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   // 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 BuiltinBug(
83           this, "Buffer overflow",
84           "Returned pointer value points outside the original object "
85           "(potential buffer overflow)"));
86 
87     // Generate a report for this bug.
88     auto Report =
89         std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N);
90     Report->addRange(RetE->getSourceRange());
91 
92     const auto ConcreteElementCount = ElementCount.getAs<nonloc::ConcreteInt>();
93     const auto ConcreteIdx = Idx.getAs<nonloc::ConcreteInt>();
94 
95     const auto *DeclR = ER->getSuperRegion()->getAs<DeclRegion>();
96 
97     if (DeclR)
98       Report->addNote("Original object declared here",
99                       {DeclR->getDecl(), C.getSourceManager()});
100 
101     if (ConcreteElementCount) {
102       SmallString<128> SBuf;
103       llvm::raw_svector_ostream OS(SBuf);
104       OS << "Original object ";
105       if (DeclR) {
106         OS << "'";
107         DeclR->getDecl()->printName(OS);
108         OS << "' ";
109       }
110       OS << "is an array of " << ConcreteElementCount->getValue() << " '";
111       ER->getValueType().print(OS,
112                                PrintingPolicy(C.getASTContext().getLangOpts()));
113       OS << "' objects";
114       if (ConcreteIdx) {
115         OS << ", returned pointer points at index " << ConcreteIdx->getValue();
116       }
117 
118       Report->addNote(SBuf,
119                       {RetE, C.getSourceManager(), C.getLocationContext()});
120     }
121 
122     bugreporter::trackExpressionValue(N, RetE, *Report);
123 
124     C.emitReport(std::move(Report));
125   }
126 }
127 
128 void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) {
129   mgr.registerChecker<ReturnPointerRangeChecker>();
130 }
131 
132 bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) {
133   return true;
134 }
135