1 //=== CastToStructChecker.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 files defines CastToStructChecker, a builtin checker that checks for
10 // cast from non-struct pointer to struct pointer and widening struct data cast.
11 // This check corresponds to CWE-588.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
16 #include "clang/AST/RecursiveASTVisitor.h"
17 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
18 #include "clang/StaticAnalyzer/Core/Checker.h"
19 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
21
22 using namespace clang;
23 using namespace ento;
24
25 namespace {
26 class CastToStructVisitor : public RecursiveASTVisitor<CastToStructVisitor> {
27 BugReporter &BR;
28 const CheckerBase *Checker;
29 AnalysisDeclContext *AC;
30
31 public:
CastToStructVisitor(BugReporter & B,const CheckerBase * Checker,AnalysisDeclContext * A)32 explicit CastToStructVisitor(BugReporter &B, const CheckerBase *Checker,
33 AnalysisDeclContext *A)
34 : BR(B), Checker(Checker), AC(A) {}
35 bool VisitCastExpr(const CastExpr *CE);
36 };
37 }
38
VisitCastExpr(const CastExpr * CE)39 bool CastToStructVisitor::VisitCastExpr(const CastExpr *CE) {
40 const Expr *E = CE->getSubExpr();
41 ASTContext &Ctx = AC->getASTContext();
42 QualType OrigTy = Ctx.getCanonicalType(E->getType());
43 QualType ToTy = Ctx.getCanonicalType(CE->getType());
44
45 const PointerType *OrigPTy = dyn_cast<PointerType>(OrigTy.getTypePtr());
46 const PointerType *ToPTy = dyn_cast<PointerType>(ToTy.getTypePtr());
47
48 if (!ToPTy || !OrigPTy)
49 return true;
50
51 QualType OrigPointeeTy = OrigPTy->getPointeeType();
52 QualType ToPointeeTy = ToPTy->getPointeeType();
53
54 if (!ToPointeeTy->isStructureOrClassType())
55 return true;
56
57 // We allow cast from void*.
58 if (OrigPointeeTy->isVoidType())
59 return true;
60
61 // Now the cast-to-type is struct pointer, the original type is not void*.
62 if (!OrigPointeeTy->isRecordType()) {
63 SourceRange Sr[1] = {CE->getSourceRange()};
64 PathDiagnosticLocation Loc(CE, BR.getSourceManager(), AC);
65 BR.EmitBasicReport(
66 AC->getDecl(), Checker, "Cast from non-struct type to struct type",
67 categories::LogicError, "Casting a non-structure type to a structure "
68 "type and accessing a field can lead to memory "
69 "access errors or data corruption.",
70 Loc, Sr);
71 } else {
72 // Don't warn when size of data is unknown.
73 const auto *U = dyn_cast<UnaryOperator>(E);
74 if (!U || U->getOpcode() != UO_AddrOf)
75 return true;
76
77 // Don't warn for references
78 const ValueDecl *VD = nullptr;
79 if (const auto *SE = dyn_cast<DeclRefExpr>(U->getSubExpr()))
80 VD = SE->getDecl();
81 else if (const auto *SE = dyn_cast<MemberExpr>(U->getSubExpr()))
82 VD = SE->getMemberDecl();
83 if (!VD || VD->getType()->isReferenceType())
84 return true;
85
86 if (ToPointeeTy->isIncompleteType() ||
87 OrigPointeeTy->isIncompleteType())
88 return true;
89
90 // Warn when there is widening cast.
91 unsigned ToWidth = Ctx.getTypeInfo(ToPointeeTy).Width;
92 unsigned OrigWidth = Ctx.getTypeInfo(OrigPointeeTy).Width;
93 if (ToWidth <= OrigWidth)
94 return true;
95
96 PathDiagnosticLocation Loc(CE, BR.getSourceManager(), AC);
97 BR.EmitBasicReport(AC->getDecl(), Checker, "Widening cast to struct type",
98 categories::LogicError,
99 "Casting data to a larger structure type and accessing "
100 "a field can lead to memory access errors or data "
101 "corruption.",
102 Loc, CE->getSourceRange());
103 }
104
105 return true;
106 }
107
108 namespace {
109 class CastToStructChecker : public Checker<check::ASTCodeBody> {
110 public:
checkASTCodeBody(const Decl * D,AnalysisManager & Mgr,BugReporter & BR) const111 void checkASTCodeBody(const Decl *D, AnalysisManager &Mgr,
112 BugReporter &BR) const {
113 CastToStructVisitor Visitor(BR, this, Mgr.getAnalysisDeclContext(D));
114 Visitor.TraverseDecl(const_cast<Decl *>(D));
115 }
116 };
117 } // end anonymous namespace
118
registerCastToStructChecker(CheckerManager & mgr)119 void ento::registerCastToStructChecker(CheckerManager &mgr) {
120 mgr.registerChecker<CastToStructChecker>();
121 }
122
shouldRegisterCastToStructChecker(const CheckerManager & mgr)123 bool ento::shouldRegisterCastToStructChecker(const CheckerManager &mgr) {
124 return true;
125 }
126