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 
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   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, StOutBound;
68   std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount);
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 
124 void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) {
125   mgr.registerChecker<ReturnPointerRangeChecker>();
126 }
127 
128 bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) {
129   return true;
130 }
131