UnixAPIChecker.cpp revision 50bbc165b063155cc23c360deb7b865502e068e2 
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 CheckMallocZero(CheckerContext &C, const CallExpr *CE) const;
40
41  typedef void (UnixAPIChecker::*SubChecker)(CheckerContext &,
42                                             const CallExpr *) const;
43};
44} //end anonymous namespace
45
46//===----------------------------------------------------------------------===//
47// Utility functions.
48//===----------------------------------------------------------------------===//
49
50static inline void LazyInitialize(llvm::OwningPtr<BugType> &BT,
51                                  const char *name) {
52  if (BT)
53    return;
54  BT.reset(new BugType(name, "Unix API"));
55}
56
57//===----------------------------------------------------------------------===//
58// "open" (man 2 open)
59//===----------------------------------------------------------------------===//
60
61void UnixAPIChecker::CheckOpen(CheckerContext &C, const CallExpr *CE) const {
62  // The definition of O_CREAT is platform specific.  We need a better way
63  // of querying this information from the checking environment.
64  if (!Val_O_CREAT.hasValue()) {
65    if (C.getASTContext().Target.getTriple().getVendor() == llvm::Triple::Apple)
66      Val_O_CREAT = 0x0200;
67    else {
68      // FIXME: We need a more general way of getting the O_CREAT value.
69      // We could possibly grovel through the preprocessor state, but
70      // that would require passing the Preprocessor object to the ExprEngine.
71      return;
72    }
73  }
74
75  // Look at the 'oflags' argument for the O_CREAT flag.
76  const ProgramState *state = C.getState();
77
78  if (CE->getNumArgs() < 2) {
79    // The frontend should issue a warning for this case, so this is a sanity
80    // check.
81    return;
82  }
83
84  // Now check if oflags has O_CREAT set.
85  const Expr *oflagsEx = CE->getArg(1);
86  const SVal V = state->getSVal(oflagsEx);
87  if (!isa<NonLoc>(V)) {
88    // The case where 'V' can be a location can only be due to a bad header,
89    // so in this case bail out.
90    return;
91  }
92  NonLoc oflags = cast<NonLoc>(V);
93  NonLoc ocreateFlag =
94    cast<NonLoc>(C.getSValBuilder().makeIntVal(Val_O_CREAT.getValue(),
95                                                oflagsEx->getType()));
96  SVal maskedFlagsUC = C.getSValBuilder().evalBinOpNN(state, BO_And,
97                                                      oflags, ocreateFlag,
98                                                      oflagsEx->getType());
99  if (maskedFlagsUC.isUnknownOrUndef())
100    return;
101  DefinedSVal maskedFlags = cast<DefinedSVal>(maskedFlagsUC);
102
103  // Check if maskedFlags is non-zero.
104  const ProgramState *trueState, *falseState;
105  llvm::tie(trueState, falseState) = state->assume(maskedFlags);
106
107  // Only emit an error if the value of 'maskedFlags' is properly
108  // constrained;
109  if (!(trueState && !falseState))
110    return;
111
112  if (CE->getNumArgs() < 3) {
113    ExplodedNode *N = C.generateSink(trueState);
114    if (!N)
115      return;
116
117    LazyInitialize(BT_open, "Improper use of 'open'");
118
119    BugReport *report =
120      new BugReport(*BT_open,
121                            "Call to 'open' requires a third argument when "
122                            "the 'O_CREAT' flag is set", N);
123    report->addRange(oflagsEx->getSourceRange());
124    C.EmitReport(report);
125  }
126}
127
128//===----------------------------------------------------------------------===//
129// pthread_once
130//===----------------------------------------------------------------------===//
131
132void UnixAPIChecker::CheckPthreadOnce(CheckerContext &C,
133                                      const CallExpr *CE) const {
134
135  // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker.
136  // They can possibly be refactored.
137
138  if (CE->getNumArgs() < 1)
139    return;
140
141  // Check if the first argument is stack allocated.  If so, issue a warning
142  // because that's likely to be bad news.
