132 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// This file defines ReturnPointerRangeChecker, which is a path-sensitive check10// 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 // FIXME: This bug correspond to CWE-466. Eventually we should have bug30 // types explicitly reference such exploit categories (when applicable).31 const BugType BT{this, "Buffer overflow"};32 33public:34 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;35};36}37 38void ReturnPointerRangeChecker::checkPreStmt(const ReturnStmt *RS,39 CheckerContext &C) const {40 ProgramStateRef state = C.getState();41 42 const Expr *RetE = RS->getRetValue();43 if (!RetE)44 return;45 46 // Skip "body farmed" functions.47 if (RetE->getSourceRange().isInvalid())48 return;49 50 SVal V = C.getSVal(RetE);51 const MemRegion *R = V.getAsRegion();52 53 const ElementRegion *ER = dyn_cast_or_null<ElementRegion>(R);54 if (!ER)55 return;56 57 DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();58 // Zero index is always in bound, this also passes ElementRegions created for59 // pointer casts.60 if (Idx.isZeroConstant())61 return;62 63 // FIXME: All of this out-of-bounds checking should eventually be refactored64 // into a common place.65 DefinedOrUnknownSVal ElementCount = getDynamicElementCount(66 state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());67 68 // We assume that the location after the last element in the array is used as69 // end() iterator. Reporting on these would return too many false positives.70 if (Idx == ElementCount)71 return;72 73 ProgramStateRef StInBound, StOutBound;74 std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount);75 if (StOutBound && !StInBound) {76 ExplodedNode *N = C.generateErrorNode(StOutBound);77 78 if (!N)79 return;80 81 constexpr llvm::StringLiteral Msg =82 "Returned pointer value points outside the original object "83 "(potential buffer overflow)";84 85 // Generate a report for this bug.86 auto Report = std::make_unique<PathSensitiveBugReport>(BT, Msg, N);87 Report->addRange(RetE->getSourceRange());88 89 const auto ConcreteElementCount = ElementCount.getAs<nonloc::ConcreteInt>();90 const auto ConcreteIdx = Idx.getAs<nonloc::ConcreteInt>();91 92 const auto *DeclR = ER->getSuperRegion()->getAs<DeclRegion>();93 94 if (DeclR)95 Report->addNote("Original object declared here",96 {DeclR->getDecl(), C.getSourceManager()});97 98 if (ConcreteElementCount) {99 SmallString<128> SBuf;100 llvm::raw_svector_ostream OS(SBuf);101 OS << "Original object ";102 if (DeclR) {103 OS << "'";104 DeclR->getDecl()->printName(OS);105 OS << "' ";106 }107 OS << "is an array of " << ConcreteElementCount->getValue() << " '";108 ER->getValueType().print(OS,109 PrintingPolicy(C.getASTContext().getLangOpts()));110 OS << "' objects";111 if (ConcreteIdx) {112 OS << ", returned pointer points at index " << ConcreteIdx->getValue();113 }114 115 Report->addNote(SBuf,116 {RetE, C.getSourceManager(), C.getLocationContext()});117 }118 119 bugreporter::trackExpressionValue(N, RetE, *Report);120 121 C.emitReport(std::move(Report));122 }123}124 125void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) {126 mgr.registerChecker<ReturnPointerRangeChecker>();127}128 129bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) {130 return true;131}132