ReturnPointerRangeChecker.cpp revision 6f42b62b6194f53bcbc349f5d17388e1936535d7 
1//== ReturnPointerRangeChecker.cpp ------------------------------*- 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 file defines ReturnPointerRangeChecker, which is a path-sensitive check
11// which looks for an out-of-bound pointer being returned to callers.
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/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
21
22using namespace clang;
23using namespace ento;
24
25namespace {
26class ReturnPointerRangeChecker :
27    public Checker< check::PreStmt<ReturnStmt> > {
28  mutable OwningPtr<BuiltinBug> BT;
29public:
30    void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
31};
32}
33
34void ReturnPointerRangeChecker::checkPreStmt(const ReturnStmt *RS,
35                                             CheckerContext &C) const {
36  ProgramStateRef state = C.getState();
37
38  const Expr *RetE = RS->getRetValue();
39  if (!RetE)
40    return;
41
42  SVal V = state->getSVal(RetE, C.getLocationContext());
43  const MemRegion *R = V.getAsRegion();
44
45  const ElementRegion *ER = dyn_cast_or_null<ElementRegion>(R);
46  if (!ER)
47    return;
48
49  DefinedOrUnknownSVal Idx = cast<DefinedOrUnknownSVal>(ER->getIndex());
50  // Zero index is always in bound, this also passes ElementRegions created for
51  // pointer casts.
52  if (Idx.isZeroConstant())
53    return;
54  // FIXME: All of this out-of-bounds checking should eventually be refactored
55  // into a common place.
56
57  DefinedOrUnknownSVal NumElements
58    = C.getStoreManager().getSizeInElements(state, ER->getSuperRegion(),
59                                           ER->getValueType());
60
61  ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true);
62  ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false);
63  if (StOutBound && !StInBound) {
64    ExplodedNode *N = C.generateSink(StOutBound);
65
66    if (!N)
67      return;
68
69    // FIXME: This bug correspond to CWE-466.  Eventually we should have bug
70    // types explicitly reference such exploit categories (when applicable).
71    if (!BT)
72      BT.reset(new BuiltinBug("Return of pointer value outside of expected range",
73           "Returned pointer value points outside the original object "
74           "(potential buffer overflow)"));
75
76    // FIXME: It would be nice to eventually make this diagnostic more clear,
77    // e.g., by referencing the original declaration or by saying *why* this
78    // reference is outside the range.
79
80    // Generate a report for this bug.
81    BugReport *report =
82      new BugReport(*BT, BT->getDescription(), N);
83
84    report->addRange(RetE->getSourceRange());
85    C.EmitReport(report);
86  }
87}
88
89void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) {
90  mgr.registerChecker<ReturnPointerRangeChecker>();
91}
92