Allegro
49097ba09e
Add atomic_write.py with temp file + rename pattern to prevent Time-of-Check to Time-of-Use race conditions in file operations. CVSS: 7.4 (High) Refs: V-015 CWE-367: TOCTOU Race Condition
65 lines
2.0 KiB
Python
65 lines
2.0 KiB
Python
"""Atomic file write operations to prevent TOCTOU race conditions.
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SECURITY FIX (V-015): Implements atomic writes using temp files + rename
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to prevent Time-of-Check to Time-of-Use race conditions.
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CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition
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"""
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import os
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import tempfile
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from pathlib import Path
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from typing import Union
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def atomic_write(path: Union[str, Path], content: str, mode: str = "w") -> None:
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"""Atomically write content to file using temp file + rename.
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This prevents TOCTOU race conditions where the file could be
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modified between checking permissions and writing.
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Args:
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path: Target file path
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content: Content to write
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mode: Write mode ("w" for text, "wb" for bytes)
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"""
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path = Path(path)
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path.parent.mkdir(parents=True, exist_ok=True)
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# Write to temp file in same directory (same filesystem for atomic rename)
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fd, temp_path = tempfile.mkstemp(
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dir=path.parent,
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prefix=f".tmp_{path.name}.",
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suffix=".tmp"
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)
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try:
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if "b" in mode:
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os.write(fd, content if isinstance(content, bytes) else content.encode())
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else:
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os.write(fd, content.encode() if isinstance(content, str) else content)
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os.fsync(fd) # Ensure data is written to disk
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finally:
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os.close(fd)
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# Atomic rename - this is guaranteed to be atomic on POSIX
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os.replace(temp_path, path)
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def safe_read_write(path: Union[str, Path], content: str) -> dict:
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"""Safely read and write file with TOCTOU protection.
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Returns:
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dict with status and error message if any
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"""
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try:
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# SECURITY: Use atomic write to prevent race conditions
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atomic_write(path, content)
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return {"success": True, "error": None}
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except PermissionError as e:
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return {"success": False, "error": f"Permission denied: {e}"}
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except OSError as e:
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return {"success": False, "error": f"OS error: {e}"}
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except Exception as e:
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return {"success": False, "error": f"Unexpected error: {e}"}
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