MemoryUnsafeCastChecker.cpp

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//=======- MemoryUnsafeCastChecker.cpp -------------------------*- C++ -*-==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines MemoryUnsafeCast checker, which checks for casts from a
// base type to a derived type.
//===----------------------------------------------------------------------===//
 
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
 
using namespace clang;
using namespace ento;
using namespace ast_matchers;
 
namespace {
static constexpr const char *const BaseNode = "BaseNode";
static constexpr const char *const DerivedNode = "DerivedNode";
static constexpr const char *const FromCastNode = "FromCast";
static constexpr const char *const ToCastNode = "ToCast";
static constexpr const char *const WarnRecordDecl = "WarnRecordDecl";
 
class MemoryUnsafeCastChecker : public Checker<check::ASTCodeBody> {
  BugType BT{this, "Unsafe cast", "WebKit coding guidelines"};
 
public:
  void checkASTCodeBody(const Decl *D, AnalysisManager &Mgr,
                        BugReporter &BR) const;
};
} // end namespace
 
static void emitDiagnostics(const BoundNodes &Nodes, BugReporter &BR,
                            AnalysisDeclContext *ADC,
                            const MemoryUnsafeCastChecker *Checker,
                            const BugType &BT) {
  const auto *CE = Nodes.getNodeAs<CastExpr>(WarnRecordDecl);
  const NamedDecl *Base = Nodes.getNodeAs<NamedDecl>(BaseNode);
  const NamedDecl *Derived = Nodes.getNodeAs<NamedDecl>(DerivedNode);
  assert(CE && Base && Derived);
 
  std::string Diagnostics;
  llvm::raw_string_ostream OS(Diagnostics);
  OS << "Unsafe cast from base type '" << Base->getNameAsString()
     << "' to derived type '" << Derived->getNameAsString() << "'";
  PathDiagnosticLocation BSLoc(CE->getSourceRange().getBegin(),
                               BR.getSourceManager());
  auto Report = std::make_unique<BasicBugReport>(BT, OS.str(), BSLoc);
  Report->addRange(CE->getSourceRange());
  BR.emitReport(std::move(Report));
}
 
static void emitDiagnosticsUnrelated(const BoundNodes &Nodes, BugReporter &BR,
                                     AnalysisDeclContext *ADC,
                                     const MemoryUnsafeCastChecker *Checker,
                                     const BugType &BT) {
  const auto *CE = Nodes.getNodeAs<CastExpr>(WarnRecordDecl);
  const NamedDecl *FromCast = Nodes.getNodeAs<NamedDecl>(FromCastNode);
  const NamedDecl *ToCast = Nodes.getNodeAs<NamedDecl>(ToCastNode);
  assert(CE && FromCast && ToCast);
 
  std::string Diagnostics;
  llvm::raw_string_ostream OS(Diagnostics);
  OS << "Unsafe cast from type '" << FromCast->getNameAsString()
     << "' to an unrelated type '" << ToCast->getNameAsString() << "'";
  PathDiagnosticLocation BSLoc(CE->getSourceRange().getBegin(),
                               BR.getSourceManager());
  auto Report = std::make_unique<BasicBugReport>(BT, OS.str(), BSLoc);
  Report->addRange(CE->getSourceRange());
  BR.emitReport(std::move(Report));
}
 
namespace clang {
namespace ast_matchers {
AST_MATCHER_P(StringLiteral, mentionsBoundType, std::string, BindingID) {
  return Builder->removeBindings([this, &Node](const BoundNodesMap &Nodes) {
    const auto &BN = Nodes.getNode(this->BindingID);
    if (const auto *ND = BN.get<NamedDecl>()) {
      return ND->getName() != Node.getString();
    }
    return true;
  });
}
} // end namespace ast_matchers
} // end namespace clang
 
static decltype(auto) hasTypePointingTo(DeclarationMatcher DeclM) {
  return hasType(pointerType(pointee(hasDeclaration(DeclM))));
}
 
void MemoryUnsafeCastChecker::checkASTCodeBody(const Decl *D,
                                               AnalysisManager &AM,
                                               BugReporter &BR) const {
 
  AnalysisDeclContext *ADC = AM.getAnalysisDeclContext(D);
 
