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
23using namespace clang;
24using namespace ento;
25
26namespace {
27class ReturnPointerRangeChecker :
28    public Checker< check::PreStmt<ReturnStmt> > {
29  mutable std::unique_ptr<BuiltinBug> BT;
30
31public:
32    void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
33};
34}
35
36void 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
128void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) {
129  mgr.registerChecker<ReturnPointerRangeChecker>();
130}
131
132bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) {
133  return true;
134}
135