clang/lib/StaticAnalyzer/Checkers/CastToStructChecker.cpp

   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:
  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
  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:
 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
 119 void ento::registerCastToStructChecker(CheckerManager &mgr) {
 120   mgr.registerChecker<CastToStructChecker>();
 121 }
 122
 123 bool ento::shouldRegisterCastToStructChecker(const CheckerManager &mgr) {
 124   return true;
 125 }