  // Match downcasts from base type to derived type and warn
  auto MatchExprPtr = allOf(
      hasSourceExpression(hasTypePointingTo(cxxRecordDecl().bind(BaseNode))),
      hasTypePointingTo(cxxRecordDecl(isDerivedFrom(equalsBoundNode(BaseNode)))
                            .bind(DerivedNode)),
      unless(anyOf(hasSourceExpression(cxxThisExpr()),
                   hasTypePointingTo(templateTypeParmDecl()))));
  auto MatchExprPtrObjC = allOf(
      hasSourceExpression(ignoringImpCasts(hasType(objcObjectPointerType(
          pointee(hasDeclaration(objcInterfaceDecl().bind(BaseNode))))))),
      ignoringImpCasts(hasType(objcObjectPointerType(pointee(hasDeclaration(
          objcInterfaceDecl(isDerivedFrom(equalsBoundNode(BaseNode)))
              .bind(DerivedNode)))))));
  auto MatchExprRefTypeDef =
      allOf(hasSourceExpression(hasType(hasUnqualifiedDesugaredType(recordType(
                hasDeclaration(decl(cxxRecordDecl().bind(BaseNode))))))),
            hasType(hasUnqualifiedDesugaredType(recordType(hasDeclaration(
                decl(cxxRecordDecl(isDerivedFrom(equalsBoundNode(BaseNode)))
                         .bind(DerivedNode)))))),
            unless(anyOf(hasSourceExpression(hasDescendant(cxxThisExpr())),
                         hasType(templateTypeParmDecl()))));
 
  auto ExplicitCast = explicitCastExpr(anyOf(MatchExprPtr, MatchExprRefTypeDef,
                                             MatchExprPtrObjC))
                          .bind(WarnRecordDecl);
  auto Cast = stmt(ExplicitCast);
 
  auto Matches =
      match(stmt(forEachDescendant(Cast)), *D->getBody(), AM.getASTContext());
  for (BoundNodes Match : Matches)
    emitDiagnostics(Match, BR, ADC, this, BT);
 
  // Match casts between unrelated types and warn
  auto MatchExprPtrUnrelatedTypes = allOf(
      hasSourceExpression(
          hasTypePointingTo(cxxRecordDecl().bind(FromCastNode))),
      hasTypePointingTo(cxxRecordDecl().bind(ToCastNode)),
      unless(anyOf(hasTypePointingTo(cxxRecordDecl(
                       isSameOrDerivedFrom(equalsBoundNode(FromCastNode)))),
                   hasSourceExpression(hasTypePointingTo(cxxRecordDecl(
                       isSameOrDerivedFrom(equalsBoundNode(ToCastNode))))))));
  auto MatchExprPtrObjCUnrelatedTypes = allOf(
      hasSourceExpression(ignoringImpCasts(hasType(objcObjectPointerType(
          pointee(hasDeclaration(objcInterfaceDecl().bind(FromCastNode))))))),
      ignoringImpCasts(hasType(objcObjectPointerType(
          pointee(hasDeclaration(objcInterfaceDecl().bind(ToCastNode)))))),
      unless(anyOf(
          ignoringImpCasts(hasType(
              objcObjectPointerType(pointee(hasDeclaration(objcInterfaceDecl(
                  isSameOrDerivedFrom(equalsBoundNode(FromCastNode)))))))),
          hasSourceExpression(ignoringImpCasts(hasType(
              objcObjectPointerType(pointee(hasDeclaration(objcInterfaceDecl(
                  isSameOrDerivedFrom(equalsBoundNode(ToCastNode))))))))))));
  auto MatchExprRefTypeDefUnrelated = allOf(
      hasSourceExpression(hasType(hasUnqualifiedDesugaredType(recordType(
          hasDeclaration(decl(cxxRecordDecl().bind(FromCastNode))))))),
      hasType(hasUnqualifiedDesugaredType(
          recordType(hasDeclaration(decl(cxxRecordDecl().bind(ToCastNode)))))),
      unless(anyOf(
          hasType(hasUnqualifiedDesugaredType(
              recordType(hasDeclaration(decl(cxxRecordDecl(
                  isSameOrDerivedFrom(equalsBoundNode(FromCastNode)))))))),
          hasSourceExpression(hasType(hasUnqualifiedDesugaredType(
              recordType(hasDeclaration(decl(cxxRecordDecl(
                  isSameOrDerivedFrom(equalsBoundNode(ToCastNode))))))))))));
 
  auto ExplicitCastUnrelated =
      explicitCastExpr(anyOf(MatchExprPtrUnrelatedTypes,
                             MatchExprPtrObjCUnrelatedTypes,
                             MatchExprRefTypeDefUnrelated))
          .bind(WarnRecordDecl);
  auto CastUnrelated = stmt(ExplicitCastUnrelated);
  auto MatchesUnrelatedTypes = match(stmt(forEachDescendant(CastUnrelated)),
                                     *D->getBody(), AM.getASTContext());
  for (BoundNodes Match : MatchesUnrelatedTypes)
    emitDiagnosticsUnrelated(Match, BR, ADC, this, BT);
}
 
void ento::registerMemoryUnsafeCastChecker(CheckerManager &Mgr) {
  Mgr.registerChecker<MemoryUnsafeCastChecker>();
}
 
bool ento::shouldRegisterMemoryUnsafeCastChecker(const CheckerManager &mgr) {
  return true;
}