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<BugType> 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 // 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 BugType(this, "Buffer overflow")); 83 constexpr llvm::StringLiteral Msg = 84 "Returned pointer value points outside the original object " 85 "(potential buffer overflow)"; 86 87 // Generate a report for this bug. 88 auto Report = std::make_unique<PathSensitiveBugReport>(*BT, Msg, N); 89 Report->addRange(RetE->getSourceRange()); 90 91 const auto ConcreteElementCount = ElementCount.getAs<nonloc::ConcreteInt>(); 92 const auto ConcreteIdx = Idx.getAs<nonloc::ConcreteInt>(); 93 94 const auto *DeclR = ER->getSuperRegion()->getAs<DeclRegion>(); 95 96 if (DeclR) 97 Report->addNote("Original object declared here", 98 {DeclR->getDecl(), C.getSourceManager()}); 99 100 if (ConcreteElementCount) { 101 SmallString<128> SBuf; 102 llvm::raw_svector_ostream OS(SBuf); 103 OS << "Original object "; 104 if (DeclR) { 105 OS << "'"; 106 DeclR->getDecl()->printName(OS); 107 OS << "' "; 108 } 109 OS << "is an array of " << ConcreteElementCount->getValue() << " '"; 110 ER->getValueType().print(OS, 111 PrintingPolicy(C.getASTContext().getLangOpts())); 112 OS << "' objects"; 113 if (ConcreteIdx) { 114 OS << ", returned pointer points at index " << ConcreteIdx->getValue(); 115 } 116 117 Report->addNote(SBuf, 118 {RetE, C.getSourceManager(), C.getLocationContext()}); 119 } 120 121 bugreporter::trackExpressionValue(N, RetE, *Report); 122 123 C.emitReport(std::move(Report)); 124 } 125 } 126 127 void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) { 128 mgr.registerChecker<ReturnPointerRangeChecker>(); 129 } 130 131 bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) { 132 return true; 133 } 134