143  const ProgramState *state = C.getState();
144  const MemRegion *R = state->getSVal(CE->getArg(0)).getAsRegion();
145  if (!R || !isa<StackSpaceRegion>(R->getMemorySpace()))
146    return;
147
148  ExplodedNode *N = C.generateSink(state);
149  if (!N)
150    return;
151
152  llvm::SmallString<256> S;
153  llvm::raw_svector_ostream os(S);
154  os << "Call to 'pthread_once' uses";
155  if (const VarRegion *VR = dyn_cast<VarRegion>(R))
156    os << " the local variable '" << VR->getDecl()->getName() << '\'';
157  else
158    os << " stack allocated memory";
159  os << " for the \"control\" value.  Using such transient memory for "
160  "the control value is potentially dangerous.";
161  if (isa<VarRegion>(R) && isa<StackLocalsSpaceRegion>(R->getMemorySpace()))
162    os << "  Perhaps you intended to declare the variable as 'static'?";
163
164  LazyInitialize(BT_pthreadOnce, "Improper use of 'pthread_once'");
165
166  BugReport *report = new BugReport(*BT_pthreadOnce, os.str(), N);
167  report->addRange(CE->getArg(0)->getSourceRange());
168  C.EmitReport(report);
169}
170
171//===----------------------------------------------------------------------===//
172// "malloc" with allocation size 0
173//===----------------------------------------------------------------------===//
174
175// FIXME: Eventually this should be rolled into the MallocChecker, but this
176// check is more basic and is valuable for widespread use.
177void UnixAPIChecker::CheckMallocZero(CheckerContext &C,
178                                     const CallExpr *CE) const {
179
180  // Sanity check that malloc takes one argument.
181  if (CE->getNumArgs() != 1)
182    return;
183
184  // Check if the allocation size is 0.
185  const ProgramState *state = C.getState();
186  SVal argVal = state->getSVal(CE->getArg(0));
187
188  if (argVal.isUnknownOrUndef())
189    return;
190
191  const ProgramState *trueState, *falseState;
192  llvm::tie(trueState, falseState) = state->assume(cast<DefinedSVal>(argVal));
193
194  // Is the value perfectly constrained to zero?
195  if (falseState && !trueState) {
196    ExplodedNode *N = C.generateSink(falseState);
197    if (!N)
198      return;
199
200    // FIXME: Add reference to CERT advisory, and/or C99 standard in bug
201    // output.
202
203    LazyInitialize(BT_mallocZero, "Undefined allocation of 0 bytes");
204
205    BugReport *report =
206      new BugReport(*BT_mallocZero, "Call to 'malloc' has an allocation"
207                                            " size of 0 bytes", N);
208    report->addRange(CE->getArg(0)->getSourceRange());
209    report->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
210                                                                CE->getArg(0)));
211    C.EmitReport(report);
212    return;
213  }
214  // Assume the the value is non-zero going forward.
215  assert(trueState);
216  if (trueState != state) {
217    C.addTransition(trueState);
218  }
219}
220
221//===----------------------------------------------------------------------===//
222// Central dispatch function.
223//===----------------------------------------------------------------------===//
224
225void UnixAPIChecker::checkPreStmt(const CallExpr *CE, CheckerContext &C) const {
226  // Get the callee.  All the functions we care about are C functions
227  // with simple identifiers.
228  const ProgramState *state = C.getState();
229  const Expr *Callee = CE->getCallee();
230  const FunctionDecl *Fn = state->getSVal(Callee).getAsFunctionDecl();
231
232  if (!Fn)
233    return;
234
235  const IdentifierInfo *FI = Fn->getIdentifier();
236  if (!FI)
237    return;
238
239  SubChecker SC =
240    llvm::StringSwitch<SubChecker>(FI->getName())
241      .Case("open", &UnixAPIChecker::CheckOpen)
242      .Case("pthread_once", &UnixAPIChecker::CheckPthreadOnce)
243      .Case("malloc", &UnixAPIChecker::CheckMallocZero)
244      .Default(NULL);
245
246  if (SC)
247    (this->*SC)(C, CE);
248}
249
250//===----------------------------------------------------------------------===//
251// Registration.
252//===----------------------------------------------------------------------===//
253
254void ento::registerUnixAPIChecker(CheckerManager &mgr) {
255  mgr.registerChecker<UnixAPIChecker>();
256}
257