1 //== ReturnPointerRangeChecker.cpp ------------------------------*- 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 file defines ReturnPointerRangeChecker, which is a path-sensitive check 10 // which looks for an out-of-bound pointer being returned to callers. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 15 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporterVisitors.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 "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h" 21 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h" 22 23 using namespace clang; 24 using namespace ento; 25 26 namespace { 27 class ReturnPointerRangeChecker : 28 public Checker< check::PreStmt<ReturnStmt> > { 29 mutable std::unique_ptr<BuiltinBug> BT; 30 31 public: 32 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const; 33 }; 34 } 35 36 void ReturnPointerRangeChecker::checkPreStmt(const ReturnStmt *RS, 37 CheckerContext &C) const { 38 ProgramStateRef state = C.getState(); 39 40 const Expr *RetE = RS->getRetValue(); 41 if (!RetE) 42 return; 43 44 SVal V = C.getSVal(RetE); 45 const MemRegion *R = V.getAsRegion(); 46 47 const ElementRegion *ER = dyn_cast_or_null<ElementRegion>(R); 48 if (!ER) 49 return; 50 51 DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>(); 52 // Zero index is always in bound, this also passes ElementRegions created for 53 // pointer casts. 54 if (Idx.isZeroConstant()) 55 return; 56 57 // FIXME: All of this out-of-bounds checking should eventually be refactored 58 // into a common place. 59 DefinedOrUnknownSVal ElementCount = getDynamicElementCount( 60 state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType()); 61 62 // We assume that the location after the last element in the array is used as 63 // end() iterator. Reporting on these would return too many false positives. 64 if (Idx == ElementCount) 65 return; 66 67 ProgramStateRef StInBound, StOutBound; 68 std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount); 69 if (StOutBound && !StInBound) { 70 ExplodedNode *N = C.generateErrorNode(StOutBound); 71 72 if (!N) 73 return; 74 75 // FIXME: This bug correspond to CWE-466. Eventually we should have bug 76 // types explicitly reference such exploit categories (when applicable). 77 if (!BT) 78 BT.reset(new BuiltinBug( 79 this, "Buffer overflow", 80 "Returned pointer value points outside the original object " 81 "(potential buffer overflow)")); 82 83 // Generate a report for this bug. 84 auto Report = 85 std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N); 86 Report->addRange(RetE->getSourceRange()); 87 88 const auto ConcreteElementCount = ElementCount.getAs<nonloc::ConcreteInt>(); 89 const auto ConcreteIdx = Idx.getAs<nonloc::ConcreteInt>(); 90 91 const auto *DeclR = ER->getSuperRegion()->getAs<DeclRegion>(); 92 93 if (DeclR) 94 Report->addNote("Original object declared here", 95 {DeclR->getDecl(), C.getSourceManager()}); 96 97 if (ConcreteElementCount) { 98 SmallString<128> SBuf; 99 llvm::raw_svector_ostream OS(SBuf); 100 OS << "Original object "; 101 if (DeclR) { 102 OS << "'"; 103 DeclR->getDecl()->printName(OS); 104 OS << "' "; 105 } 106 OS << "is an array of " << ConcreteElementCount->getValue() << " '"; 107 ER->getValueType().print(OS, 108 PrintingPolicy(C.getASTContext().getLangOpts())); 109 OS << "' objects"; 110 if (ConcreteIdx) { 111 OS << ", returned pointer points at index " << ConcreteIdx->getValue(); 112 } 113 114 Report->addNote(SBuf, 115 {RetE, C.getSourceManager(), C.getLocationContext()}); 116 } 117 118 bugreporter::trackExpressionValue(N, RetE, *Report); 119 120 C.emitReport(std::move(Report)); 121 } 122 } 123 124 void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) { 125 mgr.registerChecker<ReturnPointerRangeChecker>(); 126 } 127 128 bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) { 129 return true; 130 } 131