[LifetimeSafety] Detect expiry of loans to trivially destructed types

clang/include/clang/Analysis/Analyses/LifetimeSafety/FactsGenerator.h

@@ -50,7 +50,7 @@ class FactsGenerator : public ConstStmtVisitor<FactsGenerator> {
  void VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *MTE);
 
 private:
- void handleDestructor(const CFGAutomaticObjDtor &DtorOpt);
+ void handleLifetimeEnds(const CFGLifetimeEnds &LifetimeEnds);
 
  void handleGSLPointerConstruction(const CXXConstructExpr *CCE);
 

clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp

@@ -63,9 +63,9 @@ void FactsGenerator::run() {
  const CFGElement &Element = Block->Elements[I];
  if (std::optional<CFGStmt> CS = Element.getAs<CFGStmt>())
  Visit(CS->getStmt());
- else if (std::optional<CFGAutomaticObjDtor> DtorOpt =
- Element.getAs<CFGAutomaticObjDtor>())
- handleDestructor(*DtorOpt);
+ else if (std::optional<CFGLifetimeEnds> LifetimeEnds =
+ Element.getAs<CFGLifetimeEnds>())
+ handleLifetimeEnds(*LifetimeEnds);
  }
  CurrentBlockFacts.append(EscapesInCurrentBlock.begin(),
  EscapesInCurrentBlock.end());
@@ -229,25 +229,19 @@ void FactsGenerator::VisitMaterializeTemporaryExpr(
  killAndFlowOrigin(*MTE, *MTE->getSubExpr());
 }
 
-void FactsGenerator::handleDestructor(const CFGAutomaticObjDtor &DtorOpt) {
- /// TODO: Also handle trivial destructors (e.g., for `int`
- /// variables) which will never have a CFGAutomaticObjDtor node.
+void FactsGenerator::handleLifetimeEnds(const CFGLifetimeEnds &LifetimeEnds) {
  /// TODO: Handle loans to temporaries.
- /// TODO: Consider using clang::CFG::BuildOptions::AddLifetime to reuse the
- /// lifetime ends.
- const VarDecl *DestructedVD = DtorOpt.getVarDecl();
- if (!DestructedVD)
+ const VarDecl *LifetimeEndsVD = LifetimeEnds.getVarDecl();
+ if (!LifetimeEndsVD)
  return;
  // Iterate through all loans to see if any expire.
- /// TODO(opt): Do better than a linear search to find loans associated with
- /// 'DestructedVD'.
- for (const Loan &L : FactMgr.getLoanMgr().getLoans()) {
- const AccessPath &LoanPath = L.Path;
+ for (const auto &Loan : FactMgr.getLoanMgr().getLoans()) {
+ const AccessPath &LoanPath = Loan.Path;
  // Check if the loan is for a stack variable and if that variable
  // is the one being destructed.
- if (LoanPath.D == DestructedVD)
+ if (LoanPath.D == LifetimeEndsVD)
  CurrentBlockFacts.push_back(FactMgr.createFact<ExpireFact>(
- L.ID, DtorOpt.getTriggerStmt()->getEndLoc()));
+ Loan.ID, LifetimeEnds.getTriggerStmt()->getEndLoc()));
  }
 }
 

clang/lib/Sema/AnalysisBasedWarnings.cpp

@@ -2992,6 +2992,9 @@ void clang::sema::AnalysisBasedWarnings::IssueWarnings(
 
  bool EnableLifetimeSafetyAnalysis = S.getLangOpts().EnableLifetimeSafety;
 
+ if (EnableLifetimeSafetyAnalysis)
+ AC.getCFGBuildOptions().AddLifetime = true;
+
  // Force that certain expressions appear as CFGElements in the CFG. This
  // is used to speed up various analyses.
  // FIXME: This isn't the right factoring. This is here for initial

clang/test/Sema/warn-lifetime-safety-dataflow.cpp

@@ -59,6 +59,7 @@ int return_int_val() {
  int x = 10;
 // CHECK: Block B{{[0-9]+}}:
 // CHECK: Issue ([[L_X:[0-9]+]] (Path: x), ToOrigin: {{[0-9]+}} (Expr: DeclRefExpr))
+// CHECK: Expire ([[L_X:[0-9]+]] (Path: x))
  return x;
 }
 // CHECK-NEXT: End of Block
@@ -77,7 +78,6 @@ void loan_expires_cpp() {
 }
 
