UnixAPIChecker.cpp revision a1f81bb0e55749a1414b1b5124bb83b9052ff2ac 
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/SmallString.h"
23#include "llvm/ADT/STLExtras.h"
24#include "llvm/ADT/StringSwitch.h"
25#include <fcntl.h>
26
27using namespace clang;
28using namespace ento;
29using llvm::Optional;
30
31namespace {
32class UnixAPIChecker : public Checker< check::PreStmt<CallExpr> > {
33  mutable OwningPtr<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 CheckAllocaZero(CheckerContext &C, const CallExpr *CE) const;
45  void CheckVallocZero(CheckerContext &C, const CallExpr *CE) const;
46
47  typedef void (UnixAPIChecker::*SubChecker)(CheckerContext &,
48                                             const CallExpr *) const;
49private:
50  bool ReportZeroByteAllocation(CheckerContext &C,
51                                ProgramStateRef falseState,
52                                const Expr *arg,
53                                const char *fn_name) const;
54  void BasicAllocationCheck(CheckerContext &C,
55                            const CallExpr *CE,
56                            const unsigned numArgs,
57                            const unsigned sizeArg,
58                            const char *fn) const;
59};
60} //end anonymous namespace
61
62//===----------------------------------------------------------------------===//
63// Utility functions.
64//===----------------------------------------------------------------------===//
65
66static inline void LazyInitialize(OwningPtr<BugType> &BT,
67                                  const char *name) {
68  if (BT)
69    return;
70  BT.reset(new BugType(name, categories::UnixAPI));
71}
72
73//===----------------------------------------------------------------------===//
74// "open" (man 2 open)
75//===----------------------------------------------------------------------===//
76
77void UnixAPIChecker::CheckOpen(CheckerContext &C, const CallExpr *CE) const {
78  // The definition of O_CREAT is platform specific.  We need a better way
79  // of querying this information from the checking environment.
80  if (!Val_O_CREAT.hasValue()) {
81    if (C.getASTContext().getTargetInfo().getTriple().getVendor()
82                                                      == llvm::Triple::Apple)
83      Val_O_CREAT = 0x0200;
84    else {
85      // FIXME: We need a more general way of getting the O_CREAT value.
86      // We could possibly grovel through the preprocessor state, but
87      // that would require passing the Preprocessor object to the ExprEngine.
88      return;
89    }
90  }
91
92  // Look at the 'oflags' argument for the O_CREAT flag.
93  ProgramStateRef state = C.getState();
94
95  if (CE->getNumArgs() < 2) {
96    // The frontend should issue a warning for this case, so this is a sanity
97    // check.
98    return;
99  }
100
101  // Now check if oflags has O_CREAT set.
102  const Expr *oflagsEx = CE->getArg(1);
103  const SVal V = state->getSVal(oflagsEx, C.getLocationContext());
104  if (!isa<NonLoc>(V)) {
105    // The case where 'V' can be a location can only be due to a bad header,
106    // so in this case bail out.
107    return;
108  }
109  NonLoc oflags = cast<NonLoc>(V);
110  NonLoc ocreateFlag =
111    cast<NonLoc>(C.getSValBuilder().makeIntVal(Val_O_CREAT.getValue(),
112                                                oflagsEx->getType()));
113  SVal maskedFlagsUC = C.getSValBuilder().evalBinOpNN(state, BO_And,
114                                                      oflags, ocreateFlag,
115                                                      oflagsEx->getType());
116  if (maskedFlagsUC.isUnknownOrUndef())
117    return;
118  DefinedSVal maskedFlags = cast<DefinedSVal>(maskedFlagsUC);
119
120  // Check if maskedFlags is non-zero.
