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
22using namespace clang;
23using namespace ento;
24
25namespace {
26class CastToStructVisitor : public RecursiveASTVisitor<CastToStructVisitor> {
27  BugReporter &BR;
28  const CheckerBase *Checker;
29  AnalysisDeclContext *AC;
30
31public:
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
39bool 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
108namespace {
109class CastToStructChecker : public Checker<check::ASTCodeBody> {
110public:
111  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
119void ento::registerCastToStructChecker(CheckerManager &mgr) {
120  mgr.registerChecker<CastToStructChecker>();
121}
122
123bool ento::shouldRegisterCastToStructChecker(const CheckerManager &mgr) {
124  return true;
125}
126