Rust: Flow through enum constructors

Author: hvitved

rust/ql/lib/codeql/rust/dataflow/DataFlow.qll

@@ -19,6 +19,10 @@ module DataFlow {
 
   final class PostUpdateNode = Node::PostUpdateNode;
 
+  final class Content = DataFlowImpl::Content;
+
+  final class ContentSet = DataFlowImpl::ContentSet;
+
   /**
    * Holds if data flows from `nodeFrom` to `nodeTo` in exactly one local
    * (intra-procedural) step.

rust/ql/lib/codeql/rust/dataflow/internal/DataFlowImpl.qll

@@ -115,6 +115,11 @@ module Node {
      */
     ExprCfgNode asExpr() { none() }
 
+    /**
+     * Gets the pattern that corresponds to this node, if any.
+     */
+    PatCfgNode asPat() { none() }
+
     /** Gets the enclosing callable. */
     DataFlowCallable getEnclosingCallable() { result = TCfgScope(this.getCfgScope()) }
 
@@ -177,8 +182,7 @@ module Node {
 
     PatNode() { this = TPatNode(n) }
 
-    /** Gets the `PatCfgNode` in the CFG that this node corresponds to. */
-    PatCfgNode getPat() { result = n }
+    override PatCfgNode asPat() { result = n }
   }
 
   abstract class ParameterNode extends AstCfgFlowNode { }
@@ -333,18 +337,126 @@ module LocalFlow {
     nodeFrom.(Node::AstCfgFlowNode).getCfgNode() =
       nodeTo.(Node::SsaNode).getDefinitionExt().(Ssa::WriteDefinition).getControlFlowNode()
     or
-    nodeFrom.(Node::PositionalParameterNode).getParameter().getPat() =
-      nodeTo.(Node::PatNode).getPat()
+    nodeFrom.(Node::PositionalParameterNode).getParameter().getPat() = nodeTo.asPat()
     or
     SsaFlow::localFlowStep(_, nodeFrom, nodeTo, _)
     or
     exists(AssignmentExprCfgNode a |
       a.getRhs() = nodeFrom.getCfgNode() and
       a.getLhs() = nodeTo.getCfgNode()
     )
+    or
+    exists(MatchExprCfgNode match |
+      nodeFrom.asExpr() = match.getExpr() and
+      nodeTo.asPat() = match.getArmPat(_)
+    )
   }
 }
 
