[clang][analyzer] Check for label location bindings in DereferenceChecker (llvm#91119)

Resolves llvm#89264

Values should not be stored in addresses of labels, this throws a fatal
error when this happens.

---------

Co-authored-by: Balazs Benics <[email protected]>

Author: Rajveer100

clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp

@@ -31,11 +31,13 @@ class DereferenceChecker
     : public Checker< check::Location,
                       check::Bind,
                       EventDispatcher<ImplicitNullDerefEvent> > {
-  enum DerefKind { NullPointer, UndefinedPointerValue };
+  enum DerefKind { NullPointer, UndefinedPointerValue, AddressOfLabel };
 
   BugType BT_Null{this, "Dereference of null pointer", categories::LogicError};
   BugType BT_Undef{this, "Dereference of undefined pointer value",
                    categories::LogicError};
+  BugType BT_Label{this, "Dereference of the address of a label",
+                   categories::LogicError};
 
   void reportBug(DerefKind K, ProgramStateRef State, const Stmt *S,
                  CheckerContext &C) const;
@@ -167,6 +169,11 @@ void DereferenceChecker::reportBug(DerefKind K, ProgramStateRef State,
     DerefStr1 = " results in an undefined pointer dereference";
     DerefStr2 = " results in a dereference of an undefined pointer value";
     break;
+  case DerefKind::AddressOfLabel:
+    BT = &BT_Label;
+    DerefStr1 = " results in an undefined pointer dereference";
+    DerefStr2 = " results in a dereference of an address of a label";
+    break;
   };
 
   // Generate an error node.
@@ -287,6 +294,12 @@ void DereferenceChecker::checkBind(SVal L, SVal V, const Stmt *S,
   if (V.isUndef())
     return;
 
+  // One should never write to label addresses.
+  if (auto Label = L.getAs<loc::GotoLabel>()) {
+    reportBug(DerefKind::AddressOfLabel, C.getState(), S, C);
+    return;
+  }
+
   const MemRegion *MR = L.getAsRegion();
   const TypedValueRegion *TVR = dyn_cast_or_null<TypedValueRegion>(MR);
   if (!TVR)

clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp

@@ -113,6 +113,9 @@ const Expr *bugreporter::getDerefExpr(const Stmt *S) {
       // Pointer arithmetic: '*(x + 2)' -> 'x') etc.
       if (const Expr *Inner = peelOffPointerArithmetic(B)) {
         E = Inner;
+      } else if (B->isAssignmentOp()) {
+        // Follow LHS of assignments: '*p = 404' -> 'p'.
+        E = B->getLHS();
       } else {
         // Probably more arithmetic can be pattern-matched here,
         // but for now give up.

clang/test/Analysis/gh-issue-89185.c

@@ -1,14 +1,13 @@
-// RUN: %clang_analyze_cc1 -analyzer-checker=core,debug.ExprInspection -verify %s
+// RUN: %clang_analyze_cc1 -analyzer-checker=core,debug.ExprInspection -analyzer-output text -verify %s 
 
-void clang_analyzer_dump(char);
-void clang_analyzer_dump_ptr(char*);
+void clang_analyzer_warnIfReached(void);
 
 // https://github.com/llvm/llvm-project/issues/89185
 void binding_to_label_loc() {
-  char *b = &&MyLabel;
+  char *b = &&MyLabel; // expected-note {{'b' initialized here}}
 MyLabel:
-  *b = 0; // no-crash
-  clang_analyzer_dump_ptr(b); // expected-warning {{&&MyLabel}}
-  clang_analyzer_dump(*b); // expected-warning {{Unknown}}
-  // FIXME: We should never reach here, as storing to a label is invalid.
+  *b = 0;
+  // expected-warning@-1 {{Dereference of the address of a label}}
+  // expected-note@-2    {{Dereference of the address of a label}}
+  clang_analyzer_warnIfReached(); // no-warning: Unreachable due to fatal error.
 }