UnixAPIChecker.cpp revision 8bef8238181a30e52dea380789a7e2d760eac532 
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/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/Basic/TargetInfo.h"
21#include "llvm/ADT/Optional.h"
22#include "llvm/ADT/StringSwitch.h"
23#include <fcntl.h>
24
25using namespace clang;
26using namespace ento;
27using llvm::Optional;
28
29namespace {
30class UnixAPIChecker : public Checker< check::PreStmt<CallExpr> > {
31  mutable llvm::OwningPtr<BugType> BT_open, BT_pthreadOnce, BT_mallocZero;
32  mutable Optional<uint64_t> Val_O_CREAT;
33
34public:
35  void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
36
37  void CheckOpen(CheckerContext &C, const CallExpr *CE) const;
38  void CheckPthreadOnce(CheckerContext &C, const CallExpr *CE) const;
39  void CheckCallocZero(CheckerContext &C, const CallExpr *CE) const;
40  void CheckMallocZero(CheckerContext &C, const CallExpr *CE) const;
41  void CheckReallocZero(CheckerContext &C, const CallExpr *CE) const;
42  void CheckAllocaZero(CheckerContext &C, const CallExpr *CE) const;
43  void CheckVallocZero(CheckerContext &C, const CallExpr *CE) const;
44
45  typedef void (UnixAPIChecker::*SubChecker)(CheckerContext &,
46                                             const CallExpr *) const;
47private:
48  bool ReportZeroByteAllocation(CheckerContext &C,
49                                ProgramStateRef falseState,
50                                const Expr *arg,
51                                const char *fn_name) const;
52  void BasicAllocationCheck(CheckerContext &C,
53                            const CallExpr *CE,
54                            const unsigned numArgs,
55                            const unsigned sizeArg,
56                            const char *fn) const;
57};
58} //end anonymous namespace
59
60//===----------------------------------------------------------------------===//
61// Utility functions.
62//===----------------------------------------------------------------------===//
63
64static inline void LazyInitialize(llvm::OwningPtr<BugType> &BT,
65                                  const char *name) {
66  if (BT)
67    return;
68  BT.reset(new BugType(name, "Unix API"));
69}
70
71//===----------------------------------------------------------------------===//
72// "open" (man 2 open)
73//===----------------------------------------------------------------------===//
74
75void UnixAPIChecker::CheckOpen(CheckerContext &C, const CallExpr *CE) const {
76  // The definition of O_CREAT is platform specific.  We need a better way
77  // of querying this information from the checking environment.
78  if (!Val_O_CREAT.hasValue()) {
79    if (C.getASTContext().getTargetInfo().getTriple().getVendor()
80                                                      == llvm::Triple::Apple)
81      Val_O_CREAT = 0x0200;
82    else {
83      // FIXME: We need a more general way of getting the O_CREAT value.
84      // We could possibly grovel through the preprocessor state, but
85      // that would require passing the Preprocessor object to the ExprEngine.
86      return;
87    }
88  }
89
90  // Look at the 'oflags' argument for the O_CREAT flag.
91  ProgramStateRef state = C.getState();
92
93  if (CE->getNumArgs() < 2) {
94    // The frontend should issue a warning for this case, so this is a sanity
95    // check.
96    return;
97  }
98
99  // Now check if oflags has O_CREAT set.
100  const Expr *oflagsEx = CE->getArg(1);
101  const SVal V = state->getSVal(oflagsEx, C.getLocationContext());
102  if (!isa<NonLoc>(V)) {
103    // The case where 'V' can be a location can only be due to a bad header,
104    // so in this case bail out.
105    return;
106  }
107  NonLoc oflags = cast<NonLoc>(V);
108  NonLoc ocreateFlag =
109    cast<NonLoc>(C.getSValBuilder().makeIntVal(Val_O_CREAT.getValue(),
110                                                oflagsEx->getType()));
111  SVal maskedFlagsUC = C.getSValBuilder().evalBinOpNN(state, BO_And,
112                                                      oflags, ocreateFlag,
113                                                      oflagsEx->getType());
114  if (maskedFlagsUC.isUnknownOrUndef())
115    return;
116  DefinedSVal maskedFlags = cast<DefinedSVal>(maskedFlagsUC);
117
118  // Check if maskedFlags is non-zero.