 
-// FIXME: No expire for Trivial Destructors
 // CHECK-LABEL: Function: loan_expires_trivial
 void loan_expires_trivial() {
  int trivial_obj = 1;
@@ -86,11 +86,29 @@ void loan_expires_trivial() {
 // CHECK: OriginFlow (Dest: [[O_ADDR_TRIVIAL_OBJ:[0-9]+]] (Expr: UnaryOperator), Src: [[O_DRE_TRIVIAL]] (Expr: DeclRefExpr))
  int* pTrivialObj = &trivial_obj;
 // CHECK: OriginFlow (Dest: {{[0-9]+}} (Decl: pTrivialObj), Src: [[O_ADDR_TRIVIAL_OBJ]] (Expr: UnaryOperator))
-// CHECK-NOT: Expire
+// CHECK: Expire ([[L_TRIVIAL_OBJ:[0-9]+]] (Path: trivial_obj))
 // CHECK-NEXT: End of Block
- // FIXME: Add check for Expire once trivial destructors are handled for expiration.
 }
 
+// Trivial Destructors
+// CHECK-LABEL: Function: return_int_pointer
+int* return_int_pointer() {
+ int* ptr;
+// CHECK: Block B{{[0-9]+}}:
+ int x = 1;
+// CHECK: Issue ([[L_X:[0-9]+]] (Path: x), ToOrigin: [[O_DRE_X:[0-9]+]] (Expr: DeclRefExpr))
+// CHECK: OriginFlow (Dest: [[O_ADDR_X:[0-9]+]] (Expr: UnaryOperator), Src: [[O_DRE_X]] (Expr: DeclRefExpr))
+ ptr = &x;
+// CHECK: Use ([[O_PTR:[0-9]+]] (Decl: ptr), Write)
+// CHECK: OriginFlow (Dest: [[O_PTR]] (Decl: ptr), Src: [[O_ADDR_X]] (Expr: UnaryOperator))
+// CHECK: Use ([[O_PTR]] (Decl: ptr), Read)
+// CHECK: OriginFlow (Dest: [[O_RET_VAL:[0-9]+]] (Expr: ImplicitCastExpr), Src: [[O_PTR]] (Decl: ptr))
+// CHECK: Expire ([[L_X]] (Path: x))
+// CHECK: OriginEscapes ([[O_RET_VAL]] (Expr: ImplicitCastExpr))
+ return ptr;
+}
+// CHECK-NEXT: End of Block
+
 // CHECK-LABEL: Function: conditional
 void conditional(bool condition) {
  int a = 5;

clang/test/Sema/warn-lifetime-safety.cpp

@@ -12,6 +12,10 @@ struct [[gsl::Pointer()]] View {
  void use() const;
 };
 
+class TriviallyDestructedClass {
+ View a, b;
+};
+
 //===----------------------------------------------------------------------===//
 // Basic Definite Use-After-Free (-W...permissive)
 // These are cases where the pointer is guaranteed to be dangling at the use site.
@@ -396,6 +400,24 @@ void loan_from_previous_iteration(MyObj safe, bool condition) {
  } // expected-note {{destroyed here}}
 }
 
+void trivial_int_uaf() {
+ int * a;
+ {
+ int b = 1;
+ a = &b; // expected-warning {{object whose reference is captured does not live long enough}}
+ } // expected-note {{destroyed here}}
+ (void)*a; // expected-note {{later used here}}
+}
+
+void trivial_class_uaf() {
+ TriviallyDestructedClass* ptr;
+ {
+ TriviallyDestructedClass s;
+ ptr = &s; // expected-warning {{object whose reference is captured does not live long enough}}
+ } // expected-note {{destroyed here}}
+ (void)ptr; // expected-note {{later used here}}
+}
+
 //===----------------------------------------------------------------------===//
 // Basic Definite Use-After-Return (Return-Stack-Address) (-W...permissive)
 // These are cases where the pointer is guaranteed to be dangling at the use site.
@@ -493,6 +515,43 @@ MyObj& reference_return_of_local() {
  // expected-note@-1 {{returned here}}
 }
 
+int* trivial_int_uar() {
+ int *a;
+ int b = 1;
+ a = &b; // expected-warning {{address of stack memory is returned later}}
+ return a; // expected-note {{returned here}}
+}
+
+TriviallyDestructedClass* trivial_class_uar () {
+ TriviallyDestructedClass *ptr;
+ TriviallyDestructedClass s;
+ ptr = &s; // expected-warning {{address of stack memory is returned later}}
+ return ptr; // expected-note {{returned here}}
+}
+
+// FIXME: No lifetime warning for this as no expire facts are generated for parameters
+const int& return_parameter(int a) { 
+ return a; 
+}
+
+// FIXME: No lifetime warning for this as no expire facts are generated for parameters
+int* return_pointer_to_parameter(int a) {
+ return &a;
+}
+
+const int& return_reference_to_parameter(int a)
+{
+ const int &b = a; 
+ return b; // expected-warning {{address of stack memory is returned later}}
+ // expected-note@-1 {{returned here}}
+}
+
+const int& get_ref_to_local() {
+ int a = 42;
+ return a; // expected-warning {{address of stack memory is returned later}}
+ // expected-note@-1 {{returned here}}
+}
+
 //===----------------------------------------------------------------------===//
 // Use-After-Scope & Use-After-Return (Return-Stack-Address) Combined
 // These are cases where the diagnostic kind is determined by location
@@ -688,7 +747,8 @@ void lifetimebound_partial_safety(bool cond) {
  v.use(); // expected-note {{later used here}}
 }
 
