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
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const36 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 = state->assumeInBound(Idx, ElementCount, true);
68 ProgramStateRef StOutBound = state->assumeInBound(Idx, ElementCount, false);
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
registerReturnPointerRangeChecker(CheckerManager & mgr)124 void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) {
125 mgr.registerChecker<ReturnPointerRangeChecker>();
126 }
127
shouldRegisterReturnPointerRangeChecker(const CheckerManager & mgr)128 bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) {
129 return true;
130 }
131