1 files changed, 281 insertions, 0 deletions
diff --git a/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp b/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp
new file mode 100644
index 000000000000..4ee02230649d
--- /dev/null
+++ b/contrib/llvm/tools/clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp
@@ -0,0 +1,281 @@
+//== NullDerefChecker.cpp - Null dereference checker ------------*- C++ -*--==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines NullDerefChecker, a builtin check in ExprEngine that performs
+// checks for null pointers at loads and stores.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/AST/ExprObjC.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/CheckerManager.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+class DereferenceChecker
+    : public Checker< check::Location,
+                      check::Bind,
+                      EventDispatcher<ImplicitNullDerefEvent> > {
+  mutable std::unique_ptr<BuiltinBug> BT_null;
+  mutable std::unique_ptr<BuiltinBug> BT_undef;
+
+  void reportBug(ProgramStateRef State, const Stmt *S, CheckerContext &C,
+                 bool IsBind = false) const;
+
+public:
+  void checkLocation(SVal location, bool isLoad, const Stmt* S,
+                     CheckerContext &C) const;
+  void checkBind(SVal L, SVal V, const Stmt *S, CheckerContext &C) const;
+
+  static void AddDerefSource(raw_ostream &os,
+                             SmallVectorImpl<SourceRange> &Ranges,
+                             const Expr *Ex, const ProgramState *state,
+                             const LocationContext *LCtx,
+                             bool loadedFrom = false);
+};
+} // end anonymous namespace
+
+void
+DereferenceChecker::AddDerefSource(raw_ostream &os,
+                                   SmallVectorImpl<SourceRange> &Ranges,
+                                   const Expr *Ex,
+                                   const ProgramState *state,
+                                   const LocationContext *LCtx,
+                                   bool loadedFrom) {
+  Ex = Ex->IgnoreParenLValueCasts();
+  switch (Ex->getStmtClass()) {
+    default:
+      break;
+    case Stmt::DeclRefExprClass: {
+      const DeclRefExpr *DR = cast<DeclRefExpr>(Ex);
+      if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
+        os << " (" << (loadedFrom ? "loaded from" : "from")
+           << " variable '" <<  VD->getName() << "')";
+        Ranges.push_back(DR->getSourceRange());
+      }
+      break;
+    }
+    case Stmt::MemberExprClass: {
+      const MemberExpr *ME = cast<MemberExpr>(Ex);
+      os << " (" << (loadedFrom ? "loaded from" : "via")
+         << " field '" << ME->getMemberNameInfo() << "')";
+      SourceLocation L = ME->getMemberLoc();
+      Ranges.push_back(SourceRange(L, L));
+      break;
+    }
+    case Stmt::ObjCIvarRefExprClass: {
+      const ObjCIvarRefExpr *IV = cast<ObjCIvarRefExpr>(Ex);
+      os << " (" << (loadedFrom ? "loaded from" : "via")
+         << " ivar '" << IV->getDecl()->getName() << "')";
+      SourceLocation L = IV->getLocation();
+      Ranges.push_back(SourceRange(L, L));
+      break;
+    }    
+  }
+}
+
+void DereferenceChecker::reportBug(ProgramStateRef State, const Stmt *S,
+                                   CheckerContext &C, bool IsBind) const {
+  // Generate an error node.
+  ExplodedNode *N = C.generateSink(State);
+  if (!N)
+    return;
+
+  // We know that 'location' cannot be non-null.  This is what
+  // we call an "explicit" null dereference.
+  if (!BT_null)
+    BT_null.reset(new BuiltinBug(this, "Dereference of null pointer"));
+
+  SmallString<100> buf;
+  llvm::raw_svector_ostream os(buf);
+
+  SmallVector<SourceRange, 2> Ranges;
+
+  // Walk through lvalue casts to get the original expression
+  // that syntactically caused the load.
