1 //=== PointerSubChecker.cpp - Pointer subtraction checker ------*- C++ -*--===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This files defines PointerSubChecker, a builtin checker that checks for 11 // pointer subtractions on two pointers pointing to different memory chunks. 12 // This check corresponds to CWE-469. 13 // 14 //===----------------------------------------------------------------------===// 15 16 #include "ClangSACheckers.h" 17 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 18 #include "clang/StaticAnalyzer/Core/Checker.h" 19 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 20 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.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<BuiltinBug> 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 ProgramStateRef state = C.getState(); 43 const LocationContext *LCtx = C.getLocationContext(); 44 SVal LV = state->getSVal(B->getLHS(), LCtx); 45 SVal RV = state->getSVal(B->getRHS(), LCtx); 46 47 const MemRegion *LR = LV.getAsRegion(); 48 const MemRegion *RR = RV.getAsRegion(); 49 50 if (!(LR && RR)) 51 return; 52 53 const MemRegion *BaseLR = LR->getBaseRegion(); 54 const MemRegion *BaseRR = RR->getBaseRegion(); 55 56 if (BaseLR == BaseRR) 57 return; 58 59 // Allow arithmetic on different symbolic regions. 60 if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR)) 61 return; 62 63 if (ExplodedNode *N = C.generateNonFatalErrorNode()) { 64 if (!BT) 65 BT.reset( 66 new BuiltinBug(this, "Pointer subtraction", 67 "Subtraction of two pointers that do not point to " 68 "the same memory chunk may cause incorrect result.")); 69 auto R = llvm::make_unique<BugReport>(*BT, BT->getDescription(), N); 70 R->addRange(B->getSourceRange()); 71 C.emitReport(std::move(R)); 72 } 73 } 74 75 void ento::registerPointerSubChecker(CheckerManager &mgr) { 76 mgr.registerChecker<PointerSubChecker>(); 77 } 78
