cpdf_linearized_header.cpp

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// Copyright 2016 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
#include "core/fpdfapi/parser/cpdf_linearized_header.h"
 
#include <algorithm>
#include <limits>
#include <utility>
 
#include "core/fpdfapi/parser/cpdf_array.h"
#include "core/fpdfapi/parser/cpdf_dictionary.h"
#include "core/fpdfapi/parser/cpdf_number.h"
#include "core/fpdfapi/parser/cpdf_parser.h"
#include "core/fpdfapi/parser/cpdf_syntax_parser.h"
#include "core/fxcrt/fx_safe_types.h"
#include "third_party/base/check.h"
#include "third_party/base/memory/ptr_util.h"
 
namespace {
 
constexpr FX_FILESIZE kLinearizedHeaderOffset = 9;
constexpr size_t kMaxInt = static_cast<size_t>(std::numeric_limits<int>::max());
 
template <class T>
bool IsValidNumericDictionaryValue(const CPDF_Dictionary* pDict,
                                   const ByteString& key,
                                   T min_value,
                                   bool must_exist = true) {
  if (!pDict->KeyExist(key))
    return !must_exist;
  RetainPtr<const CPDF_Number> pNum = pDict->GetNumberFor(key);
  if (!pNum || !pNum->IsInteger())
    return false;
  const int raw_value = pNum->GetInteger();
  if (!pdfium::base::IsValueInRangeForNumericType<T>(raw_value))
    return false;
  return static_cast<T>(raw_value) >= min_value;
}
 
bool IsLinearizedHeaderValid(const CPDF_LinearizedHeader* header,
                             FX_FILESIZE document_size) {
  DCHECK(header);
  return header->GetFileSize() == document_size &&
         header->GetFirstPageNo() < kMaxInt &&
         header->GetFirstPageNo() < header->GetPageCount() &&
         header->GetMainXRefTableFirstEntryOffset() < document_size &&
         header->GetFirstPageEndOffset() < document_size &&
         header->GetFirstPageObjNum() < CPDF_Parser::kMaxObjectNumber &&
         header->GetLastXRefOffset() < document_size &&
         header->GetHintStart() < document_size;
}
 
}  // namespace
 
// static
std::unique_ptr<CPDF_LinearizedHeader> CPDF_LinearizedHeader::Parse(
    CPDF_SyntaxParser* parser) {
  parser->SetPos(kLinearizedHeaderOffset);
 
  const auto pDict = ToDictionary(
      parser->GetIndirectObject(nullptr, CPDF_SyntaxParser::ParseType::kLoose));
 
  if (!pDict || !pDict->KeyExist("Linearized") ||
      !IsValidNumericDictionaryValue<FX_FILESIZE>(pDict.Get(), "L", 1) ||
      !IsValidNumericDictionaryValue<uint32_t>(pDict.Get(), "P", 0, false) ||
      !IsValidNumericDictionaryValue<FX_FILESIZE>(pDict.Get(), "T", 1) ||
      !IsValidNumericDictionaryValue<uint32_t>(pDict.Get(), "N", 1) ||
      !IsValidNumericDictionaryValue<FX_FILESIZE>(pDict.Get(), "E", 1) ||
      !IsValidNumericDictionaryValue<uint32_t>(pDict.Get(), "O", 1)) {
    return nullptr;
  }
  // Move parser to the start of the xref table for the documents first page.
  // (skpping endobj keyword)
  if (parser->GetNextWord().word != "endobj")
    return nullptr;
 
  auto result = pdfium::WrapUnique(
      new CPDF_LinearizedHeader(pDict.Get(), parser->GetPos()));
 
  if (!IsLinearizedHeaderValid(result.get(), parser->GetDocumentSize()))
    return nullptr;
 
  return result;
}
 
CPDF_LinearizedHeader::CPDF_LinearizedHeader(const CPDF_Dictionary* pDict,
                                             FX_FILESIZE szLastXRefOffset)
    : m_szFileSize(pDict->GetIntegerFor("L")),
      m_dwFirstPageNo(pDict->GetIntegerFor("P")),
      m_szMainXRefTableFirstEntryOffset(pDict->GetIntegerFor("T")),
      m_PageCount(pDict->GetIntegerFor("N")),
      m_szFirstPageEndOffset(pDict->GetIntegerFor("E")),
      m_FirstPageObjNum(pDict->GetIntegerFor("O")),
      m_szLastXRefOffset(szLastXRefOffset) {
  RetainPtr<const CPDF_Array> pHintStreamRange = pDict->GetArrayFor("H");
  const size_t nHintStreamSize =
      pHintStreamRange ? pHintStreamRange->size() : 0;
  if (nHintStreamSize == 2 || nHintStreamSize == 4) {
    m_szHintStart = std::max(pHintStreamRange->GetIntegerAt(0), 0);
    const FX_SAFE_UINT32 safe_hint_length = pHintStreamRange->GetIntegerAt(1);
    if (safe_hint_length.IsValid())
      m_HintLength = safe_hint_length.ValueOrDie();
  }
}
 
CPDF_LinearizedHeader::~CPDF_LinearizedHeader() = default;
 
bool CPDF_LinearizedHeader::HasHintTable() const {
  return GetPageCount() > 1 && GetHintStart() > 0 && GetHintLength() > 0;
}