119  ProgramStateRef trueState, falseState;
120  llvm::tie(trueState, falseState) = state->assume(maskedFlags);
121
122  // Only emit an error if the value of 'maskedFlags' is properly
123  // constrained;
124  if (!(trueState && !falseState))
125    return;
126
127  if (CE->getNumArgs() < 3) {
128    ExplodedNode *N = C.generateSink(trueState);
129    if (!N)
130      return;
131
132    LazyInitialize(BT_open, "Improper use of 'open'");
133
134    BugReport *report =
135      new BugReport(*BT_open,
136                            "Call to 'open' requires a third argument when "
137                            "the 'O_CREAT' flag is set", N);
138    report->addRange(oflagsEx->getSourceRange());
139    C.EmitReport(report);
140  }
141}
142
143//===----------------------------------------------------------------------===//
144// pthread_once
145//===----------------------------------------------------------------------===//
146
147void UnixAPIChecker::CheckPthreadOnce(CheckerContext &C,
148                                      const CallExpr *CE) const {
149
150  // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker.
151  // They can possibly be refactored.
152
153  if (CE->getNumArgs() < 1)
154    return;
155
156  // Check if the first argument is stack allocated.  If so, issue a warning
157  // because that's likely to be bad news.
158  ProgramStateRef state = C.getState();
159  const MemRegion *R =
160    state->getSVal(CE->getArg(0), C.getLocationContext()).getAsRegion();
161  if (!R || !isa<StackSpaceRegion>(R->getMemorySpace()))
162    return;
163
164  ExplodedNode *N = C.generateSink(state);
165  if (!N)
166    return;
167
168  llvm::SmallString<256> S;
169  llvm::raw_svector_ostream os(S);
170  os << "Call to 'pthread_once' uses";
171  if (const VarRegion *VR = dyn_cast<VarRegion>(R))
172    os << " the local variable '" << VR->getDecl()->getName() << '\'';
173  else
174    os << " stack allocated memory";
175  os << " for the \"control\" value.  Using such transient memory for "
176  "the control value is potentially dangerous.";
177  if (isa<VarRegion>(R) && isa<StackLocalsSpaceRegion>(R->getMemorySpace()))
178    os << "  Perhaps you intended to declare the variable as 'static'?";
179
180  LazyInitialize(BT_pthreadOnce, "Improper use of 'pthread_once'");
181
182  BugReport *report = new BugReport(*BT_pthreadOnce, os.str(), N);
183  report->addRange(CE->getArg(0)->getSourceRange());
184  C.EmitReport(report);
185}
186
187//===----------------------------------------------------------------------===//
188// "calloc", "malloc", "realloc", "alloca" and "valloc" with allocation size 0
189//===----------------------------------------------------------------------===//
190// FIXME: Eventually these should be rolled into the MallocChecker, but right now
191// they're more basic and valuable for widespread use.
192
193// Returns true if we try to do a zero byte allocation, false otherwise.
194// Fills in trueState and falseState.
195static bool IsZeroByteAllocation(ProgramStateRef state,
196                                const SVal argVal,
197                                ProgramStateRef *trueState,
198                                ProgramStateRef *falseState) {
199  llvm::tie(*trueState, *falseState) =
200    state->assume(cast<DefinedSVal>(argVal));
201
202  return (*falseState && !*trueState);
203}
204
205// Generates an error report, indicating that the function whose name is given
206// will perform a zero byte allocation.
207// Returns false if an error occured, true otherwise.
208bool UnixAPIChecker::ReportZeroByteAllocation(CheckerContext &C,
209                                              ProgramStateRef falseState,
210                                              const Expr *arg,
211                                              const char *fn_name) const {
212  ExplodedNode *N = C.generateSink(falseState);
213  if (!N)
214    return false;
215
216  LazyInitialize(BT_mallocZero,
217    "Undefined allocation of 0 bytes (CERT MEM04-C; CWE-131)");
218
219  llvm::SmallString<256> S;
220  llvm::raw_svector_ostream os(S);
221  os << "Call to '" << fn_name << "' has an allocation size of 0 bytes";
222  BugReport *report = new BugReport(*BT_mallocZero, os.str(), N);
223
224  report->addRange(arg->getSourceRange());
225  report->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N, arg));
226  C.EmitReport(report);
227
228  return true;
229}
230
231// Does a basic check for 0-sized allocations suitable for most of the below
232// functions (modulo "calloc")
233void UnixAPIChecker::BasicAllocationCheck(CheckerContext &C,
234                                          const CallExpr *CE,
235                                          const unsigned numArgs,
236                                          const unsigned sizeArg,
237                                          const char *fn) const {
238  // Sanity check for the correct number of arguments
239  if (CE->getNumArgs() != numArgs)
240    return;
241
242  // Check if the allocation size is 0.