-// FIXME: Creating reference from lifetimebound call doesn't propagate loans.
+// FIXME: Warning should be on the 'GetObject' call, not the assignment to 'ptr'. 
+// The loan from the lifetimebound argument is not propagated to the call expression itself.
 const MyObj& GetObject(View v [[clang::lifetimebound]]);
 void lifetimebound_return_reference() {
  View v;
@@ -697,9 +757,9 @@ void lifetimebound_return_reference() {
  MyObj obj;
  View temp_v = obj;
  const MyObj& ref = GetObject(temp_v);
- ptr = &ref;
- }
- (void)*ptr;
+ ptr = &ref; // expected-warning {{object whose reference is captured does not live long enough}}
+ } // expected-note {{destroyed here}}
+ (void)*ptr; // expected-note {{later used here}}
 }
 
 // FIXME: No warning for non gsl::Pointer types. Origin tracking is only supported for pointer types.

clang/unittests/Analysis/LifetimeSafetyTest.cpp

@@ -59,6 +59,7 @@ class LifetimeTestRunner {
  BuildOptions.setAllAlwaysAdd();
  BuildOptions.AddImplicitDtors = true;
  BuildOptions.AddTemporaryDtors = true;
+ BuildOptions.AddLifetime = true;
 
  // Run the main analysis.
  Analysis = std::make_unique<LifetimeSafetyAnalysis>(*AnalysisCtx, nullptr);
@@ -1307,6 +1308,42 @@ TEST_F(LifetimeAnalysisTest, LivenessOutsideLoop) {
  EXPECT_THAT(Origins({"p"}), MaybeLiveAt("p1"));
 }
 
+TEST_F(LifetimeAnalysisTest, TrivialDestructorsUAF) {
+ SetupTest(R"(
+ void target() {
+ int *ptr;
+ {
+ int s = 1;
+ ptr = &s;
+ }
+ POINT(p1); 
+ (void)*ptr;
+ }
+ )");
+ EXPECT_THAT(Origin("ptr"), HasLoansTo({"s"}, "p1"));
+ EXPECT_THAT(Origins({"ptr"}), MustBeLiveAt("p1"));
+}
+
+TEST_F(LifetimeAnalysisTest, TrivialClassDestructorsUAF) {
+ SetupTest(R"(
+ class S {
+ View a, b;
+ };
+
+ void target() {
+ S* ptr;
+ {
+ S s;
+ ptr = &s;
+ }
+ POINT(p1);
+ (void)ptr;
+ }
+ )");
+ EXPECT_THAT(Origin("ptr"), HasLoansTo({"s"}, "p1"));
+ EXPECT_THAT(Origins({"ptr"}), MustBeLiveAt("p1"));
+}
+
 TEST_F(LifetimeAnalysisTest, SimpleReturnStackAddress) {
  SetupTest(R"(
  MyObj* target() {
@@ -1506,5 +1543,34 @@ TEST_F(LifetimeAnalysisTest, ReturnBeforeUseAfterScope) {
  EXPECT_THAT(Origins({"p"}), MustBeLiveAt("p1"));
 }
 
+TEST_F(LifetimeAnalysisTest, TrivialDestructorsUAR) {
+ SetupTest(R"(
+ int* target() {
+ int s = 10;
+ int* p = &s;
+ POINT(p1);
+ return p;
+ }
+ )");
+ EXPECT_THAT("s", HasLiveLoanAtExpiry("p1"));
+}
+
+TEST_F(LifetimeAnalysisTest, TrivialClassDestructorsUAR) {
+ SetupTest(R"(
+ class S {
+ View a, b;
+ };
+
+ S* target() {
+ S *ptr;
+ S s;
+ ptr = &s;
+ POINT(p1);
+ return ptr;
+ }
+ )");
+ EXPECT_THAT("s", HasLiveLoanAtExpiry("p1"));
+}
+
 } // anonymous namespace
 } // namespace clang::lifetimes::internal