static int BROTLI_NOINLINE BrotliAllocateRingBuffer(BrotliState* s,
    BrotliBitReader* br) {
  /* We need the slack region for the following reasons:
      - doing up to two 16-byte copies for fast backward copying
      - inserting transformed dictionary word (5 prefix + 24 base + 8 suffix) */
  static const int kRingBufferWriteAheadSlack = 42;
  int is_last = s->is_last_metablock;
  s->ringbuffer_size = 1 << s->window_bits;

  if (s->is_uncompressed) {
    int next_block_header = BrotliPeekByte(br,
        (size_t)s->meta_block_remaining_len);
    if (next_block_header != -1) { /* Peek succeeded */
      if ((next_block_header & 3) == 3) { /* ISLAST and ISEMPTY */
        is_last = 1;
      }
    }
  }

  /* We need at least 2 bytes of ring buffer size to get the last two
     bytes for context from there */
  if (is_last) {
    while (s->ringbuffer_size >= s->meta_block_remaining_len * 2
        && s->ringbuffer_size > 32) {
      s->ringbuffer_size >>= 1;
    }
  }

  /* But make it fit the custom dictionary if there is one. */
  while (s->ringbuffer_size < s->custom_dict_size) {
    s->ringbuffer_size <<= 1;
  }

  s->ringbuffer_mask = s->ringbuffer_size - 1;
  s->ringbuffer = (uint8_t*)BROTLI_ALLOC(s, (size_t)(s->ringbuffer_size +
      kRingBufferWriteAheadSlack + kBrotliMaxDictionaryWordLength));
  if (s->ringbuffer == 0) {
    return 0;
  }
  s->ringbuffer_end = s->ringbuffer + s->ringbuffer_size;
  s->ringbuffer[s->ringbuffer_size - 2] = 0;
  s->ringbuffer[s->ringbuffer_size - 1] = 0;
  if (s->custom_dict) {
    memcpy(&s->ringbuffer[(-s->custom_dict_size) & s->ringbuffer_mask],
                          s->custom_dict, (size_t)s->custom_dict_size);
  }

  return 1;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.