+abstract class Content extends TContent {
+  abstract string toString();
+}
+
+private class VariantContent extends Content, TVariantContent {
+  private CrateOriginOption crate;
+  private string path;
+  private string name;
+
+  VariantContent() { this = TVariantContent(crate, path, name) }
+
+  override string toString() { result = name }
+}
+
+abstract class ContentSet extends TContentSet {
+  /** Gets a textual representation of this element. */
+  abstract string toString();
+
+  /** Gets a content that may be stored into when storing into this set. */
+  abstract Content getAStoreContent();
+
+  /** Gets a content that may be read from when reading from this set. */
+  abstract Content getAReadContent();
+}
+
+private class SingletonContentSet extends ContentSet, TSingletonContentSet {
+  private Content c;
+
+  SingletonContentSet() { this = TSingletonContentSet(c) }
+
+  Content getContent() { result = c }
+
+  override string toString() { result = c.toString() }
+
+  override Content getAStoreContent() { result = c }
+
+  override Content getAReadContent() { result = c }
+}
+
+private import codeql.util.Option
+
+private class CrateOrigin extends string {
+  CrateOrigin() {
+    this = [any(Item i).getCrateOrigin(), any(Resolvable r).getResolvedCrateOrigin()]
+  }
+}
+
+private class CrateOriginOption = Option<CrateOrigin>::Option;
+
+pragma[nomagic]
+private predicate hasExtendedCanonicalPath(Item i, CrateOriginOption crate, string path) {
+  path = i.getExtendedCanonicalPath() and
+  (
+    crate.asSome() = i.getCrateOrigin()
+    or
+    crate.isNone() and
+    not i.hasCrateOrigin()
+  )
+}
+
+pragma[nomagic]
+private predicate resolvesExtendedCanonicalPath(Resolvable r, CrateOriginOption crate, string path) {
+  path = r.getResolvedPath() and
+  (
+    crate.asSome() = r.getResolvedCrateOrigin()
+    or
+    crate.isNone() and
+    not r.hasResolvedCrateOrigin()
+  )
+}
+
+pragma[nomagic]
+private predicate callResolvesExtendedCanonicalPath(
+  CallExprBase call, CrateOriginOption crate, string path
+) {
+  exists(Resolvable r | resolvesExtendedCanonicalPath(r, crate, path) |
+    r = call.(MethodCallExpr)
+    or
+    r = call.(CallExpr).getExpr().(PathExpr).getPath()
+  )
+}
+
+/** Holds if qualified path `p` resolves to variant `c`. */
+private predicate pathResolvesToVariant(Path p, VariantContent c) {
+  exists(CrateOriginOption crate, string path |
+    resolvesExtendedCanonicalPath(p.getQualifier(), crate, path) and
+    c = TVariantContent(crate, path, p.getPart().getNameRef().getText())
+  )
+  or
+  // TODO: Remove once library types are extracted
+  not p.hasQualifier() and
+  c = TVariantContent(_, "crate::std::option::Option", p.getPart().getNameRef().getText())
+}
+
+/** Holds if `ce` constructs an enum value of type `c`. */
+private predicate variantConstructor(CallExpr ce, VariantContent c) {
+  pathResolvesToVariant(ce.getExpr().(PathExpr).getPath(), c)
+}
+
+/** Holds if `p` destructs an enum value of type `c`. */
+private predicate variantDestructor(TupleStructPat p, VariantContent c) {
+  pathResolvesToVariant(p.getPath(), c)
+}
+
 private class DataFlowCallableAlias = DataFlowCallable;
 
 private class ReturnKindAlias = ReturnKind;
@@ -353,6 +465,10 @@ private class DataFlowCallAlias = DataFlowCall;
 
 private class ParameterPositionAlias = ParameterPosition;
 
+private class ContentAlias = Content;
+
+private class ContentSetAlias = ContentSet;
+
 module RustDataFlow implements InputSig<Location> {
   /**
    * An element, viewed as a node in a data flow graph. Either an expression
@@ -399,55 +515,11 @@ module RustDataFlow implements InputSig<Location> {
 
   final class ReturnKind = ReturnKindAlias;
 
-  private import codeql.util.Option
-
-  private class CrateOrigin extends string {
-    CrateOrigin() {
-      this = [any(Item i).getCrateOrigin(), any(Resolvable r).getResolvedCrateOrigin()]
-    }
-  }
-
-  private class CrateOriginOption = Option<CrateOrigin>::Option;
-
-  pragma[nomagic]
-  private predicate hasExtendedCanonicalPath(
-    DataFlowCallable c, CrateOriginOption crate, string path
-  ) {
-    exists(Item i |
-      i = c.asCfgScope() and
-      path = i.getExtendedCanonicalPath()
-    |
-      crate.asSome() = i.getCrateOrigin()
-      or
-      crate.isNone() and
-      not i.hasCrateOrigin()
-    )
-  }
-
-  pragma[nomagic]
-  private predicate resolvesExtendedCanonicalPath(
-    DataFlowCall c, CrateOriginOption crate, string path
-  ) {
-    exists(Resolvable r |
-      path = r.getResolvedPath() and
-      (
-        r = c.asMethodCallExprCfgNode().getExpr()
-        or
-        r = c.asCallExprCfgNode().getExpr().(PathExprCfgNode).getPath()
-      )
-    |
-      crate.asSome() = r.getResolvedCrateOrigin()
-      or
-      crate.isNone() and
-      not r.hasResolvedCrateOrigin()
-    )
-  }
-
   /** Gets a viable implementation of the target of the given `Call`. */
   DataFlowCallable viableCallable(DataFlowCall call) {
     exists(string path, CrateOriginOption crate |
-      hasExtendedCanonicalPath(result, crate, path) and
-      resolvesExtendedCanonicalPath(call, crate, path)
+      hasExtendedCanonicalPath(result.asCfgScope(), crate, path) and
+      callResolvesExtendedCanonicalPath(call.asCallBaseExprCfgNode().getExpr(), crate, path)
     )
   }
 
