system: You are an expert security code reviewer. You will be shown a source code file along with a multiple-choice question listing several function or class names from that file. Your task is to identify which one contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the single letter of the correct option, wrapped in \boxed{...}. Example: `\boxed{B}`. Output the boxed letter ONLY -- no explanation, no other text.

user: ```python
# Copyright (C) 2019 Intel Corporation
# SPDX-License-Identifier: BSD-3-Clause
"""
Contains utility functions for common operations, including:
- Checking file extensions
- Opening files for writing
- Checking paths
"""

from os.path import splitext
import os
import collections
from collections.abc import Iterable
import hashlib

import logging

import json
import jsonschema

_coverage_schema_id = (
    "https://raw.githubusercontent.com/intel/"
    "p3-analysis-library/p3/schema/coverage-0.1.0.schema"
)
_coverage_schema = {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "$id": _coverage_schema_id,
    "title": "Coverage",
    "description": "Lines of code used in each file of a code base.",
    "type": "array",
    "items": {
        "type": "object",
        "properties": {
            "file": {"type": "string"},
            "regions": {
                "type": "array",
                "items": {
                    "type": "array",
                    "prefixItems": [
                        {"type": "integer"},
                        {"type": "integer"},
                        {"type": "integer"},
                    ],
                    "items": False,
                },
            },
        },
        "required": ["file", "regions"],
    },
}

log = logging.getLogger("codebasin")


def compute_file_hash(fname):
    """Return sha512 for fname"""
    chunk_size = 4096
    hasher = hashlib.sha512()
    with safe_open_read_nofollow(fname, 'rb') as in_file:
        for chunk in iter(lambda: in_file.read(chunk_size), b""):
            hasher.update(chunk)
    return hasher.hexdigest()


def ensure_ext(fname, extensions):
    """Return true if the path passed in has specified extension"""
    if not isinstance(extensions, Iterable):
        extensions = [extensions]

    split = splitext(fname)
    return len(split) == 2 and split[1].lower() in extensions


def ensure_png(fname):
    """Return true if the path passed in specifies a png"""
    return ensure_ext(fname, ".png")


def ensure_source(fname):
    """Return true if the path passed in specifies a source file"""
    extensions = [".s", ".asm", ".c", ".cpp", ".cxx", ".c++", ".cc",
                  ".h", ".hpp", ".hxx", ".h++", ".hh",
                  ".inc", ".inl", ".tcc", ".icc", ".ipp"]
    return ensure_ext(fname, extensions)


def ensure_yaml(fname):
    """Return true if the path passed in specifies a YAML file"""
    return ensure_ext(fname, ".yaml")


def ensure_json(fname):
    """Return true if the path passed in specifies a JSON file"""
    return ensure_ext(fname, ".json")


def safe_open_write_binary(fname):
    """Open fname for (binary) writing. Truncate if not a symlink."""
    fpid = os.open(fname, os.O_WRONLY | os.O_CREAT | os.O_TRUNC | os.O_NOFOLLOW, 0o666)
    return os.fdopen(fpid, "wb")


def safe_open_read_nofollow(fname, *args, **kwargs):
    """Open fname for reading, but don't follow links."""
    fpid = os.open(fname, os.O_RDONLY | os.O_NOFOLLOW)
    return os.fdopen(fpid, *args, **kwargs)


def valid_path(path):
    """Return true if the path passed in is valid"""
    valid = True

    # Check for null byte character(s)
    if '\x00' in path:
        log.critical("Null byte character in file request.")
        valid = False

    # Check for carriage returns or line feed character(s)
    if ('\n' in path) or ('\r' in path):
        log.critical("Carriage return or line feed character in file request.")
        valid = False

    return valid


def validate_coverage_json(json_string: str) -> bool:
    """
    Validate coverage JSON string against schema.

    Parameters
    ----------
    json_string : String
        The JSON string to validate.

    Returns
    -------
    bool
        True if the JSON string is valid.

    Raises
    ------
    ValueError
        If the JSON string fails to validate.

    TypeError
        If the JSON string is not a string.
    """
    if not isinstance(json_string, str):
        raise TypeError("Coverage must be a JSON string.")

    instance = json.loads(json_string)

    try:
        jsonschema.validate(instance=instance, schema=_coverage_schema)
    except Exception:
        msg = "Coverage string failed schema validation"
        raise ValueError(msg)

    return True

```

Which of the following functions or classes contains a `CWE-732: Incorrect Permission Assignment for Critical Resource` vulnerability?

  A) validate_coverage_json
  B) safe_open_write_binary
  C) valid_path
  D) ensure_png
Answer: B