/*

 * HEIF codec.

 * Copyright (c) 2018 Dirk Farin <dirk.farin@gmail.com>

 *

 * This file is part of libheif.

 *

 * libheif is free software: you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as

 * published by the Free Software Foundation, either version 3 of

 * the License, or (at your option) any later version.

 *

 * libheif is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with libheif.  If not, see <http://www.gnu.org/licenses/>.

 */

#ifndef LIBHEIF_SECURITY_LIMITS_H

#define LIBHEIF_SECURITY_LIMITS_H

#include "libheif/heif.h"

#include <cinttypes>

#include <cstddef>

#include <set>

#include <atomic>

#include <memory>

#include "error.h"

extern heif_security_limits global_security_limits;

extern heif_security_limits disabled_security_limits;

// Maximum nesting level of boxes in input files.

// We put a limit on this to avoid unlimited stack usage by malicious input files.

static const int MAX_BOX_NESTING_LEVEL = 20;

static const int MAX_BOX_SIZE = 0x7FFFFFFF; // 2 GB

static const int64_t MAX_LARGE_BOX_SIZE = 0x0FFFFFFFFFFFFFFF;

static const int64_t MAX_FILE_POS = 0x007FFFFFFFFFFFFFLL; // maximum file position

static const int MAX_FRACTION_VALUE = 0x10000;

// Maximum number of 'iovl' overlay images that may be nested inside one another

// along a single decode path. Real files use at most one overlay per decode

// chain, so this is a structural sanity limit, not a common-case constraint.

static const uint32_t MAX_OVERLAY_NESTING_LEVEL = 3;

// Maximum number of input images that a single 'iovl' overlay may composite.

// This is a hardcoded stopgap until a configurable security-limit field can be

// added to heif_security_limits in the next major release (that is an API/ABI

// change and cannot go into a point release).

static const uint32_t MAX_OVERLAY_IMAGES = 5;

// Factor applied to max_items to bound the total number of sub-image decode

// operations triggered by a single top-level decode. Derived images (grid,

// iovl, iden) can reference the same base image through indirection, and the

// cycle-detection set is per-path (it forks at every branch), so a shared

// subtree can be re-decoded once per path that reaches it. Nested sharing makes

// the number of decode operations grow as branch^depth, which is bounded only

// by the recursion depth (<= number of items). Because a well-formed file

// decodes each of its (<= max_items) items a small number of times, capping the

// total at a modest multiple of max_items stops the exponential blow-up while

// leaving every realistic file untouched.  (GHSA-x8xm-cm2c-cfc8, variants V1/V2.)

static const uint32_t MAX_DERIVED_IMAGE_DECODE_FACTOR = 2;

// Traversal state threaded through the derived-image decode recursion for one

// top-level decode. It is copied by value at every hop, which gives the two

// members opposite (and intended) sharing semantics:

//

//   - processed_ids and overlay_nesting are plain values, so each recursion

//     branch gets its own copy. processed_ids is a per-path cycle guard;

//     overlay_nesting counts the overlays nested along the current path.

//

//   - decode_count is a shared_ptr to an atomic, so every copy (including the

//     copies handed to parallel tile-decode threads) shares one global counter

//     that bounds the total number of decode operations.

//

// A default-constructed DecodeTraversalState (max_decodes == 0) imposes no limit; the

// budget is seeded once at the top level in HeifContext::decode_image().

struct DecodeTraversalState

{

  std::set<heif_item_id> processed_ids;

  uint32_t overlay_nesting = 0;         // number of overlays on the path to here

  uint32_t max_overlay_nesting = 0;     // 0 == unlimited

  std::shared_ptr<std::atomic<uint32_t>> decode_count;

  uint32_t max_decodes = 0;             // 0 == unlimited

  // Count one sub-image decode against the shared budget.

