UnixAPIChecker.cpp revision 6bcf27bb9a4b5c3f79cb44c0e4654a6d7619ad89 
1//= UnixAPIChecker.h - Checks preconditions for various Unix APIs --*- 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 defines UnixAPIChecker, which is an assortment of checks on calls
11// to various, widely used UNIX/Posix functions.
12//
13//===----------------------------------------------------------------------===//
14
15#include "ClangSACheckers.h"
16#include "clang/Basic/TargetInfo.h"
17#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
18#include "clang/StaticAnalyzer/Core/Checker.h"
19#include "clang/StaticAnalyzer/Core/CheckerManager.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
21#include "llvm/ADT/Optional.h"
22#include "llvm/ADT/STLExtras.h"
23#include "llvm/ADT/SmallString.h"
24#include "llvm/ADT/StringSwitch.h"
25#include "llvm/Support/raw_ostream.h"
26#include <fcntl.h>
27
28using namespace clang;
29using namespace ento;
30
31namespace {
32class UnixAPIChecker : public Checker< check::PreStmt<CallExpr> > {
33  mutable std::unique_ptr<BugType> BT_open, BT_pthreadOnce, BT_mallocZero;
34  mutable Optional<uint64_t> Val_O_CREAT;
35
36public:
37  void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
38
39  void CheckOpen(CheckerContext &C, const CallExpr *CE) const;
40  void CheckPthreadOnce(CheckerContext &C, const CallExpr *CE) const;
41  void CheckCallocZero(CheckerContext &C, const CallExpr *CE) const;
42  void CheckMallocZero(CheckerContext &C, const CallExpr *CE) const;
43  void CheckReallocZero(CheckerContext &C, const CallExpr *CE) const;
44  void CheckReallocfZero(CheckerContext &C, const CallExpr *CE) const;
45  void CheckAllocaZero(CheckerContext &C, const CallExpr *CE) const;
46  void CheckVallocZero(CheckerContext &C, const CallExpr *CE) const;
47
48  typedef void (UnixAPIChecker::*SubChecker)(CheckerContext &,
49                                             const CallExpr *) const;
50private:
51  bool ReportZeroByteAllocation(CheckerContext &C,
52                                ProgramStateRef falseState,
53                                const Expr *arg,
54                                const char *fn_name) const;
55  void BasicAllocationCheck(CheckerContext &C,
56                            const CallExpr *CE,
57                            const unsigned numArgs,
58                            const unsigned sizeArg,
59                            const char *fn) const;
60  void LazyInitialize(std::unique_ptr<BugType> &BT, const char *name) const {
61    if (BT)
62      return;
63    BT.reset(new BugType(this, name, categories::UnixAPI));
64  }
65};
66} //end anonymous namespace
67
68//===----------------------------------------------------------------------===//
69// "open" (man 2 open)
70//===----------------------------------------------------------------------===//
71
72void UnixAPIChecker::CheckOpen(CheckerContext &C, const CallExpr *CE) const {
73  // The definition of O_CREAT is platform specific.  We need a better way
74  // of querying this information from the checking environment.
75  if (!Val_O_CREAT.hasValue()) {
76    if (C.getASTContext().getTargetInfo().getTriple().getVendor()
77                                                      == llvm::Triple::Apple)
78      Val_O_CREAT = 0x0200;
79    else {
80      // FIXME: We need a more general way of getting the O_CREAT value.
81      // We could possibly grovel through the preprocessor state, but
82      // that would require passing the Preprocessor object to the ExprEngine.
83      // See also: MallocChecker.cpp / M_ZERO.
84      return;
85    }
86  }
87
88  // Look at the 'oflags' argument for the O_CREAT flag.
89  ProgramStateRef state = C.getState();
90
91  if (CE->getNumArgs() < 2) {
92    // The frontend should issue a warning for this case, so this is a sanity
93    // check.
94    return;
95  }
96
97  // Now check if oflags has O_CREAT set.
98  const Expr *oflagsEx = CE->getArg(1);
99  const SVal V = state->getSVal(oflagsEx, C.getLocationContext());
100  if (!V.getAs<NonLoc>()) {
101    // The case where 'V' can be a location can only be due to a bad header,
102    // so in this case bail out.
103    return;
104  }
105  NonLoc oflags = V.castAs<NonLoc>();
106  NonLoc ocreateFlag = C.getSValBuilder()
107      .makeIntVal(Val_O_CREAT.getValue(), oflagsEx->getType()).castAs<NonLoc>();
108  SVal maskedFlagsUC = C.getSValBuilder().evalBinOpNN(state, BO_And,
109                                                      oflags, ocreateFlag,
110                                                      oflagsEx->getType());
111  if (maskedFlagsUC.isUnknownOrUndef())
112    return;
113  DefinedSVal maskedFlags = maskedFlagsUC.castAs<DefinedSVal>();
114
115  // Check if maskedFlags is non-zero.
