UnixAPIChecker.cpp revision f5d6176554eda96ac4097a0a1e0852250cadfb9a 
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().getTargetInfo().getTriple().getVendor()
66                                                      == llvm::Triple::Apple)
67      Val_O_CREAT = 0x0200;
68    else {
69      // FIXME: We need a more general way of getting the O_CREAT value.
70      // We could possibly grovel through the preprocessor state, but
71      // that would require passing the Preprocessor object to the ExprEngine.
72      return;
73    }
74  }
75
76  // Look at the 'oflags' argument for the O_CREAT flag.
77  const ProgramState *state = C.getState();
78
79  if (CE->getNumArgs() < 2) {
80    // The frontend should issue a warning for this case, so this is a sanity
81    // check.
82    return;
83  }
84
85  // Now check if oflags has O_CREAT set.
86  const Expr *oflagsEx = CE->getArg(1);
87  const SVal V = state->getSVal(oflagsEx);
88  if (!isa<NonLoc>(V)) {
89    // The case where 'V' can be a location can only be due to a bad header,
90    // so in this case bail out.
91    return;
92  }
93  NonLoc oflags = cast<NonLoc>(V);
94  NonLoc ocreateFlag =
95    cast<NonLoc>(C.getSValBuilder().makeIntVal(Val_O_CREAT.getValue(),
96                                                oflagsEx->getType()));
97  SVal maskedFlagsUC = C.getSValBuilder().evalBinOpNN(state, BO_And,
98                                                      oflags, ocreateFlag,
99                                                      oflagsEx->getType());
100  if (maskedFlagsUC.isUnknownOrUndef())
101    return;
102  DefinedSVal maskedFlags = cast<DefinedSVal>(maskedFlagsUC);
103
104  // Check if maskedFlags is non-zero.
105  const ProgramState *trueState, *falseState;
106  llvm::tie(trueState, falseState) = state->assume(maskedFlags);
107
108  // Only emit an error if the value of 'maskedFlags' is properly
109  // constrained;
110  if (!(trueState && !falseState))
111    return;
112
113  if (CE->getNumArgs() < 3) {
114    ExplodedNode *N = C.generateSink(trueState);
115    if (!N)
116      return;
117
118    LazyInitialize(BT_open, "Improper use of 'open'");
119
120    BugReport *report =
121      new BugReport(*BT_open,
122                            "Call to 'open' requires a third argument when "
123                            "the 'O_CREAT' flag is set", N);
124    report->addRange(oflagsEx->getSourceRange());
125    C.EmitReport(report);
126  }
127}
128
129//===----------------------------------------------------------------------===//
130// pthread_once
131//===----------------------------------------------------------------------===//
132
133void UnixAPIChecker::CheckPthreadOnce(CheckerContext &C,
134                                      const CallExpr *CE) const {
135
136  // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker.
137  // They can possibly be refactored.
138
139  if (CE->getNumArgs() < 1)
140    return;
141
142  // Check if the first argument is stack allocated.  If so, issue a warning
143  // because that's likely to be bad news.
144  const ProgramState *state = C.getState();
145  const MemRegion *R = state->getSVal(CE->getArg(0)).getAsRegion();
146  if (!R || !isa<StackSpaceRegion>(R->getMemorySpace()))
147    return;
148
149  ExplodedNode *N = C.generateSink(state);
150  if (!N)
151    return;
152
153  llvm::SmallString<256> S;
154  llvm::raw_svector_ostream os(S);
155  os << "Call to 'pthread_once' uses";
156  if (const VarRegion *VR = dyn_cast<VarRegion>(R))
157    os << " the local variable '" << VR->getDecl()->getName() << '\'';
158  else
159    os << " stack allocated memory";
160  os << " for the \"control\" value.  Using such transient memory for "
161  "the control value is potentially dangerous.";
162  if (isa<VarRegion>(R) && isa<StackLocalsSpaceRegion>(R->getMemorySpace()))
163    os << "  Perhaps you intended to declare the variable as 'static'?";
164
165  LazyInitialize(BT_pthreadOnce, "Improper use of 'pthread_once'");
166
167  BugReport *report = new BugReport(*BT_pthreadOnce, os.str(), N);
168  report->addRange(CE->getArg(0)->getSourceRange());
169  C.EmitReport(report);
170}
171
172//===----------------------------------------------------------------------===//
173// "malloc" with allocation size 0
174//===----------------------------------------------------------------------===//
175
176// FIXME: Eventually this should be rolled into the MallocChecker, but this
177// check is more basic and is valuable for widespread use.
178void UnixAPIChecker::CheckMallocZero(CheckerContext &C,
179                                     const CallExpr *CE) const {
180
181  // Sanity check that malloc takes one argument.
182  if (CE->getNumArgs() != 1)
183    return;
184
185  // Check if the allocation size is 0.
186  const ProgramState *state = C.getState();
187  SVal argVal = state->getSVal(CE->getArg(0));
188
189  if (argVal.isUnknownOrUndef())
190    return;
191
192  const ProgramState *trueState, *falseState;
193  llvm::tie(trueState, falseState) = state->assume(cast<DefinedSVal>(argVal));
194
195  // Is the value perfectly constrained to zero?
196  if (falseState && !trueState) {
197    ExplodedNode *N = C.generateSink(falseState);
198    if (!N)
199      return;
200
201    // FIXME: Add reference to CERT advisory, and/or C99 standard in bug
202    // output.
203
204    LazyInitialize(BT_mallocZero, "Undefined allocation of 0 bytes");
205
206    BugReport *report =
207      new BugReport(*BT_mallocZero, "Call to 'malloc' has an allocation"
208                                            " size of 0 bytes", N);
209    report->addRange(CE->getArg(0)->getSourceRange());
210    report->addVisitor(bugreporter::getTrackNullOrUndefValueVisitor(N,
211                                                                CE->getArg(0)));
212    C.EmitReport(report);
213    return;
214  }
215  // Assume the the value is non-zero going forward.
216  assert(trueState);
217  if (trueState != state) {
218    C.generateNode(trueState);
219  }
220}
221
222//===----------------------------------------------------------------------===//
223// Central dispatch function.
224//===----------------------------------------------------------------------===//
225
226void UnixAPIChecker::checkPreStmt(const CallExpr *CE, CheckerContext &C) const {
227  // Get the callee.  All the functions we care about are C functions
228  // with simple identifiers.
229  const ProgramState *state = C.getState();
230  const Expr *Callee = CE->getCallee();
231  const FunctionDecl *Fn = state->getSVal(Callee).getAsFunctionDecl();
232
233  if (!Fn)
234    return;
235
236  const IdentifierInfo *FI = Fn->getIdentifier();
237  if (!FI)
238    return;
239
240  SubChecker SC =
241    llvm::StringSwitch<SubChecker>(FI->getName())
242      .Case("open", &UnixAPIChecker::CheckOpen)
243      .Case("pthread_once", &UnixAPIChecker::CheckPthreadOnce)
244      .Case("malloc", &UnixAPIChecker::CheckMallocZero)
245      .Default(NULL);
246
247  if (SC)
248    (this->*SC)(C, CE);
249}
250
251//===----------------------------------------------------------------------===//
252// Registration.
253//===----------------------------------------------------------------------===//
254
255void ento::registerUnixAPIChecker(CheckerManager &mgr) {
256  mgr.registerChecker<UnixAPIChecker>();
257}
258