1 //== ArrayBoundChecker.cpp ------------------------------*- C++ -*--==//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines ArrayBoundChecker, which is a path-sensitive check
10 // which looks for an out-of-bound array element access.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.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/PathSensitive/DynamicExtent.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
21 
22 using namespace clang;
23 using namespace ento;
24 
25 namespace {
26 class ArrayBoundChecker :
27     public Checker<check::Location> {
28   mutable std::unique_ptr<BuiltinBug> BT;
29 
30 public:
31   void checkLocation(SVal l, bool isLoad, const Stmt* S,
32                      CheckerContext &C) const;
33 };
34 }
35 
36 void ArrayBoundChecker::checkLocation(SVal l, bool isLoad, const Stmt* LoadS,
37                                       CheckerContext &C) const {
38   // Check for out of bound array element access.
39   const MemRegion *R = l.getAsRegion();
40   if (!R)
41     return;
42 
43   const ElementRegion *ER = dyn_cast<ElementRegion>(R);
44   if (!ER)
45     return;
46 
47   // Get the index of the accessed element.
48   DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
49 
50   // Zero index is always in bound, this also passes ElementRegions created for
51   // pointer casts.
52   if (Idx.isZeroConstant())
53     return;
54 
55   ProgramStateRef state = C.getState();
56 
57   // Get the size of the array.
58   DefinedOrUnknownSVal ElementCount = getDynamicElementCount(
59       state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());
60 
61   ProgramStateRef StInBound = state->assumeInBound(Idx, ElementCount, true);
62   ProgramStateRef StOutBound = state->assumeInBound(Idx, ElementCount, false);
63   if (StOutBound && !StInBound) {
64     ExplodedNode *N = C.generateErrorNode(StOutBound);
65     if (!N)
66       return;
67 
68     if (!BT)
69       BT.reset(new BuiltinBug(
70           this, "Out-of-bound array access",
71           "Access out-of-bound array element (buffer overflow)"));
72 
73     // FIXME: It would be nice to eventually make this diagnostic more clear,
74     // e.g., by referencing the original declaration or by saying *why* this
75     // reference is outside the range.
76 
77     // Generate a report for this bug.
78     auto report =
79         std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N);
80 
81     report->addRange(LoadS->getSourceRange());
82     C.emitReport(std::move(report));
83     return;
84   }
85 
86   // Array bound check succeeded.  From this point forward the array bound
87   // should always succeed.
88   C.addTransition(StInBound);
89 }
90 
91 void ento::registerArrayBoundChecker(CheckerManager &mgr) {
92   mgr.registerChecker<ArrayBoundChecker>();
93 }
94 
95 bool ento::shouldRegisterArrayBoundChecker(const CheckerManager &mgr) {
96   return true;
97 }
98