116  ProgramStateRef trueState, falseState;
117  std::tie(trueState, falseState) = state->assume(maskedFlags);
118
119  // Only emit an error if the value of 'maskedFlags' is properly
120  // constrained;
121  if (!(trueState && !falseState))
122    return;
123
124  if (CE->getNumArgs() < 3) {
125    ExplodedNode *N = C.generateSink(trueState);
126    if (!N)
127      return;
128
129    LazyInitialize(BT_open, "Improper use of 'open'");
130
131    BugReport *report =
132      new BugReport(*BT_open,
133                            "Call to 'open' requires a third argument when "
134                            "the 'O_CREAT' flag is set", N);
135    report->addRange(oflagsEx->getSourceRange());
136    C.emitReport(report);
137  }
138}
139
140//===----------------------------------------------------------------------===//
141// pthread_once
142//===----------------------------------------------------------------------===//
143
144void UnixAPIChecker::CheckPthreadOnce(CheckerContext &C,
145                                      const CallExpr *CE) const {
146
147  // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker.
148  // They can possibly be refactored.
149
150  if (CE->getNumArgs() < 1)
151    return;
152
153  // Check if the first argument is stack allocated.  If so, issue a warning
154  // because that's likely to be bad news.
155  ProgramStateRef state = C.getState();
156  const MemRegion *R =
157    state->getSVal(CE->getArg(0), C.getLocationContext()).getAsRegion();
158  if (!R || !isa<StackSpaceRegion>(R->getMemorySpace()))
159    return;
160
161  ExplodedNode *N = C.generateSink(state);
162  if (!N)
163    return;
164
165  SmallString<256> S;
166  llvm::raw_svector_ostream os(S);
167  os << "Call to 'pthread_once' uses";
168  if (const VarRegion *VR = dyn_cast<VarRegion>(R))
169    os << " the local variable '" << VR->getDecl()->getName() << '\'';
170  else
171    os << " stack allocated memory";
172  os << " for the \"control\" value.  Using such transient memory for "
173  "the control value is potentially dangerous.";
174  if (isa<VarRegion>(R) && isa<StackLocalsSpaceRegion>(R->getMemorySpace()))
175    os << "  Perhaps you intended to declare the variable as 'static'?";
176
177  LazyInitialize(BT_pthreadOnce, "Improper use of 'pthread_once'");
178
179  BugReport *report = new BugReport(*BT_pthreadOnce, os.str(), N);
180  report->addRange(CE->getArg(0)->getSourceRange());
181  C.emitReport(report);
182}
183
184//===----------------------------------------------------------------------===//
185// "calloc", "malloc", "realloc", "reallocf", "alloca" and "valloc"
186// with allocation size 0
187//===----------------------------------------------------------------------===//
188// FIXME: Eventually these should be rolled into the MallocChecker, but right now
189// they're more basic and valuable for widespread use.
190
191// Returns true if we try to do a zero byte allocation, false otherwise.
192// Fills in trueState and falseState.
193static bool IsZeroByteAllocation(ProgramStateRef state,
194                                const SVal argVal,
195                                ProgramStateRef *trueState,
196                                ProgramStateRef *falseState) {
197  std::tie(*trueState, *falseState) =
198    state->assume(argVal.castAs<DefinedSVal>());
199
200  return (*falseState && !*trueState);
201}
202
203// Generates an error report, indicating that the function whose name is given
204// will perform a zero byte allocation.
205// Returns false if an error occurred, true otherwise.
206bool UnixAPIChecker::ReportZeroByteAllocation(CheckerContext &C,
207                                              ProgramStateRef falseState,
208                                              const Expr *arg,
209                                              const char *fn_name) const {
210  ExplodedNode *N = C.generateSink(falseState);
211  if (!N)
212    return false;
213
214  LazyInitialize(BT_mallocZero,
215                 "Undefined allocation of 0 bytes (CERT MEM04-C; CWE-131)");
216
217  SmallString<256> S;
218  llvm::raw_svector_ostream os(S);
219  os << "Call to '" << fn_name << "' has an allocation size of 0 bytes";
220  BugReport *report = new BugReport(*BT_mallocZero, os.str(), N);
221
222  report->addRange(arg->getSourceRange());
223  bugreporter::trackNullOrUndefValue(N, arg, *report);
224  C.emitReport(report);
225
226  return true;
227}
228
229// Does a basic check for 0-sized allocations suitable for most of the below
230// functions (modulo "calloc")
231void UnixAPIChecker::BasicAllocationCheck(CheckerContext &C,
232                                          const CallExpr *CE,
233                                          const unsigned numArgs,
234                                          const unsigned sizeArg,
235                                          const char *fn) const {
236  // Sanity check for the correct number of arguments
237  if (CE->getNumArgs() != numArgs)
238    return;
239
240  // Check if the allocation size is 0.
