StackAddrEscapeChecker.cpp revision 5f9e272e632e951b1efe824cd16acb4d96077930 
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/StaticAnalyzer/Core/Checker.h"
17#include "clang/StaticAnalyzer/Core/CheckerManager.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/GRState.h"
21#include "clang/Basic/SourceManager.h"
22#include "llvm/ADT/SmallString.h"
23using namespace clang;
24using namespace ento;
25
26namespace {
27class StackAddrEscapeChecker : public Checker< check::PreStmt<ReturnStmt>,
28                                               check::EndPath > {
29  mutable llvm::OwningPtr<BuiltinBug> BT_stackleak;
30  mutable llvm::OwningPtr<BuiltinBug> BT_returnstack;
31
32public:
33  void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
34  void checkEndPath(EndOfFunctionNodeBuilder &B, ExprEngine &Eng) const;
35private:
36  void EmitStackError(CheckerContext &C, const MemRegion *R,
37                      const Expr *RetE) const;
38  static SourceRange GenName(raw_ostream &os, const MemRegion *R,
39                             SourceManager &SM);
40};
41}
42
43SourceRange StackAddrEscapeChecker::GenName(raw_ostream &os,
44                                          const MemRegion *R,
45                                          SourceManager &SM) {
46    // Get the base region, stripping away fields and elements.
47  R = R->getBaseRegion();
48  SourceRange range;
49  os << "Address of ";
50
51  // Check if the region is a compound literal.
52  if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) {
53    const CompoundLiteralExpr* CL = CR->getLiteralExpr();
54    os << "stack memory associated with a compound literal "
55          "declared on line "
56        << SM.getInstantiationLineNumber(CL->getLocStart())
57        << " returned to caller";
58    range = CL->getSourceRange();
59  }
60  else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
61    const Expr* ARE = AR->getExpr();
62    SourceLocation L = ARE->getLocStart();
63    range = ARE->getSourceRange();
64    os << "stack memory allocated by call to alloca() on line "
65       << SM.getInstantiationLineNumber(L);
66  }
67  else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
68    const BlockDecl *BD = BR->getCodeRegion()->getDecl();
69    SourceLocation L = BD->getLocStart();
70    range = BD->getSourceRange();
71    os << "stack-allocated block declared on line "
72       << SM.getInstantiationLineNumber(L);
73  }
74  else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
75    os << "stack memory associated with local variable '"
76       << VR->getString() << '\'';
77    range = VR->getDecl()->getSourceRange();
78  }
79  else {
80    assert(false && "Invalid region in ReturnStackAddressChecker.");
81  }
82
83  return range;
84}
85
86void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
87                                          const Expr *RetE) const {
88  ExplodedNode *N = C.generateSink();
89
90  if (!N)
91    return;
92
93  if (!BT_returnstack)
94   BT_returnstack.reset(
95                 new BuiltinBug("Return of address to stack-allocated memory"));
96
97  // Generate a report for this bug.
98  llvm::SmallString<512> buf;
99  llvm::raw_svector_ostream os(buf);
100  SourceRange range = GenName(os, R, C.getSourceManager());
101  os << " returned to caller";
102  RangedBugReport *report = new RangedBugReport(*BT_returnstack, os.str(), N);
103  report->addRange(RetE->getSourceRange());
104  if (range.isValid())
105    report->addRange(range);
106
107  C.EmitReport(report);
108}
109
110void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
111                                        CheckerContext &C) const {
112
113  const Expr *RetE = RS->getRetValue();
114  if (!RetE)
115    return;
116
117  SVal V = C.getState()->getSVal(RetE);
118  const MemRegion *R = V.getAsRegion();
119
120  if (!R || !R->hasStackStorage())
121    return;
122
123  if (R->hasStackStorage()) {
124    // Automatic reference counting automatically copies blocks.
125    if (C.getASTContext().getLangOptions().ObjCAutoRefCount &&
126        isa<BlockDataRegion>(R))
127      return;
128
129    EmitStackError(C, R, RetE);
130    return;
131  }
132}
133
134void StackAddrEscapeChecker::checkEndPath(EndOfFunctionNodeBuilder &B,
135                                        ExprEngine &Eng) const {
136
137  const GRState *state = B.getState();
138
139  // Iterate over all bindings to global variables and see if it contains
140  // a memory region in the stack space.
141  class CallBack : public StoreManager::BindingsHandler {
142  private:
143    ExprEngine &Eng;
144    const StackFrameContext *CurSFC;
145  public:
146    SmallVector<std::pair<const MemRegion*, const MemRegion*>, 10> V;
147
148    CallBack(ExprEngine &Eng, const LocationContext *LCtx)
149      : Eng(Eng), CurSFC(LCtx->getCurrentStackFrame()) {}
150
151    bool HandleBinding(StoreManager &SMgr, Store store,
152                       const MemRegion *region, SVal val) {
153
154      if (!isa<GlobalsSpaceRegion>(region->getMemorySpace()))
155        return true;
156
157      const MemRegion *vR = val.getAsRegion();
158      if (!vR)
159        return true;
160
161      // Under automated retain release, it is okay to assign a block
162      // directly to a global variable.
163      if (Eng.getContext().getLangOptions().ObjCAutoRefCount &&
164          isa<BlockDataRegion>(vR))
165        return true;
166
167      if (const StackSpaceRegion *SSR =
168          dyn_cast<StackSpaceRegion>(vR->getMemorySpace())) {
169        // If the global variable holds a location in the current stack frame,
170        // record the binding to emit a warning.
171        if (SSR->getStackFrame() == CurSFC)
172          V.push_back(std::make_pair(region, vR));
173      }
174
175      return true;
176    }
177  };
178
179  CallBack cb(Eng, B.getPredecessor()->getLocationContext());
180  state->getStateManager().getStoreManager().iterBindings(state->getStore(),cb);
181
182  if (cb.V.empty())
183    return;
184
185  // Generate an error node.
186  ExplodedNode *N = B.generateNode(state);
187  if (!N)
188    return;
189
190  if (!BT_stackleak)
191    BT_stackleak.reset(
192      new BuiltinBug("Stack address stored into global variable",
193                     "Stack address was saved into a global variable. "
194                     "This is dangerous because the address will become "
195                     "invalid after returning from the function"));
196
197  for (unsigned i = 0, e = cb.V.size(); i != e; ++i) {
198    // Generate a report for this bug.
199    llvm::SmallString<512> buf;
200    llvm::raw_svector_ostream os(buf);
201    SourceRange range = GenName(os, cb.V[i].second,
202                                Eng.getContext().getSourceManager());
203    os << " is still referred to by the global variable '";
204    const VarRegion *VR = cast<VarRegion>(cb.V[i].first->getBaseRegion());
205    os << VR->getDecl()->getNameAsString()
206       << "' upon returning to the caller.  This will be a dangling reference";
207    RangedBugReport *report = new RangedBugReport(*BT_stackleak, os.str(), N);
208    if (range.isValid())
209      report->addRange(range);
210
211    Eng.getBugReporter().EmitReport(report);
212  }
213}
214
215void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
216  mgr.registerChecker<StackAddrEscapeChecker>();
217}
218