MacOSKeychainAPIChecker.cpp revision 083fcb208ee2c8c2e375c41482a92039282e6389 
1//==--- MacOSKeychainAPIChecker.cpp ------------------------------*- 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// This checker flags misuses of KeyChainAPI. In particular, the password data
10// allocated/returned by SecKeychainItemCopyContent,
11// SecKeychainFindGenericPassword, SecKeychainFindInternetPassword functions has
12// to be freed using a call to SecKeychainItemFreeContent.
13//===----------------------------------------------------------------------===//
14
15#include "ClangSACheckers.h"
16#include "clang/StaticAnalyzer/Core/Checker.h"
17#include "clang/StaticAnalyzer/Core/CheckerManager.h"
18#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/GRState.h"
21#include "clang/StaticAnalyzer/Core/PathSensitive/GRStateTrait.h"
22
23using namespace clang;
24using namespace ento;
25
26namespace {
27class MacOSKeychainAPIChecker : public Checker<check::PreStmt<CallExpr>,
28                                               check::PreStmt<ReturnStmt>,
29                                               check::PostStmt<CallExpr>,
30                                               check::EndPath > {
31  mutable llvm::OwningPtr<BugType> BT;
32
33public:
34  void checkPreStmt(const CallExpr *S, CheckerContext &C) const;
35  void checkPreStmt(const ReturnStmt *S, CheckerContext &C) const;
36  void checkPostStmt(const CallExpr *S, CheckerContext &C) const;
37
38  void checkEndPath(EndOfFunctionNodeBuilder &B, ExprEngine &Eng) const;
39
40private:
41  /// Stores the information about the allocator and deallocator functions -
42  /// these are the functions the checker is tracking.
43  struct ADFunctionInfo {
44    const char* Name;
45    unsigned int Param;
46    unsigned int DeallocatorIdx;
47  };
48  static const unsigned InvalidIdx = 100000;
49  static const unsigned FunctionsToTrackSize = 4;
50  static const ADFunctionInfo FunctionsToTrack[FunctionsToTrackSize];
51
52  /// Given the function name, returns the index of the allocator/deallocator
53  /// function.
54  unsigned getTrackedFunctionIndex(StringRef Name, bool IsAllocator) const;
55
56  inline void initBugType() const {
57    if (!BT)
58      BT.reset(new BugType("Improper use of SecKeychain API", "Mac OS API"));
59  }
60};
61}
62
63/// AllocationState is a part of the checker specific state together with the
64/// MemRegion corresponding to the allocated data.
65struct AllocationState {
66  const Expr *Address;
67  /// The index of the allocator function.
68  unsigned int AllocatorIdx;
69
70  AllocationState(const Expr *E, unsigned int Idx) : Address(E),
71                                                     AllocatorIdx(Idx) {}
72  bool operator==(const AllocationState &X) const {
73    return Address == X.Address;
74  }
75  void Profile(llvm::FoldingSetNodeID &ID) const {
76    ID.AddPointer(Address);
77    ID.AddInteger(AllocatorIdx);
78  }
79};
80
81/// GRState traits to store the currently allocated (and not yet freed) symbols.
82typedef llvm::ImmutableMap<const MemRegion*, AllocationState> AllocatedSetTy;
83
84namespace { struct AllocatedData {}; }
85namespace clang { namespace ento {
86template<> struct GRStateTrait<AllocatedData>
87    :  public GRStatePartialTrait<AllocatedSetTy > {
88  static void *GDMIndex() { static int index = 0; return &index; }
89};
90}}
91
92static bool isEnclosingFunctionParam(const Expr *E) {
93  E = E->IgnoreParenCasts();
94  if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
95    const ValueDecl *VD = DRE->getDecl();
96    if (isa<ImplicitParamDecl>(VD) || isa<ParmVarDecl>(VD))
97      return true;
98  }
99  return false;
100}
101
102const MacOSKeychainAPIChecker::ADFunctionInfo
103  MacOSKeychainAPIChecker::FunctionsToTrack[FunctionsToTrackSize] = {
104    {"SecKeychainItemCopyContent", 4, 3},                       // 0
105    {"SecKeychainFindGenericPassword", 6, 3},                   // 1
106    {"SecKeychainFindInternetPassword", 13, 3},                 // 2
107    {"SecKeychainItemFreeContent", 1, InvalidIdx},              // 3
108};
109
110unsigned MacOSKeychainAPIChecker::getTrackedFunctionIndex(StringRef Name,
111                                                       bool IsAllocator) const {
112  for (unsigned I = 0; I < FunctionsToTrackSize; ++I) {
113    ADFunctionInfo FI = FunctionsToTrack[I];
114    if (FI.Name != Name)
115      continue;
116    // Make sure the function is of the right type (allocator vs deallocator).
117    if (IsAllocator && (FI.DeallocatorIdx == InvalidIdx))
118      return InvalidIdx;
119    if (!IsAllocator && (FI.DeallocatorIdx != InvalidIdx))
120      return InvalidIdx;
121
122    return I;
123  }
124  // The function is not tracked.
125  return InvalidIdx;
126}
127
128void MacOSKeychainAPIChecker::checkPreStmt(const CallExpr *CE,
129                                           CheckerContext &C) const {
130  const GRState *State = C.getState();
131  const Expr *Callee = CE->getCallee();
132  SVal L = State->getSVal(Callee);
133
134  const FunctionDecl *funDecl = L.getAsFunctionDecl();
135  if (!funDecl)
136    return;
137  IdentifierInfo *funI = funDecl->getIdentifier();
138  if (!funI)
139    return;
140  StringRef funName = funI->getName();
141
142  // If a value has been freed, remove from the list.