  // Returns false when the budget has been exhausted.

  bool count_decode()

  {

    if (max_decodes == 0 || !decode_count) {

      return true;

    }

    return decode_count->fetch_add(1, std::memory_order_relaxed) < max_decodes;

  }

};

Error check_for_valid_image_size(const heif_security_limits* limits, uint32_t width, uint32_t height);

// Maximum coding-unit size (in pixels) that the given codec may pad a coded

// frame up to. Used as the margin for tighten_image_size_limit_for_ispe.

// Returns 0 for codecs without coding-unit padding (e.g. uncompressed).

uint32_t max_coding_unit_size_for_codec(heif_compression_format format);

// Return a copy of `base` with max_image_size_pixels lowered to a value

// just above the declared image size. This is used to bound how much memory

// a codec plugin may allocate for an image whose internal (codec-declared)

// dimensions exceed the file-declared (ispe) dimensions — without us having

// to parse the codec bitstream ourselves.

//

// `coding_unit_size` is the maximum coding-unit size of the target codec

// (e.g. 128 for AV1/VVC, 64 for HEVC, 16 for AVC). The allowed coded

// dimensions are (ispe + coding_unit_size) in each axis, since a codec may

// pad the coded frame up to a coding-unit boundary.

//

// The allowed size never drops below MIN_TIGHTENED_CODED_IMAGE_PIXELS: the

// HEVC/AVC conformance window may crop arbitrarily much, and hardware

// encoders use minimum surface sizes far above tiny image dimensions (issue

// #1856 has a conformant 2x2 HEIC coded as a 160x64 frame). The floor keeps

// the worst-case allocation for a lying bitstream small while accepting such

// padded coded frames; check_decoded_image_size() still validates the

// decoded output against 'ispe' afterwards.

static const uint64_t MIN_TIGHTENED_CODED_IMAGE_PIXELS = 65536;  // 256x256

heif_security_limits tighten_image_size_limit_for_ispe(const heif_security_limits* base,

                                                       uint32_t ispe_width,

                                                       uint32_t ispe_height,

                                                       uint32_t coding_unit_size);

class TotalMemoryTracker

{

public:

  explicit TotalMemoryTracker(const heif_security_limits* limits_context);

  ~TotalMemoryTracker();

  size_t get_max_total_memory_used() const;

  void operator=(const TotalMemoryTracker&) = delete;

  TotalMemoryTracker(const TotalMemoryTracker&) = delete;

private:

  const heif_security_limits* m_limits_context = nullptr;

};

class MemoryHandle

{

public:

  MemoryHandle() = default;

  ~MemoryHandle() { free(); }

  Error alloc(size_t memory_amount, const heif_security_limits* limits_context, const char* reason_description);

  // calloc-style overload: checks `count * element_size` for size_t overflow before allocating.

  // Use this when allocating an array whose total size is count*element_size, to avoid silent

  // truncation on 32-bit builds when count is near UINT32_MAX.

  Error alloc(size_t count, size_t element_size,

              const heif_security_limits* limits_context, const char* reason_description);

  void free();

  void free(size_t memory_amount);

  const heif_security_limits* get_security_limits() const { return m_limits_context; }

  MemoryHandle(const MemoryHandle&) = delete;

  MemoryHandle& operator=(const MemoryHandle&) = delete;

  MemoryHandle(MemoryHandle&& other) noexcept

      : m_limits_context(other.m_limits_context), m_memory_amount(other.m_memory_amount)

  {

    other.m_limits_context = nullptr;

    other.m_memory_amount = 0;

  }

  MemoryHandle& operator=(MemoryHandle&& other) noexcept

  {

    if (this != &other) {

      free();

      m_limits_context = other.m_limits_context;

      m_memory_amount = other.m_memory_amount;

      other.m_limits_context = nullptr;

      other.m_memory_amount = 0;

    }

    return *this;

  }

private:

  const heif_security_limits* m_limits_context = nullptr;

  size_t m_memory_amount = 0;

};

#endif  // LIBHEIF_SECURITY_LIMITS_H