lib/fuchsia/pkg/avb/libavb/avb_descriptor.c

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "avb_descriptor.h"
#include "avb_util.h"
#include "avb_vbmeta_image.h"

bool avb_descriptor_validate_and_byteswap(const AvbDescriptor* src,
                                          AvbDescriptor* dest) {
  dest->tag = avb_be64toh(src->tag);
  dest->num_bytes_following = avb_be64toh(src->num_bytes_following);

  if ((dest->num_bytes_following & 0x07) != 0) {
    avb_error("Descriptor size is not divisible by 8.\n");
    return false;
  }
  return true;
}

bool avb_descriptor_foreach(const uint8_t* image_data,
                            size_t image_size,
                            AvbDescriptorForeachFunc foreach_func,
                            void* user_data) {
  const AvbVBMetaImageHeader* header = NULL;
  bool ret = false;
  const uint8_t* image_end;
  const uint8_t* desc_start;
  const uint8_t* desc_end;
  const uint8_t* p;
  uint64_t desc_offset = 0;
  uint64_t desc_size = 0;

  if (image_data == NULL) {
    avb_error("image_data is NULL\n.");
    goto out;
  }

  if (foreach_func == NULL) {
    avb_error("foreach_func is NULL\n.");
    goto out;
  }

  /* The data is supposed to have been cryptographically verified at this point,
   * This check is just adding defense in depth.
   */
  if (image_size < sizeof(AvbVBMetaImageHeader)) {
    avb_error("Length is smaller than header.\n");
    goto out;
  }

  /* Ensure magic is correct. */
  if (avb_memcmp(image_data, AVB_MAGIC, AVB_MAGIC_LEN) != 0) {
    avb_error("Magic is incorrect.\n");
    goto out;
  }

  /* Careful, not byteswapped - also ensure it's aligned properly. */
  avb_assert_aligned(image_data);
  header = (const AvbVBMetaImageHeader*)image_data;
  image_end = image_data + image_size;

  /* Since the data is supposed to have been cryptographically verified at this
   * point, being overflow-safe is just for defense.
   * The following lines are overflow-safe version of:
   * desc_offset = sizeof(AvbVBMetaImageHeader) +
   *               avb_be64toh(header->authentication_data_block_size)) +
   *               avb_be64toh(header->descriptors_offset)
   */
  if (!avb_safe_add(&desc_offset,
                    sizeof(AvbVBMetaImageHeader),
                    avb_be64toh(header->authentication_data_block_size))) {
    avb_error("Invalid authentication data block size.\n");
    goto out;
  }
  if (!avb_safe_add_to(&desc_offset, avb_be64toh(header->descriptors_offset))) {
    avb_error("Invalid descriptors offset.\n");
    goto out;
  }

  if (desc_offset > (uint64_t)(image_end - image_data)) {
    avb_error("Descriptors not inside passed-in data.\n");
    goto out;
  }

  desc_start = image_data + desc_offset;

  desc_size = avb_be64toh(header->descriptors_size);
  if (desc_size > (uint64_t)(image_end - desc_start)) {
    avb_error("Descriptors not inside passed-in data.\n");
    goto out;
  }

  desc_end = desc_start + desc_size;

  for (p = desc_start; p < desc_end;) {
    if (p + sizeof(AvbDescriptor) > desc_end) {
      avb_error("Invalid descriptor length.\n");
      goto out;
    }
    const AvbDescriptor* dh = (const AvbDescriptor*)p;
    uint64_t nb_following;
    uint64_t nb_total = 0;
    avb_assert_aligned(dh);
    nb_following = avb_be64toh(dh->num_bytes_following);

    if (!avb_safe_add(&nb_total, sizeof(AvbDescriptor), nb_following)) {
      avb_error("Invalid descriptor length.\n");
      goto out;
    }

    if ((nb_total & 7) != 0) {
      avb_error("Invalid descriptor length.\n");
      goto out;
    }

    if (nb_total > (uint64_t)(desc_end - p)) {
      avb_error("Invalid data in descriptors array.\n");
      goto out;
    }

    if (foreach_func(dh, user_data) == 0) {
      goto out;
    }

    p += nb_total;
  }

  ret = true;

out:
  return ret;
}

static bool count_descriptors(const AvbDescriptor* descriptor,
                              void* user_data) {
  size_t* num_descriptors = user_data;
  *num_descriptors += 1;
  return true;
}

typedef struct {
  size_t descriptor_number;
  const AvbDescriptor** descriptors;
} SetDescriptorData;

static bool set_descriptors(const AvbDescriptor* descriptor, void* user_data) {
  SetDescriptorData* data = user_data;
  data->descriptors[data->descriptor_number++] = descriptor;
  return true;
}

const AvbDescriptor** avb_descriptor_get_all(const uint8_t* image_data,
                                             size_t image_size,
                                             size_t* out_num_descriptors) {
  size_t num_descriptors = 0;
  SetDescriptorData data;

  avb_descriptor_foreach(
      image_data, image_size, count_descriptors, &num_descriptors);

  data.descriptor_number = 0;
  data.descriptors =
      avb_calloc(sizeof(const AvbDescriptor*) * (num_descriptors + 1));
  if (data.descriptors == NULL) {
    return NULL;
  }
  avb_descriptor_foreach(image_data, image_size, set_descriptors, &data);
  avb_assert(data.descriptor_number == num_descriptors);

  if (out_num_descriptors != NULL) {
    *out_num_descriptors = num_descriptors;
  }

  return data.descriptors;
}