1//== ObjCContainersChecker.cpp - Path sensitive checker for CFArray *- C++ -*=//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Performs path sensitive checks of Core Foundation static containers like
11// CFArray.
12// 1) Check for buffer overflows:
13//      In CFArrayGetArrayAtIndex( myArray, index), if the index is outside the
14//      index space of theArray (0 to N-1 inclusive (where N is the count of
15//      theArray), the behavior is undefined.
16//
17//===----------------------------------------------------------------------===//
18
19#include "ClangSACheckers.h"
20#include "clang/AST/ParentMap.h"
21#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
22#include "clang/StaticAnalyzer/Core/Checker.h"
23#include "clang/StaticAnalyzer/Core/CheckerManager.h"
24#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
25#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
26
27using namespace clang;
28using namespace ento;
29
30namespace {
31class ObjCContainersChecker : public Checker< check::PreStmt<CallExpr>,
32                                             check::PostStmt<CallExpr>,
33                                             check::PointerEscape> {
34  mutable std::unique_ptr<BugType> BT;
35  inline void initBugType() const {
36    if (!BT)
37      BT.reset(new BugType(this, "CFArray API",
38                           categories::CoreFoundationObjectiveC));
39  }
40
41  inline SymbolRef getArraySym(const Expr *E, CheckerContext &C) const {
42    SVal ArrayRef = C.getState()->getSVal(E, C.getLocationContext());
43    SymbolRef ArraySym = ArrayRef.getAsSymbol();
44    return ArraySym;
45  }
46
47  void addSizeInfo(const Expr *Array, const Expr *Size,
48                   CheckerContext &C) const;
49
50public:
51  /// A tag to id this checker.
52  static void *getTag() { static int Tag; return &Tag; }
53
54  void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
55  void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
56  ProgramStateRef checkPointerEscape(ProgramStateRef State,
57                                     const InvalidatedSymbols &Escaped,
58                                     const CallEvent *Call,
59                                     PointerEscapeKind Kind) const;
60};
61} // end anonymous namespace
62
63// ProgramState trait - a map from array symbol to its state.
64REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
65
66void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
67                                        CheckerContext &C) const {
68  ProgramStateRef State = C.getState();
69  SVal SizeV = State->getSVal(Size, C.getLocationContext());
70  // Undefined is reported by another checker.
71  if (SizeV.isUnknownOrUndef())
72    return;
73
74  // Get the ArrayRef symbol.
75  SVal ArrayRef = State->getSVal(Array, C.getLocationContext());
76  SymbolRef ArraySym = ArrayRef.getAsSymbol();
77  if (!ArraySym)
78    return;
79
80  C.addTransition(
81      State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
82}
83
84void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
85                                          CheckerContext &C) const {
86  StringRef Name = C.getCalleeName(CE);
87  if (Name.empty() || CE->getNumArgs() < 1)
88    return;
89
90  // Add array size information to the state.
91  if (Name.equals("CFArrayCreate")) {
92    if (CE->getNumArgs() < 3)
93      return;
94    // Note, we can visit the Create method in the post-visit because
95    // the CFIndex parameter is passed in by value and will not be invalidated
96    // by the call.
97    addSizeInfo(CE, CE->getArg(2), C);
98    return;
99  }
100
101  if (Name.equals("CFArrayGetCount")) {
102    addSizeInfo(CE->getArg(0), CE, C);
103    return;
104  }
105}
106
107void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
108                                         CheckerContext &C) const {
109  StringRef Name = C.getCalleeName(CE);
110  if (Name.empty() || CE->getNumArgs() < 2)
111    return;
112
113  // Check the array access.
114  if (Name.equals("CFArrayGetValueAtIndex")) {
115    ProgramStateRef State = C.getState();
116    // Retrieve the size.
117    // Find out if we saw this array symbol before and have information about
118    // it.
119    const Expr *ArrayExpr = CE->getArg(0);
120    SymbolRef ArraySym = getArraySym(ArrayExpr, C);
121    if (!ArraySym)
122      return;
123
124    const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
125
126    if (!Size)
127      return;
128
129    // Get the index.
130    const Expr *IdxExpr = CE->getArg(1);
131    SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
132    if (IdxVal.isUnknownOrUndef())
133      return;
134    DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
135
136    // Now, check if 'Idx in [0, Size-1]'.
137    const QualType T = IdxExpr->getType();
138    ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
139    ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
140    if (StOutBound && !StInBound) {
141      ExplodedNode *N = C.generateErrorNode(StOutBound);
142      if (!N)
143        return;
144      initBugType();
145      auto R = llvm::make_unique<BugReport>(*BT, "Index is out of bounds", N);
146      R->addRange(IdxExpr->getSourceRange());
147      C.emitReport(std::move(R));
148      return;
149    }
150  }
151}
152
153ProgramStateRef
154ObjCContainersChecker::checkPointerEscape(ProgramStateRef State,
155                                          const InvalidatedSymbols &Escaped,
156                                          const CallEvent *Call,
157                                          PointerEscapeKind Kind) const {
158  for (const auto &Sym : Escaped) {
159    // When a symbol for a mutable array escapes, we can't reason precisely
160    // about its size any more -- so remove it from the map.
161    // Note that we aren't notified here when a CFMutableArrayRef escapes as a
162    // CFArrayRef. This is because CFArrayRef is typedef'd as a pointer to a
163    // const-qualified type.
164    State = State->remove<ArraySizeMap>(Sym);
165  }
166  return State;
167}
168
169/// Register checker.
170void ento::registerObjCContainersChecker(CheckerManager &mgr) {
171  mgr.registerChecker<ObjCContainersChecker>();
172}
173