Patched code sample

import io

def process_pdf_data_fixed(data_stream):
    """
    A simplified function demonstrating the fix for a Denial of Service
    vulnerability caused by uncontrolled parenthesis nesting in a PDF parser.

    The fix, represented here, introduces a depth limit to halt parsing
    of a malicious file before the process hangs. This is based on the
    patch for the real-world vulnerability CVE-2022-45198, which matches
    the user's description.
    """
    # The vulnerability was a lack of limits on parenthesis nesting.
    # The fix is to introduce and enforce a maximum depth.
    MAX_NESTING_DEPTH = 100
    nesting = 0

    while True:
        char = data_stream.read(1)
        if not char:
            break

        if char == b"(":
            # FIX: Check the nesting depth before proceeding.
            if nesting >= MAX_NESTING_DEPTH:
                # If the depth is exceeded, raise an error instead of
                # continuing, which prevents a Denial of Service.
                raise ValueError(
                    f"PDF parsing error: Exceeded max parenthesis nesting depth of {MAX_NESTING_DEPTH}"
                )
            nesting += 1
        elif char == b")":
            if nesting <= 0:
                raise ValueError("PDF parsing error: Mismatched closing parenthesis")
            nesting -= 1

    # In a real scenario, further checks would happen here.
    # The key is that the state is no longer vulnerable due to the check above.
    return "Parsed successfully."