*/
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CallCfgNode getACall() { Cached::call(this, result) }
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}
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cached
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private module Cached {
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/**
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* Holds if `source` is a `LocalSourceNode` that can reach `sink` via local flow steps.
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*
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* The slightly backwards parametering ordering is to force correct indexing.
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*/
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cached
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predicate hasLocalSource(Node sink, Node source) {
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// Declaring `source` to be a `SourceNode` currently causes a redundant check in the
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// recursive case, so instead we check it explicitly here.
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source = sink and
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source instanceof LocalSourceNode
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or
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exists(Node mid |
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hasLocalSource(mid, source) and
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simpleLocalFlowStep(mid, sink)
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)
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}
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/**
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* Holds if `base` flows to the base of `ref` and `ref` has attribute name `attr`.
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*/
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cached
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predicate namedAttrRef(LocalSourceNode base, string attr, AttrRef ref) {
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base.flowsTo(ref.getObject()) and
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ref.getAttributeName() = attr
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}
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/**
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* Holds if `base` flows to the base of `ref` and `ref` has no known attribute name.
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*/
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cached
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predicate dynamicAttrRef(LocalSourceNode base, AttrRef ref) {
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base.flowsTo(ref.getObject()) and
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not exists(ref.getAttributeName())
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}
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/**
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* Holds if `func` flows to the callee of `call`.
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*/
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cached
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predicate call(LocalSourceNode func, CallCfgNode call) {
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exists(CfgNode n |
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func.flowsTo(n) and
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n = call.getFunction()
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)
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}
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}
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/**
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* Algebraic datatype for tracking data content associated with values.
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* Content can be collection elements or object attributes.

‎python/ql/src/semmle/python/dataflow/new/internal/LocalSources.qll‎

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/**
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* Provides support for intra-procedural tracking of a customizable
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* set of data flow nodes.
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*
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* Note that unlike `TypeTracker.qll`, this library only performs
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* local tracking within a function.
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*/
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import python
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import DataFlowPublic
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private import DataFlowPrivate
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private import TaintTrackingPublic
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/**
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* A data flow node that is a source of local flow. This includes things like
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* - Expressions
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* - Function parameters
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*/
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class LocalSourceNode extends Node {
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LocalSourceNode() {
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not simpleLocalFlowStep+(any(CfgNode n), this) and
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not this instanceof ModuleVariableNode
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or
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this = any(ModuleVariableNode mvn).getARead()
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}
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/** Holds if this `LocalSourceNode` can flow to `nodeTo` in one or more local flow steps. */
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pragma[inline]
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predicate flowsTo(Node nodeTo) { Cached::hasLocalSource(nodeTo, this) }
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/** Holds if this `LocalSourceNode` can flow to `nodeTo` in one or more local taint steps. */
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pragma[inline]
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predicate taintFlowsTo(Node nodeTo) { Cached::hasLocalTaintSource(nodeTo, this) }
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/**
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* Gets a reference (read or write) of attribute `attrName` on this node.
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*/
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AttrRef getAnAttributeReference(string attrName) { Cached::namedAttrRef(this, attrName, result) }
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/**
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* Gets a read of attribute `attrName` on this node.
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*/
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AttrRead getAnAttributeRead(string attrName) { result = getAnAttributeReference(attrName) }
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/**
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* Gets a reference (read or write) of any attribute on this node.
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*/
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AttrRef getAnAttributeReference() {
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Cached::namedAttrRef(this, _, result)
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or
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Cached::dynamicAttrRef(this, result)
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}
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/**
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* Gets a read of any attribute on this node.
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*/
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AttrRead getAnAttributeRead() { result = getAnAttributeReference() }
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/**
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* Gets a call to this node.
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*/
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CallCfgNode getACall() { Cached::call(this, result) }
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}
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cached
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private module Cached {
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/**
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* Holds if `source` is a `LocalSourceNode` that can reach `sink` via local flow steps.
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*
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* The slightly backwards parametering ordering is to force correct indexing.
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*/
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cached
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predicate hasLocalSource(Node sink, Node source) {
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// Declaring `source` to be a `SourceNode` currently causes a redundant check in the
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// recursive case, so instead we check it explicitly here.
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source = sink and
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source instanceof LocalSourceNode
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or
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exists(Node mid |
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hasLocalSource(mid, source) and
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simpleLocalFlowStep(mid, sink)
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)
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}
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/**
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* Holds if `source` is a `LocalSourceNode` that can reach `sink` via local taint steps.
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*
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* The slightly backwards parametering ordering is to force correct indexing.
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*/
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cached
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predicate hasLocalTaintSource(Node sink, Node source) {
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// Declaring `source` to be a `SourceNode` currently causes a redundant check in the
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// recursive case, so instead we check it explicitly here.
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source = sink and
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source instanceof LocalSourceNode
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or
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exists(Node mid |
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hasLocalTaintSource(mid, source) and
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localTaintStep(mid, sink)
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)
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}
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/**
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* Holds if `base` flows to the base of `ref` and `ref` has attribute name `attr`.
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*/
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cached
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predicate namedAttrRef(LocalSourceNode base, string attr, AttrRef ref) {
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base.flowsTo(ref.getObject()) and
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ref.getAttributeName() = attr
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}
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/**
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* Holds if `base` flows to the base of `ref` and `ref` has no known attribute name.
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*/
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cached
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predicate dynamicAttrRef(LocalSourceNode base, AttrRef ref) {
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base.flowsTo(ref.getObject()) and
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not exists(ref.getAttributeName())
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}
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/**
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* Holds if `func` flows to the callee of `call`.
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*/
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cached
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predicate call(LocalSourceNode func, CallCfgNode call) {
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exists(CfgNode n |
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func.flowsTo(n) and
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n = call.getFunction()
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)
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}
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}

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