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/BugType.h" 16 #include "clang/StaticAnalyzer/Core/Checker.h" 17 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 19 #include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h" 20 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h" 21 22 using namespace clang; 23 using namespace ento; 24 25 namespace { 26 class ReturnPointerRangeChecker : 27 public Checker< check::PreStmt<ReturnStmt> > { 28 mutable std::unique_ptr<BuiltinBug> BT; 29 30 public: 31 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const; 32 }; 33 } 34 35 void ReturnPointerRangeChecker::checkPreStmt(const ReturnStmt *RS, 36 CheckerContext &C) const { 37 ProgramStateRef state = C.getState(); 38 39 const Expr *RetE = RS->getRetValue(); 40 if (!RetE) 41 return; 42 43 SVal V = C.getSVal(RetE); 44 const MemRegion *R = V.getAsRegion(); 45 46 const ElementRegion *ER = dyn_cast_or_null<ElementRegion>(R); 47 if (!ER) 48 return; 49 50 DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>(); 51 // Zero index is always in bound, this also passes ElementRegions created for 52 // pointer casts. 53 if (Idx.isZeroConstant()) 54 return; 55 56 // FIXME: All of this out-of-bounds checking should eventually be refactored 57 // into a common place. 58 DefinedOrUnknownSVal ElementCount = getDynamicElementCount( 59 state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType()); 60 61 // We assume that the location after the last element in the array is used as 62 // end() iterator. Reporting on these would return too many false positives. 63 if (Idx == ElementCount) 64 return; 65 66 ProgramStateRef StInBound = state->assumeInBound(Idx, ElementCount, true); 67 ProgramStateRef StOutBound = state->assumeInBound(Idx, ElementCount, false); 68 if (StOutBound && !StInBound) { 69 ExplodedNode *N = C.generateErrorNode(StOutBound); 70 71 if (!N) 72 return; 73 74 // FIXME: This bug correspond to CWE-466. Eventually we should have bug 75 // types explicitly reference such exploit categories (when applicable). 76 if (!BT) 77 BT.reset(new BuiltinBug( 78 this, "Buffer overflow", 79 "Returned pointer value points outside the original object " 80 "(potential buffer overflow)")); 81 82 // FIXME: It would be nice to eventually make this diagnostic more clear, 83 // e.g., by referencing the original declaration or by saying *why* this 84 // reference is outside the range. 85 86 // Generate a report for this bug. 87 auto report = 88 std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N); 89 90 report->addRange(RetE->getSourceRange()); 91 C.emitReport(std::move(report)); 92 } 93 } 94 95 void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) { 96 mgr.registerChecker<ReturnPointerRangeChecker>(); 97 } 98 99 bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) { 100 return true; 101 } 102