clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp

   1 //=== PointerSubChecker.cpp - Pointer subtraction checker ------*- C++ -*--===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This files defines PointerSubChecker, a builtin checker that checks for
  10 // pointer subtractions on two pointers pointing to different memory chunks.
  11 // This check corresponds to CWE-469.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
  16 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
  17 #include "clang/StaticAnalyzer/Core/Checker.h"
  18 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
  19 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
  20 #include "llvm/ADT/StringRef.h"
  21
  22 using namespace clang;
  23 using namespace ento;
  24
  25 namespace {
  26 class PointerSubChecker
  27   : public Checker< check::PreStmt<BinaryOperator> > {
  28   mutable std::unique_ptr<BugType> BT;
  29
  30 public:
  31   void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
  32 };
  33 }
  34
  35 void PointerSubChecker::checkPreStmt(const BinaryOperator *B,
  36                                      CheckerContext &C) const {
  37   // When doing pointer subtraction, if the two pointers do not point to the
  38   // same memory chunk, emit a warning.
  39   if (B->getOpcode() != BO_Sub)
  40     return;
  41
  42   SVal LV = C.getSVal(B->getLHS());
  43   SVal RV = C.getSVal(B->getRHS());
  44
  45   const MemRegion *LR = LV.getAsRegion();
  46   const MemRegion *RR = RV.getAsRegion();
  47
  48   if (!(LR && RR))
  49     return;
  50
  51   const MemRegion *BaseLR = LR->getBaseRegion();
  52   const MemRegion *BaseRR = RR->getBaseRegion();
  53
  54   if (BaseLR == BaseRR)
  55     return;
  56
  57   // Allow arithmetic on different symbolic regions.
  58   if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR))
  59     return;
  60
  61   if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
  62     if (!BT)
  63       BT.reset(new BugType(this, "Pointer subtraction"));
  64     constexpr llvm::StringLiteral Msg =
  65         "Subtraction of two pointers that do not point to the same memory "
  66         "chunk may cause incorrect result.";
  67     auto R = std::make_unique<PathSensitiveBugReport>(*BT, Msg, N);
  68     R->addRange(B->getSourceRange());
  69     C.emitReport(std::move(R));
  70   }
  71 }
  72
  73 void ento::registerPointerSubChecker(CheckerManager &mgr) {
  74   mgr.registerChecker<PointerSubChecker>();
  75 }
  76
  77 bool ento::shouldRegisterPointerSubChecker(const CheckerManager &mgr) {
  78   return true;
  79 }