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