143  unsigned idx = getTrackedFunctionIndex(funName, false);
144  if (idx == InvalidIdx)
145    return;
146
147  const Expr *ArgExpr = CE->getArg(FunctionsToTrack[idx].Param);
148  const MemRegion *Arg = State->getSVal(ArgExpr).getAsRegion();
149  if (!Arg)
150    return;
151
152  // If trying to free data which has not been allocated yet, report as bug.
153  const AllocationState *AS = State->get<AllocatedData>(Arg);
154  if (!AS) {
155    // It is possible that this is a false positive - the argument might
156    // have entered as an enclosing function parameter.
157    if (isEnclosingFunctionParam(ArgExpr))
158      return;
159
160    ExplodedNode *N = C.generateNode(State);
161    if (!N)
162      return;
163    initBugType();
164    RangedBugReport *Report = new RangedBugReport(*BT,
165        "Trying to free data which has not been allocated.", N);
166    Report->addRange(ArgExpr->getSourceRange());
167    C.EmitReport(Report);
168    return;
169  }
170
171  // Continue exploring from the new state.
172  assert(FunctionsToTrack[AS->AllocatorIdx].DeallocatorIdx == idx &&
173    "Allocator should match the deallocator");
174  State = State->remove<AllocatedData>(Arg);
175  C.addTransition(State);
176}
177
178void MacOSKeychainAPIChecker::checkPostStmt(const CallExpr *CE,
179                                            CheckerContext &C) const {
180  const GRState *State = C.getState();
181  const Expr *Callee = CE->getCallee();
182  SVal L = State->getSVal(Callee);
183  StoreManager& SM = C.getStoreManager();
184
185  const FunctionDecl *funDecl = L.getAsFunctionDecl();
186  if (!funDecl)
187    return;
188  IdentifierInfo *funI = funDecl->getIdentifier();
189  if (!funI)
190    return;
191  StringRef funName = funI->getName();
192
193  // If a value has been allocated, add it to the set for tracking.
194  unsigned idx = getTrackedFunctionIndex(funName, true);
195  if (idx == InvalidIdx)
196    return;
197
198  const Expr *ArgExpr = CE->getArg(FunctionsToTrack[idx].Param);
199  SVal Arg = State->getSVal(ArgExpr);
200  if (const loc::MemRegionVal *X = dyn_cast<loc::MemRegionVal>(&Arg)) {
201    // Add the symbolic value, which represents the location of the allocated
202    // data, to the set.
203    const MemRegion *V = SM.Retrieve(State->getStore(), *X).getAsRegion();
204    // If this is not a region, it can be:
205    //  - unknown (cannot reason about it)
206    //  - undefined (already reported by other checker)
207    //  - constant (null - should not be tracked,
208    //              other constant will generate a compiler warning)
209    //  - goto (should be reported by other checker)
210    if (!V)
211      return;
212
213    State = State->set<AllocatedData>(V, AllocationState(ArgExpr, idx));
214
215    // We only need to track the value if the function returned noErr(0), so
216    // bind the return value of the function to 0.
217    SValBuilder &Builder = C.getSValBuilder();
218    SVal ZeroVal = Builder.makeZeroVal(Builder.getContext().CharTy);
219    State = State->BindExpr(CE, ZeroVal);
220    assert(State);
221
222    // Proceed from the new state.
223    C.addTransition(State);
224  }
225}
226
227void MacOSKeychainAPIChecker::checkPreStmt(const ReturnStmt *S,
228                                           CheckerContext &C) const {
229  const Expr *retExpr = S->getRetValue();
230  if (!retExpr)
231    return;
232
233  // Check  if the value is escaping through the return.
234  const GRState *state = C.getState();
235  const MemRegion *V = state->getSVal(retExpr).getAsRegion();
236  if (!V)
237    return;
238  state = state->remove<AllocatedData>(V);
239
240  // Proceed from the new state.
241  C.addTransition(state);
242}
243
244void MacOSKeychainAPIChecker::checkEndPath(EndOfFunctionNodeBuilder &B,
245                                           ExprEngine &Eng) const {
246  const GRState *state = B.getState();
247  AllocatedSetTy AS = state->get<AllocatedData>();
248  ExplodedNode *N = B.generateNode(state);
249  if (!N)
250    return;
251  initBugType();
252
253  // Anything which has been allocated but not freed (nor escaped) will be
254  // found here, so report it.
255  for (AllocatedSetTy::iterator I = AS.begin(), E = AS.end(); I != E; ++I ) {
256    RangedBugReport *Report = new RangedBugReport(*BT,
257      "Missing a call to SecKeychainItemFreeContent.", N);
258    // TODO: The report has to mention the expression which contains the
259    // allocated content as well as the point at which it has been allocated.
260    // Currently, the next line is useless.
261    Report->addRange(I->second.Address->getSourceRange());
262    Eng.getBugReporter().EmitReport(Report);
263  }
264}
265
266void ento::registerMacOSKeychainAPIChecker(CheckerManager &mgr) {
267  mgr.registerChecker<MacOSKeychainAPIChecker>();
268}
269