121  ProgramStateRef trueState, falseState;
122  llvm::tie(trueState, falseState) = state->assume(maskedFlags);
123
124  // Only emit an error if the value of 'maskedFlags' is properly
125  // constrained;
126  if (!(trueState && !falseState))
127    return;
128
129  if (CE->getNumArgs() < 3) {
130    ExplodedNode *N = C.generateSink(trueState);
131    if (!N)
132      return;
133
134    LazyInitialize(BT_open, "Improper use of 'open'");
135
136    BugReport *report =
137      new BugReport(*BT_open,
138                            "Call to 'open' requires a third argument when "
139                            "the 'O_CREAT' flag is set", N);
140    report->addRange(oflagsEx->getSourceRange());
141    C.EmitReport(report);
142  }
143}
144
145//===----------------------------------------------------------------------===//
146// pthread_once
147//===----------------------------------------------------------------------===//
148
149void UnixAPIChecker::CheckPthreadOnce(CheckerContext &C,
150                                      const CallExpr *CE) const {
151
152  // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker.
153  // They can possibly be refactored.
154
155  if (CE->getNumArgs() < 1)
156    return;
157
158  // Check if the first argument is stack allocated.  If so, issue a warning
159  // because that's likely to be bad news.
160  ProgramStateRef state = C.getState();
161  const MemRegion *R =
162    state->getSVal(CE->getArg(0), C.getLocationContext()).getAsRegion();
163  if (!R || !isa<StackSpaceRegion>(R->getMemorySpace()))
164    return;
165
166  ExplodedNode *N = C.generateSink(state);
167  if (!N)
168    return;
169
170  SmallString<256> S;
171  llvm::raw_svector_ostream os(S);
172  os << "Call to 'pthread_once' uses";
173  if (const VarRegion *VR = dyn_cast<VarRegion>(R))
174    os << " the local variable '" << VR->getDecl()->getName() << '\'';
175  else
176    os << " stack allocated memory";
177  os << " for the \"control\" value.  Using such transient memory for "
178  "the control value is potentially dangerous.";
179  if (isa<VarRegion>(R) && isa<StackLocalsSpaceRegion>(R->getMemorySpace()))
180    os << "  Perhaps you intended to declare the variable as 'static'?";
181
182  LazyInitialize(BT_pthreadOnce, "Improper use of 'pthread_once'");
183
184  BugReport *report = new BugReport(*BT_pthreadOnce, os.str(), N);
185  report->addRange(CE->getArg(0)->getSourceRange());
186  C.EmitReport(report);
187}
188
189//===----------------------------------------------------------------------===//
190// "calloc", "malloc", "realloc", "alloca" and "valloc" with allocation size 0
191//===----------------------------------------------------------------------===//
192// FIXME: Eventually these should be rolled into the MallocChecker, but right now
193// they're more basic and valuable for widespread use.
194
195// Returns true if we try to do a zero byte allocation, false otherwise.
196// Fills in trueState and falseState.
197static bool IsZeroByteAllocation(ProgramStateRef state,
198                                const SVal argVal,
199                                ProgramStateRef *trueState,
200                                ProgramStateRef *falseState) {
201  llvm::tie(*trueState, *falseState) =
202    state->assume(cast<DefinedSVal>(argVal));
203
204  return (*falseState && !*trueState);
205}
206
207// Generates an error report, indicating that the function whose name is given
208// will perform a zero byte allocation.
209// Returns false if an error occured, true otherwise.
210bool UnixAPIChecker::ReportZeroByteAllocation(CheckerContext &C,
211                                              ProgramStateRef falseState,
212                                              const Expr *arg,
213                                              const char *fn_name) const {
214  ExplodedNode *N = C.generateSink(falseState);
215  if (!N)
216    return false;
217
218  LazyInitialize(BT_mallocZero,
219    "Undefined allocation of 0 bytes (CERT MEM04-C; CWE-131)");
220
221  SmallString<256> S;
222  llvm::raw_svector_ostream os(S);
223  os << "Call to '" << fn_name << "' has an allocation size of 0 bytes";
224  BugReport *report = new BugReport(*BT_mallocZero, os.str(), N);
225
226  report->addRange(arg->getSourceRange());
227  bugreporter::trackNullOrUndefValue(N, arg, *report);
228  C.EmitReport(report);
229
230  return true;
231}
232
233// Does a basic check for 0-sized allocations suitable for most of the below
234// functions (modulo "calloc")
235void UnixAPIChecker::BasicAllocationCheck(CheckerContext &C,
236                                          const CallExpr *CE,
237                                          const unsigned numArgs,
238                                          const unsigned sizeArg,
239                                          const char *fn) const {
240  // Sanity check for the correct number of arguments
241  if (CE->getNumArgs() != numArgs)
242    return;
243
244  // Check if the allocation size is 0.
