StackAddrEscapeChecker.cpp revision 651f13cea278ec967336033dd032faef0e9fc2ec 
1//=== StackAddrEscapeChecker.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//
10// This file defines stack address leak checker, which checks if an invalid
11// stack address is stored into a global or heap location. See CERT DCL30-C.
12//
13//===----------------------------------------------------------------------===//
14
15#include "ClangSACheckers.h"
16#include "clang/AST/ExprCXX.h"
17#include "clang/Basic/SourceManager.h"
18#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
19#include "clang/StaticAnalyzer/Core/Checker.h"
20#include "clang/StaticAnalyzer/Core/CheckerManager.h"
21#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
22#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
23#include "llvm/ADT/SmallString.h"
24#include "llvm/Support/raw_ostream.h"
25using namespace clang;
26using namespace ento;
27
28namespace {
29class StackAddrEscapeChecker : public Checker< check::PreStmt<ReturnStmt>,
30                                               check::EndFunction > {
31  mutable std::unique_ptr<BuiltinBug> BT_stackleak;
32  mutable std::unique_ptr<BuiltinBug> BT_returnstack;
33
34public:
35  void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
36  void checkEndFunction(CheckerContext &Ctx) const;
37private:
38  void EmitStackError(CheckerContext &C, const MemRegion *R,
39                      const Expr *RetE) const;
40  static SourceRange genName(raw_ostream &os, const MemRegion *R,
41                             ASTContext &Ctx);
42};
43}
44
45SourceRange StackAddrEscapeChecker::genName(raw_ostream &os, const MemRegion *R,
46                                            ASTContext &Ctx) {
47    // Get the base region, stripping away fields and elements.
48  R = R->getBaseRegion();
49  SourceManager &SM = Ctx.getSourceManager();
50  SourceRange range;
51  os << "Address of ";
52
53  // Check if the region is a compound literal.
54  if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) {
55    const CompoundLiteralExpr *CL = CR->getLiteralExpr();
56    os << "stack memory associated with a compound literal "
57          "declared on line "
58        << SM.getExpansionLineNumber(CL->getLocStart())
59        << " returned to caller";
60    range = CL->getSourceRange();
61  }
62  else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
63    const Expr *ARE = AR->getExpr();
64    SourceLocation L = ARE->getLocStart();
65    range = ARE->getSourceRange();
66    os << "stack memory allocated by call to alloca() on line "
67       << SM.getExpansionLineNumber(L);
68  }
69  else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
70    const BlockDecl *BD = BR->getCodeRegion()->getDecl();
71    SourceLocation L = BD->getLocStart();
72    range = BD->getSourceRange();
73    os << "stack-allocated block declared on line "
74       << SM.getExpansionLineNumber(L);
75  }
76  else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
77    os << "stack memory associated with local variable '"
78       << VR->getString() << '\'';
79    range = VR->getDecl()->getSourceRange();
80  }
81  else if (const CXXTempObjectRegion *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
82    QualType Ty = TOR->getValueType().getLocalUnqualifiedType();
83    os << "stack memory associated with temporary object of type '";
84    Ty.print(os, Ctx.getPrintingPolicy());
85    os << "'";
86    range = TOR->getExpr()->getSourceRange();
87  }
88  else {
89    llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
90  }
91
92  return range;
93}
94
95void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
96                                          const Expr *RetE) const {
97  ExplodedNode *N = C.generateSink();
98
99  if (!N)
100    return;
101
102  if (!BT_returnstack)
103    BT_returnstack.reset(
104        new BuiltinBug(this, "Return of address to stack-allocated memory"));
105
106  // Generate a report for this bug.
107  SmallString<512> buf;
108  llvm::raw_svector_ostream os(buf);
109  SourceRange range = genName(os, R, C.getASTContext());
110  os << " returned to caller";
111  BugReport *report = new BugReport(*BT_returnstack, os.str(), N);
112  report->addRange(RetE->getSourceRange());
113  if (range.isValid())
114    report->addRange(range);
115
116  C.emitReport(report);
117}
118
119void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
120                                          CheckerContext &C) const {
121
122  const Expr *RetE = RS->getRetValue();
123  if (!RetE)
124    return;
125  RetE = RetE->IgnoreParens();
126
127  const LocationContext *LCtx = C.getLocationContext();
128  SVal V = C.getState()->getSVal(RetE, LCtx);
129  const MemRegion *R = V.getAsRegion();
130
131  if (!R)
132    return;
133
134  const StackSpaceRegion *SS =
135    dyn_cast_or_null<StackSpaceRegion>(R->getMemorySpace());
136
137  if (!SS)
138    return;
139
140  // Return stack memory in an ancestor stack frame is fine.