@@ -469,24 +541,15 @@ module RustDataFlow implements InputSig<Location> {
 
   predicate typeStrongerThan(DataFlowType t1, DataFlowType t2) { none() }
 
-  final class Content = Void;
-
-  predicate forceHighPrecision(Content c) { none() }
-
-  class ContentSet extends TContentSet {
-    /** Gets a textual representation of this element. */
-    string toString() { result = "ContentSet" }
+  class Content = ContentAlias;
 
-    /** Gets a content that may be stored into when storing into this set. */
-    Content getAStoreContent() { none() }
+  class ContentSet = ContentSetAlias;
 
-    /** Gets a content that may be read from when reading from this set. */
-    Content getAReadContent() { none() }
-  }
+  predicate forceHighPrecision(Content c) { none() }
 
-  final class ContentApprox = Void;
+  final class ContentApprox = Content; // todo
 
-  ContentApprox getContentApprox(Content c) { any() }
+  ContentApprox getContentApprox(Content c) { result = c }
 
   class ParameterPosition = ParameterPositionAlias;
 
@@ -519,14 +582,27 @@ module RustDataFlow implements InputSig<Location> {
    * `node1` references an object with a content `c.getAReadContent()` whose
    * value ends up in `node2`.
    */
-  predicate readStep(Node node1, ContentSet c, Node node2) { none() }
+  predicate readStep(Node node1, ContentSet c, Node node2) {
+    node1.asPat() =
+      any(TupleStructPatCfgNode pat |
+        variantDestructor(pat.getPat(), c.(SingletonContentSet).getContent()) and
+        node2.asPat() = pat.getField(0)
+      )
+  }
 
   /**
    * Holds if data can flow from `node1` to `node2` via a store into `c`.  Thus,
    * `node2` references an object with a content `c.getAStoreContent()` that
    * contains the value of `node1`.
    */
-  predicate storeStep(Node node1, ContentSet c, Node node2) { none() }
+  predicate storeStep(Node node1, ContentSet c, Node node2) {
+    // todo: use post-update
+    node2.asExpr() =
+      any(CallExprCfgNode call |
+        variantConstructor(call.getCallExpr(), c.(SingletonContentSet).getContent()) and
+        node1.asExpr() = call.getArgument(0)
+      )
+  }
 
   /**
    * Holds if values stored inside content `c` are cleared at node `n`. For example,
@@ -593,8 +669,6 @@ module RustDataFlow implements InputSig<Location> {
   class DataFlowSecondLevelScope = Void;
 }
 
-final class ContentSet = RustDataFlow::ContentSet;
-
 import MakeImpl<Location, RustDataFlow>
 
 /** A collection of cached types and predicates to be evaluated in the same stage. */
@@ -612,14 +686,6 @@ private module Cached {
   cached
   newtype TDataFlowCall = TCall(CallExprBaseCfgNode c)
 
-  cached
-  newtype TOptionalContentSet =
-    TAnyElementContent() or
-    TAnyContent()
-
-  cached
-  class TContentSet = TAnyElementContent or TAnyContent;
-
   cached
   newtype TDataFlowCallable = TCfgScope(CfgScope scope)
 
@@ -635,6 +701,24 @@ private module Cached {
       i in [0 .. max([any(ParamList l).getNumberOfParams(), any(ArgList l).getNumberOfArgs()]) - 1]
     } or
     TSelfParameterPosition()
+
+  cached
+  newtype TContent =
+    TVariantContent(CrateOriginOption crate, string path, string name) {
+      exists(Enum e |
+        hasExtendedCanonicalPath(e, crate, path) and
+        // s = e.getExtendedCanonicalPath() and
+        name = e.getVariantList().getAVariant().getName().getText()
+      )
+      or
+      // TODO: Remove once library types are extracted
+      crate.isNone() and
+      path = "crate::std::option::Option" and
+      name = ["None", "Some"]
+    }
+
+  cached
+  newtype TContentSet = TSingletonContentSet(Content c)
 }
 
 import Cached