243  ProgramStateRef state = C.getState();
244  ProgramStateRef trueState = NULL, falseState = NULL;
245  const Expr *arg = CE->getArg(sizeArg);
246  SVal argVal = state->getSVal(arg, C.getLocationContext());
247
248  if (argVal.isUnknownOrUndef())
249    return;
250
251  // Is the value perfectly constrained to zero?
252  if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
253    (void) ReportZeroByteAllocation(C, falseState, arg, fn);
254    return;
255  }
256  // Assume the the value is non-zero going forward.
257  assert(trueState);
258  if (trueState != state)
259    C.addTransition(trueState);
260}
261
262void UnixAPIChecker::CheckCallocZero(CheckerContext &C,
263                                     const CallExpr *CE) const {
264  unsigned int nArgs = CE->getNumArgs();
265  if (nArgs != 2)
266    return;
267
268  ProgramStateRef state = C.getState();
269  ProgramStateRef trueState = NULL, falseState = NULL;
270
271  unsigned int i;
272  for (i = 0; i < nArgs; i++) {
273    const Expr *arg = CE->getArg(i);
274    SVal argVal = state->getSVal(arg, C.getLocationContext());
275    if (argVal.isUnknownOrUndef()) {
276      if (i == 0)
277        continue;
278      else
279        return;
280    }
281
282    if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
283      if (ReportZeroByteAllocation(C, falseState, arg, "calloc"))
284        return;
285      else if (i == 0)
286        continue;
287      else
288        return;
289    }
290  }
291
292  // Assume the the value is non-zero going forward.
293  assert(trueState);
294  if (trueState != state)
295    C.addTransition(trueState);
296}
297
298void UnixAPIChecker::CheckMallocZero(CheckerContext &C,
299                                     const CallExpr *CE) const {
300  BasicAllocationCheck(C, CE, 1, 0, "malloc");
301}
302
303void UnixAPIChecker::CheckReallocZero(CheckerContext &C,
304                                      const CallExpr *CE) const {
305  BasicAllocationCheck(C, CE, 2, 1, "realloc");
306}
307
308void UnixAPIChecker::CheckAllocaZero(CheckerContext &C,
309                                     const CallExpr *CE) const {
310  BasicAllocationCheck(C, CE, 1, 0, "alloca");
311}
312
313void UnixAPIChecker::CheckVallocZero(CheckerContext &C,
314                                     const CallExpr *CE) const {
315  BasicAllocationCheck(C, CE, 1, 0, "valloc");
316}
317
318
319//===----------------------------------------------------------------------===//
320// Central dispatch function.
321//===----------------------------------------------------------------------===//
322
323void UnixAPIChecker::checkPreStmt(const CallExpr *CE,
324                                  CheckerContext &C) const {
325  StringRef FName = C.getCalleeName(CE);
326  if (FName.empty())
327    return;
328
329  SubChecker SC =
330    llvm::StringSwitch<SubChecker>(FName)
331      .Case("open", &UnixAPIChecker::CheckOpen)
332      .Case("pthread_once", &UnixAPIChecker::CheckPthreadOnce)
333      .Case("calloc", &UnixAPIChecker::CheckCallocZero)
334      .Case("malloc", &UnixAPIChecker::CheckMallocZero)
335      .Case("realloc", &UnixAPIChecker::CheckReallocZero)
336      .Cases("alloca", "__builtin_alloca", &UnixAPIChecker::CheckAllocaZero)
337      .Case("valloc", &UnixAPIChecker::CheckVallocZero)
338      .Default(NULL);
339
340  if (SC)
341    (this->*SC)(C, CE);
342}
343
344//===----------------------------------------------------------------------===//
345// Registration.
346//===----------------------------------------------------------------------===//
347
348void ento::registerUnixAPIChecker(CheckerManager &mgr) {
349  mgr.registerChecker<UnixAPIChecker>();
350}
351