Patched code sample

import os
import subprocess

# A list of trusted locations for executables.
TRUSTED_BASE_PATHS = ("/usr/bin/", "/usr/local/bin/", os.path.expanduser("~/.local/bin/"))

def run_linter(file_to_lint):
    """
    Runs a linter on a given file, allowing path override via an
    environment variable for user convenience.
    """
    linter_executable = "pylint"  # Default tool

    custom_linter_path = os.environ.get("PYTHON_LINTER_PATH")
    if custom_linter_path:
        # FIX: The path is validated against an allow-list of trusted locations.
        resolved_path = os.path.realpath(custom_linter_path)
        if any(resolved_path.startswith(p) for p in TRUSTED_BASE_PATHS):
            linter_executable = custom_linter_path

    try:
        # Only a linter from a trusted path will be executed.
        subprocess.run(
            [linter_executable, file_to_lint],
            check=True,
            capture_output=True
        )
        return True
    except (subprocess.CalledProcessError, FileNotFoundError):
        return False