245  ProgramStateRef state = C.getState();
246  ProgramStateRef trueState = NULL, falseState = NULL;
247  const Expr *arg = CE->getArg(sizeArg);
248  SVal argVal = state->getSVal(arg, C.getLocationContext());
249
250  if (argVal.isUnknownOrUndef())
251    return;
252
253  // Is the value perfectly constrained to zero?
254  if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
255    (void) ReportZeroByteAllocation(C, falseState, arg, fn);
256    return;
257  }
258  // Assume the value is non-zero going forward.
259  assert(trueState);
260  if (trueState != state)
261    C.addTransition(trueState);
262}
263
264void UnixAPIChecker::CheckCallocZero(CheckerContext &C,
265                                     const CallExpr *CE) const {
266  unsigned int nArgs = CE->getNumArgs();
267  if (nArgs != 2)
268    return;
269
270  ProgramStateRef state = C.getState();
271  ProgramStateRef trueState = NULL, falseState = NULL;
272
273  unsigned int i;
274  for (i = 0; i < nArgs; i++) {
275    const Expr *arg = CE->getArg(i);
276    SVal argVal = state->getSVal(arg, C.getLocationContext());
277    if (argVal.isUnknownOrUndef()) {
278      if (i == 0)
279        continue;
280      else
281        return;
282    }
283
284    if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
285      if (ReportZeroByteAllocation(C, falseState, arg, "calloc"))
286        return;
287      else if (i == 0)
288        continue;
289      else
290        return;
291    }
292  }
293
294  // Assume the value is non-zero going forward.
295  assert(trueState);
296  if (trueState != state)
297    C.addTransition(trueState);
298}
299
300void UnixAPIChecker::CheckMallocZero(CheckerContext &C,
301                                     const CallExpr *CE) const {
302  BasicAllocationCheck(C, CE, 1, 0, "malloc");
303}
304
305void UnixAPIChecker::CheckReallocZero(CheckerContext &C,
306                                      const CallExpr *CE) const {
307  BasicAllocationCheck(C, CE, 2, 1, "realloc");
308}
309
310void UnixAPIChecker::CheckAllocaZero(CheckerContext &C,
311                                     const CallExpr *CE) const {
312  BasicAllocationCheck(C, CE, 1, 0, "alloca");
313}
314
315void UnixAPIChecker::CheckVallocZero(CheckerContext &C,
316                                     const CallExpr *CE) const {
317  BasicAllocationCheck(C, CE, 1, 0, "valloc");
318}
319
320
321//===----------------------------------------------------------------------===//
322// Central dispatch function.
323//===----------------------------------------------------------------------===//
324
325void UnixAPIChecker::checkPreStmt(const CallExpr *CE,
326                                  CheckerContext &C) const {
327  const FunctionDecl *FD = C.getCalleeDecl(CE);
328  if (!FD || FD->getKind() != Decl::Function)
329    return;
330
331  StringRef FName = C.getCalleeName(FD);
332  if (FName.empty())
333    return;
334
335  SubChecker SC =
336    llvm::StringSwitch<SubChecker>(FName)
337      .Case("open", &UnixAPIChecker::CheckOpen)
338      .Case("pthread_once", &UnixAPIChecker::CheckPthreadOnce)
339      .Case("calloc", &UnixAPIChecker::CheckCallocZero)
340      .Case("malloc", &UnixAPIChecker::CheckMallocZero)
341      .Case("realloc", &UnixAPIChecker::CheckReallocZero)
342      .Cases("alloca", "__builtin_alloca", &UnixAPIChecker::CheckAllocaZero)
343      .Case("valloc", &UnixAPIChecker::CheckVallocZero)
344      .Default(NULL);
345
346  if (SC)
347    (this->*SC)(C, CE);
348}
349
350//===----------------------------------------------------------------------===//
351// Registration.
352//===----------------------------------------------------------------------===//
353
354void ento::registerUnixAPIChecker(CheckerManager &mgr) {
355  mgr.registerChecker<UnixAPIChecker>();
356}
357