141  const StackFrameContext *CurFrame = LCtx->getCurrentStackFrame();
142  const StackFrameContext *MemFrame = SS->getStackFrame();
143  if (MemFrame != CurFrame)
144    return;
145
146  // Automatic reference counting automatically copies blocks.
147  if (C.getASTContext().getLangOpts().ObjCAutoRefCount &&
148      isa<BlockDataRegion>(R))
149    return;
150
151  // Returning a record by value is fine. (In this case, the returned
152  // expression will be a copy-constructor, possibly wrapped in an
153  // ExprWithCleanups node.)
154  if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
155    RetE = Cleanup->getSubExpr();
156  if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
157    return;
158
159  EmitStackError(C, R, RetE);
160}
161
162void StackAddrEscapeChecker::checkEndFunction(CheckerContext &Ctx) const {
163  ProgramStateRef state = Ctx.getState();
164
165  // Iterate over all bindings to global variables and see if it contains
166  // a memory region in the stack space.
167  class CallBack : public StoreManager::BindingsHandler {
168  private:
169    CheckerContext &Ctx;
170    const StackFrameContext *CurSFC;
171  public:
172    SmallVector<std::pair<const MemRegion*, const MemRegion*>, 10> V;
173
174    CallBack(CheckerContext &CC) :
175      Ctx(CC),
176      CurSFC(CC.getLocationContext()->getCurrentStackFrame())
177    {}
178
179    bool HandleBinding(StoreManager &SMgr, Store store,
180                       const MemRegion *region, SVal val) override {
181
182      if (!isa<GlobalsSpaceRegion>(region->getMemorySpace()))
183        return true;
184
185      const MemRegion *vR = val.getAsRegion();
186      if (!vR)
187        return true;
188
189      // Under automated retain release, it is okay to assign a block
190      // directly to a global variable.
191      if (Ctx.getASTContext().getLangOpts().ObjCAutoRefCount &&
192          isa<BlockDataRegion>(vR))
193        return true;
194
195      if (const StackSpaceRegion *SSR =
196          dyn_cast<StackSpaceRegion>(vR->getMemorySpace())) {
197        // If the global variable holds a location in the current stack frame,
198        // record the binding to emit a warning.
199        if (SSR->getStackFrame() == CurSFC)
200          V.push_back(std::make_pair(region, vR));
201      }
202
203      return true;
204    }
205  };
206
207  CallBack cb(Ctx);
208  state->getStateManager().getStoreManager().iterBindings(state->getStore(),cb);
209
210  if (cb.V.empty())
211    return;
212
213  // Generate an error node.
214  ExplodedNode *N = Ctx.addTransition(state);
215  if (!N)
216    return;
217
218  if (!BT_stackleak)
219    BT_stackleak.reset(
220        new BuiltinBug(this, "Stack address stored into global variable",
221                       "Stack address was saved into a global variable. "
222                       "This is dangerous because the address will become "
223                       "invalid after returning from the function"));
224
225  for (unsigned i = 0, e = cb.V.size(); i != e; ++i) {
226    // Generate a report for this bug.
227    SmallString<512> buf;
228    llvm::raw_svector_ostream os(buf);
229    SourceRange range = genName(os, cb.V[i].second, Ctx.getASTContext());
230    os << " is still referred to by the global variable '";
231    const VarRegion *VR = cast<VarRegion>(cb.V[i].first->getBaseRegion());
232    os << *VR->getDecl()
233       << "' upon returning to the caller.  This will be a dangling reference";
234    BugReport *report = new BugReport(*BT_stackleak, os.str(), N);
235    if (range.isValid())
236      report->addRange(range);
237
238    Ctx.emitReport(report);
239  }
240}
241
242void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
243  mgr.registerChecker<StackAddrEscapeChecker>();
244}
245