241  ProgramStateRef state = C.getState();
242  ProgramStateRef trueState = nullptr, falseState = nullptr;
243  const Expr *arg = CE->getArg(sizeArg);
244  SVal argVal = state->getSVal(arg, C.getLocationContext());
245
246  if (argVal.isUnknownOrUndef())
247    return;
248
249  // Is the value perfectly constrained to zero?
250  if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
251    (void) ReportZeroByteAllocation(C, falseState, arg, fn);
252    return;
253  }
254  // Assume the value is non-zero going forward.
255  assert(trueState);
256  if (trueState != state)
257    C.addTransition(trueState);
258}
259
260void UnixAPIChecker::CheckCallocZero(CheckerContext &C,
261                                     const CallExpr *CE) const {
262  unsigned int nArgs = CE->getNumArgs();
263  if (nArgs != 2)
264    return;
265
266  ProgramStateRef state = C.getState();
267  ProgramStateRef trueState = nullptr, falseState = nullptr;
268
269  unsigned int i;
270  for (i = 0; i < nArgs; i++) {
271    const Expr *arg = CE->getArg(i);
272    SVal argVal = state->getSVal(arg, C.getLocationContext());
273    if (argVal.isUnknownOrUndef()) {
274      if (i == 0)
275        continue;
276      else
277        return;
278    }
279
280    if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
281      if (ReportZeroByteAllocation(C, falseState, arg, "calloc"))
282        return;
283      else if (i == 0)
284        continue;
285      else
286        return;
287    }
288  }
289
290  // Assume the value is non-zero going forward.
291  assert(trueState);
292  if (trueState != state)
293    C.addTransition(trueState);
294}
295
296void UnixAPIChecker::CheckMallocZero(CheckerContext &C,
297                                     const CallExpr *CE) const {
298  BasicAllocationCheck(C, CE, 1, 0, "malloc");
299}
300
301void UnixAPIChecker::CheckReallocZero(CheckerContext &C,
302                                      const CallExpr *CE) const {
303  BasicAllocationCheck(C, CE, 2, 1, "realloc");
304}
305
306void UnixAPIChecker::CheckReallocfZero(CheckerContext &C,
307                                       const CallExpr *CE) const {
308  BasicAllocationCheck(C, CE, 2, 1, "reallocf");
309}
310
311void UnixAPIChecker::CheckAllocaZero(CheckerContext &C,
312                                     const CallExpr *CE) const {
313  BasicAllocationCheck(C, CE, 1, 0, "alloca");
314}
315
316void UnixAPIChecker::CheckVallocZero(CheckerContext &C,
317                                     const CallExpr *CE) const {
318  BasicAllocationCheck(C, CE, 1, 0, "valloc");
319}
320
321
322//===----------------------------------------------------------------------===//
323// Central dispatch function.
324//===----------------------------------------------------------------------===//
325
326void UnixAPIChecker::checkPreStmt(const CallExpr *CE,
327                                  CheckerContext &C) const {
328  const FunctionDecl *FD = C.getCalleeDecl(CE);
329  if (!FD || FD->getKind() != Decl::Function)
330    return;
331
332  StringRef FName = C.getCalleeName(FD);
333  if (FName.empty())
334    return;
335
336  SubChecker SC =
337    llvm::StringSwitch<SubChecker>(FName)
338      .Case("open", &UnixAPIChecker::CheckOpen)
339      .Case("pthread_once", &UnixAPIChecker::CheckPthreadOnce)
340      .Case("calloc", &UnixAPIChecker::CheckCallocZero)
341      .Case("malloc", &UnixAPIChecker::CheckMallocZero)
342      .Case("realloc", &UnixAPIChecker::CheckReallocZero)
343      .Case("reallocf", &UnixAPIChecker::CheckReallocfZero)
344      .Cases("alloca", "__builtin_alloca", &UnixAPIChecker::CheckAllocaZero)
345      .Case("valloc", &UnixAPIChecker::CheckVallocZero)
346      .Default(nullptr);
347
348  if (SC)
349    (this->*SC)(C, CE);
350}
351
352//===----------------------------------------------------------------------===//
353// Registration.
354//===----------------------------------------------------------------------===//
355
356void ento::registerUnixAPIChecker(CheckerManager &mgr) {
357  mgr.registerChecker<UnixAPIChecker>();
358}
359