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 23using namespace clang; 24using namespace ento; 25 26namespace { 27class ReturnPointerRangeChecker : 28 public Checker< check::PreStmt<ReturnStmt> > { 29 mutable std::unique_ptr<BuiltinBug> BT; 30 31public: 32 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const; 33}; 34} 35 36void 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 // Skip "body farmed" functions. 45 if (RetE->getSourceRange().isInvalid()) 46 return; 47 48 SVal V = C.getSVal(RetE); 49 const MemRegion *R = V.getAsRegion(); 50 51 const ElementRegion *ER = dyn_cast_or_null<ElementRegion>(R); 52 if (!ER) 53 return; 54 55 DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>(); 56 // Zero index is always in bound, this also passes ElementRegions created for 57 // pointer casts. 58 if (Idx.isZeroConstant()) 59 return; 60 61 // FIXME: All of this out-of-bounds checking should eventually be refactored 62 // into a common place. 63 DefinedOrUnknownSVal ElementCount = getDynamicElementCount( 64 state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType()); 65 66 // We assume that the location after the last element in the array is used as 67 // end() iterator. Reporting on these would return too many false positives. 68 if (Idx == ElementCount) 69 return; 70 71 ProgramStateRef StInBound, StOutBound; 72 std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount); 73 if (StOutBound && !StInBound) { 74 ExplodedNode *N = C.generateErrorNode(StOutBound); 75 76 if (!N) 77 return; 78 79 // FIXME: This bug correspond to CWE-466. Eventually we should have bug 80 // types explicitly reference such exploit categories (when applicable). 81 if (!BT) 82 BT.reset(new BuiltinBug( 83 this, "Buffer overflow", 84 "Returned pointer value points outside the original object " 85 "(potential buffer overflow)")); 86 87 // Generate a report for this bug. 88 auto Report = 89 std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N); 90 Report->addRange(RetE->getSourceRange()); 91 92 const auto ConcreteElementCount = ElementCount.getAs<nonloc::ConcreteInt>(); 93 const auto ConcreteIdx = Idx.getAs<nonloc::ConcreteInt>(); 94 95 const auto *DeclR = ER->getSuperRegion()->getAs<DeclRegion>(); 96 97 if (DeclR) 98 Report->addNote("Original object declared here", 99 {DeclR->getDecl(), C.getSourceManager()}); 100 101 if (ConcreteElementCount) { 102 SmallString<128> SBuf; 103 llvm::raw_svector_ostream OS(SBuf); 104 OS << "Original object "; 105 if (DeclR) { 106 OS << "'"; 107 DeclR->getDecl()->printName(OS); 108 OS << "' "; 109 } 110 OS << "is an array of " << ConcreteElementCount->getValue() << " '"; 111 ER->getValueType().print(OS, 112 PrintingPolicy(C.getASTContext().getLangOpts())); 113 OS << "' objects"; 114 if (ConcreteIdx) { 115 OS << ", returned pointer points at index " << ConcreteIdx->getValue(); 116 } 117 118 Report->addNote(SBuf, 119 {RetE, C.getSourceManager(), C.getLocationContext()}); 120 } 121 122 bugreporter::trackExpressionValue(N, RetE, *Report); 123 124 C.emitReport(std::move(Report)); 125 } 126} 127 128void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) { 129 mgr.registerChecker<ReturnPointerRangeChecker>(); 130} 131 132bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) { 133 return true; 134} 135