1 files changed, 190 insertions, 0 deletions
diff --git a/clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
new file mode 100644
index 000000000000..b92757312dc6
--- /dev/null
+++ b/clang/lib/StaticAnalyzer/Checkers/VLASizeChecker.cpp
@@ -0,0 +1,190 @@
+//=== VLASizeChecker.cpp - Undefined dereference checker --------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines VLASizeChecker, a builtin check in ExprEngine that
+// performs checks for declaration of VLA of undefined or zero size.
+// In addition, VLASizeChecker is responsible for defining the extent
+// of the MemRegion that represents a VLA.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Taint.h"
+#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
+#include "clang/AST/CharUnits.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/STLExtras.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace clang;
+using namespace ento;
+using namespace taint;
+
+namespace {
+class VLASizeChecker : public Checker< check::PreStmt<DeclStmt> > {
+  mutable std::unique_ptr<BugType> BT;
+  enum VLASize_Kind { VLA_Garbage, VLA_Zero, VLA_Tainted, VLA_Negative };
+
+  void reportBug(VLASize_Kind Kind, const Expr *SizeE, ProgramStateRef State,
+                 CheckerContext &C,
+                 std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const;
+
+public:
+  void checkPreStmt(const DeclStmt *DS, CheckerContext &C) const;
+};
+} // end anonymous namespace
+
+void VLASizeChecker::reportBug(
+    VLASize_Kind Kind, const Expr *SizeE, ProgramStateRef State,
+    CheckerContext &C, std::unique_ptr<BugReporterVisitor> Visitor) const {
+  // Generate an error node.
+  ExplodedNode *N = C.generateErrorNode(State);
+  if (!N)
+    return;
+
+  if (!BT)
+    BT.reset(new BuiltinBug(
+        this, "Dangerous variable-length array (VLA) declaration"));
+
+  SmallString<256> buf;
+  llvm::raw_svector_ostream os(buf);
+  os << "Declared variable-length array (VLA) ";
+  switch (Kind) {
+  case VLA_Garbage:
+    os << "uses a garbage value as its size";
+    break;
+  case VLA_Zero:
+    os << "has zero size";
+    break;
+  case VLA_Tainted:
+    os << "has tainted size";
+    break;
+  case VLA_Negative:
+    os << "has negative size";
+    break;
+  }
+
+  auto report = std::make_unique<PathSensitiveBugReport>(*BT, os.str(), N);
+  report->addVisitor(std::move(Visitor));
+  report->addRange(SizeE->getSourceRange());
+  bugreporter::trackExpressionValue(N, SizeE, *report);
+  C.emitReport(std::move(report));
+}
+
+void VLASizeChecker::checkPreStmt(const DeclStmt *DS, CheckerContext &C) const {
+  if (!DS->isSingleDecl())
+    return;
+
+  const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
+  if (!VD)
+    return;
+
+  ASTContext &Ctx = C.getASTContext();
+  const VariableArrayType *VLA = Ctx.getAsVariableArrayType(VD->getType());
+  if (!VLA)
+    return;
+
+  // FIXME: Handle multi-dimensional VLAs.
+  const Expr *SE = VLA->getSizeExpr();
+  ProgramStateRef state = C.getState();
+  SVal sizeV = C.getSVal(SE);
+
+  if (sizeV.isUndef()) {
+    reportBug(VLA_Garbage, SE, state, C);
+    return;
+  }
+
+  // See if the size value is known. It can't be undefined because we would have
+  // warned about that already.
+  if (sizeV.isUnknown())
+    return;
+
+  // Check if the size is tainted.
+  if (isTainted(state, sizeV)) {
+    reportBug(VLA_Tainted, SE, nullptr, C,
+              std::make_unique<TaintBugVisitor>(sizeV));
+    return;
+  }
+
+  // Check if the size is zero.
+  DefinedSVal sizeD = sizeV.castAs<DefinedSVal>();
+
+  ProgramStateRef stateNotZero, stateZero;
+  std::tie(stateNotZero, stateZero) = state->assume(sizeD);
+
+  if (stateZero && !stateNotZero) {
+    reportBug(VLA_Zero, SE, stateZero, C);
+    return;
+  }
+
+  // From this point on, assume that the size is not zero.
+  state = stateNotZero;
+
+  // VLASizeChecker is responsible for defining the extent of the array being
+  // declared. We do this by multiplying the array length by the element size,
+  // then matching that with the array region's extent symbol.
+
+  // Check if the size is negative.
+  SValBuilder &svalBuilder = C.getSValBuilder();
+
+  QualType Ty = SE->getType();
+  DefinedOrUnknownSVal Zero = svalBuilder.makeZeroVal(Ty);
+
+  SVal LessThanZeroVal = svalBuilder.evalBinOp(state, BO_LT, sizeD, Zero, Ty);
+  if (Optional<DefinedSVal> LessThanZeroDVal =
+        LessThanZeroVal.getAs<DefinedSVal>()) {
+    ConstraintManager &CM = C.getConstraintManager();
+    ProgramStateRef StatePos, StateNeg;
+
+    std::tie(StateNeg, StatePos) = CM.assumeDual(state, *LessThanZeroDVal);
+    if (StateNeg && !StatePos) {
+      reportBug(VLA_Negative, SE, state, C);
+      return;
+    }
+    state = StatePos;
+  }
+
+  // Convert the array length to size_t.
+  QualType SizeTy = Ctx.getSizeType();
+  NonLoc ArrayLength =
+      svalBuilder.evalCast(sizeD, SizeTy, SE->getType()).castAs<NonLoc>();
+
+  // Get the element size.
+  CharUnits EleSize = Ctx.getTypeSizeInChars(VLA->getElementType());
+  SVal EleSizeVal = svalBuilder.makeIntVal(EleSize.getQuantity(), SizeTy);
+
+  // Multiply the array length by the element size.
+  SVal ArraySizeVal = svalBuilder.evalBinOpNN(
+      state, BO_Mul, ArrayLength, EleSizeVal.castAs<NonLoc>(), SizeTy);
+
+  // Finally, assume that the array's extent matches the given size.
+  const LocationContext *LC = C.getLocationContext();
+  DefinedOrUnknownSVal Extent =
+    state->getRegion(VD, LC)->getExtent(svalBuilder);
+  DefinedOrUnknownSVal ArraySize = ArraySizeVal.castAs<DefinedOrUnknownSVal>();
+  DefinedOrUnknownSVal sizeIsKnown =
+    svalBuilder.evalEQ(state, Extent, ArraySize);
+  state = state->assume(sizeIsKnown, true);
+
+  // Assume should not fail at this point.
+  assert(state);
+
+  // Remember our assumptions!
+  C.addTransition(state);
+}
+
+void ento::registerVLASizeChecker(CheckerManager &mgr) {
+  mgr.registerChecker<VLASizeChecker>();
+}
+
+bool ento::shouldRegisterVLASizeChecker(const LangOptions &LO) {
+  return true;
+}