1 //== ReturnPointerRangeChecker.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 ReturnPointerRangeChecker, which is a path-sensitive check
10 // which looks for an out-of-bound pointer being returned to callers.
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 ReturnPointerRangeChecker :
27 public Checker< check::PreStmt<ReturnStmt> > {
28 mutable std::unique_ptr<BuiltinBug> BT;
29
30 public:
31 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
32 };
33 }
34
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const35 void ReturnPointerRangeChecker::checkPreStmt(const ReturnStmt *RS,
36 CheckerContext &C) const {
37 ProgramStateRef state = C.getState();
38
39 const Expr *RetE = RS->getRetValue();
40 if (!RetE)
41 return;
42
43 SVal V = C.getSVal(RetE);
44 const MemRegion *R = V.getAsRegion();
45
46 const ElementRegion *ER = dyn_cast_or_null<ElementRegion>(R);
47 if (!ER)
48 return;
49
50 DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
51 // Zero index is always in bound, this also passes ElementRegions created for
52 // pointer casts.
53 if (Idx.isZeroConstant())
54 return;
55
56 // FIXME: All of this out-of-bounds checking should eventually be refactored
57 // into a common place.
58 DefinedOrUnknownSVal ElementCount = getDynamicElementCount(
59 state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());
60
61 // We assume that the location after the last element in the array is used as
62 // end() iterator. Reporting on these would return too many false positives.
63 if (Idx == ElementCount)
64 return;
65
66 ProgramStateRef StInBound = state->assumeInBound(Idx, ElementCount, true);
67 ProgramStateRef StOutBound = state->assumeInBound(Idx, ElementCount, false);
68 if (StOutBound && !StInBound) {
69 ExplodedNode *N = C.generateErrorNode(StOutBound);
70
71 if (!N)
72 return;
73
74 // FIXME: This bug correspond to CWE-466. Eventually we should have bug
75 // types explicitly reference such exploit categories (when applicable).
76 if (!BT)
77 BT.reset(new BuiltinBug(
78 this, "Buffer overflow",
79 "Returned pointer value points outside the original object "
80 "(potential buffer overflow)"));
81
82 // FIXME: It would be nice to eventually make this diagnostic more clear,
83 // e.g., by referencing the original declaration or by saying *why* this
84 // reference is outside the range.
85
86 // Generate a report for this bug.
87 auto report =
88 std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N);
89
90 report->addRange(RetE->getSourceRange());
91 C.emitReport(std::move(report));
92 }
93 }
94
registerReturnPointerRangeChecker(CheckerManager & mgr)95 void ento::registerReturnPointerRangeChecker(CheckerManager &mgr) {
96 mgr.registerChecker<ReturnPointerRangeChecker>();
97 }
98
shouldRegisterReturnPointerRangeChecker(const CheckerManager & mgr)99 bool ento::shouldRegisterReturnPointerRangeChecker(const CheckerManager &mgr) {
100 return true;
101 }
102