+  if (const Expr *expr = dyn_cast<Expr>(S))
+    S = expr->IgnoreParenLValueCasts();
+
+  if (IsBind) {
+    if (const BinaryOperator *BO = dyn_cast<BinaryOperator>(S)) {
+      if (BO->isAssignmentOp())
+        S = BO->getRHS();
+    } else if (const DeclStmt *DS = dyn_cast<DeclStmt>(S)) {
+      assert(DS->isSingleDecl() && "We process decls one by one");
+      if (const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl()))
+        if (const Expr *Init = VD->getAnyInitializer())
+          S = Init;
+    }
+  }
+
+  switch (S->getStmtClass()) {
+  case Stmt::ArraySubscriptExprClass: {
+    os << "Array access";
+    const ArraySubscriptExpr *AE = cast<ArraySubscriptExpr>(S);
+    AddDerefSource(os, Ranges, AE->getBase()->IgnoreParenCasts(),
+                   State.get(), N->getLocationContext());
+    os << " results in a null pointer dereference";
+    break;
+  }
+  case Stmt::UnaryOperatorClass: {
+    os << "Dereference of null pointer";
+    const UnaryOperator *U = cast<UnaryOperator>(S);
+    AddDerefSource(os, Ranges, U->getSubExpr()->IgnoreParens(),
+                   State.get(), N->getLocationContext(), true);
+    break;
+  }
+  case Stmt::MemberExprClass: {
+    const MemberExpr *M = cast<MemberExpr>(S);
+    if (M->isArrow() || bugreporter::isDeclRefExprToReference(M->getBase())) {
+      os << "Access to field '" << M->getMemberNameInfo()
+         << "' results in a dereference of a null pointer";
+      AddDerefSource(os, Ranges, M->getBase()->IgnoreParenCasts(),
+                     State.get(), N->getLocationContext(), true);
+    }
+    break;
+  }
+  case Stmt::ObjCIvarRefExprClass: {
+    const ObjCIvarRefExpr *IV = cast<ObjCIvarRefExpr>(S);
+    os << "Access to instance variable '" << *IV->getDecl()
+       << "' results in a dereference of a null pointer";
+    AddDerefSource(os, Ranges, IV->getBase()->IgnoreParenCasts(),
+                   State.get(), N->getLocationContext(), true);
+    break;
+  }
+  default:
+    break;
+  }
+
+  os.flush();
+  BugReport *report =
+    new BugReport(*BT_null,
+                  buf.empty() ? BT_null->getDescription() : buf.str(),
+                  N);
+
+  bugreporter::trackNullOrUndefValue(N, bugreporter::getDerefExpr(S), *report);
+
+  for (SmallVectorImpl<SourceRange>::iterator
+       I = Ranges.begin(), E = Ranges.end(); I!=E; ++I)
+    report->addRange(*I);
+
+  C.emitReport(report);
+}
+
+void DereferenceChecker::checkLocation(SVal l, bool isLoad, const Stmt* S,
+                                       CheckerContext &C) const {
+  // Check for dereference of an undefined value.
+  if (l.isUndef()) {
+    if (ExplodedNode *N = C.generateSink()) {
+      if (!BT_undef)
+        BT_undef.reset(
+            new BuiltinBug(this, "Dereference of undefined pointer value"));
+
+      BugReport *report =
+        new BugReport(*BT_undef, BT_undef->getDescription(), N);
+      bugreporter::trackNullOrUndefValue(N, bugreporter::getDerefExpr(S),
+                                         *report);
+      C.emitReport(report);
+    }
+    return;
+  }
+
+  DefinedOrUnknownSVal location = l.castAs<DefinedOrUnknownSVal>();
+
+  // Check for null dereferences.
+  if (!location.getAs<Loc>())
+    return;
+
+  ProgramStateRef state = C.getState();
+
+  ProgramStateRef notNullState, nullState;
+  std::tie(notNullState, nullState) = state->assume(location);
+
+  // The explicit NULL case.
+  if (nullState) {
+    if (!notNullState) {
+      reportBug(nullState, S, C);
+      return;
+    }
+
+    // Otherwise, we have the case where the location could either be
+    // null or not-null.  Record the error node as an "implicit" null
+    // dereference.
+    if (ExplodedNode *N = C.generateSink(nullState)) {
+      ImplicitNullDerefEvent event = { l, isLoad, N, &C.getBugReporter() };
+      dispatchEvent(event);
+    }
+  }
+
+  // From this point forward, we know that the location is not null.
+  C.addTransition(notNullState);
+}
+
+void DereferenceChecker::checkBind(SVal L, SVal V, const Stmt *S,
+                                   CheckerContext &C) const {
+  // If we're binding to a reference, check if the value is known to be null.
+  if (V.isUndef())
+    return;
+
+  const MemRegion *MR = L.getAsRegion();
+  const TypedValueRegion *TVR = dyn_cast_or_null<TypedValueRegion>(MR);
+  if (!TVR)
+    return;
+
+  if (!TVR->getValueType()->isReferenceType())
+    return;
+
+  ProgramStateRef State = C.getState();
+
+  ProgramStateRef StNonNull, StNull;
+  std::tie(StNonNull, StNull) = State->assume(V.castAs<DefinedOrUnknownSVal>());
+
+  if (StNull) {
+    if (!StNonNull) {
+      reportBug(StNull, S, C, /*isBind=*/true);
+      return;
+    }
+
+    // At this point the value could be either null or non-null.
+    // Record this as an "implicit" null dereference.
+    if (ExplodedNode *N = C.generateSink(StNull)) {
+      ImplicitNullDerefEvent event = { V, /*isLoad=*/true, N,
+                                       &C.getBugReporter() };
+      dispatchEvent(event);
+    }
+  }
+
+  // Unlike a regular null dereference, initializing a reference with a
+  // dereferenced null pointer does not actually cause a runtime exception in
+  // Clang's implementation of references.
+  //
+  //   int &r = *p; // safe??
+  //   if (p != NULL) return; // uh-oh
+  //   r = 5; // trap here
+  //
+  // The standard says this is invalid as soon as we try to create a "null
+  // reference" (there is no such thing), but turning this into an assumption
+  // that 'p' is never null will not match our actual runtime behavior.
+  // So we do not record this assumption, allowing us to warn on the last line
+  // of this example.
+  //
+  // We do need to add a transition because we may have generated a sink for
+  // the "implicit" null dereference.
+  C.addTransition(State, this);
+}
+
+void ento::registerDereferenceChecker(CheckerManager &mgr) {
+  mgr.registerChecker<DereferenceChecker>();
+}