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plarae-fs - Process Level Access Restricted And Encrypted File System

An attempt to make a virtual file system that can control file permissions on a process level.

Usage

To run:

python3 -m plaraefs mount <fname> <mountpoint>

Where <fname> is the file containing the filesystem data (does not need to exist) and <mountpoint> is the directory to mount it to (needs to exist).

Warning!

This code is in active development and will break / change API without blinking. Seriously, don't use this!

Requirements

Optional:

Filesystem structure

Constants

All numbers in bytes

  • PHYSICAL_BLOCK_SIZE
    • The size of the encrypted blocks written by the cryptographic block system
    • Default: 4096 (4 KiB)
  • IV_SIZE
    • The size of the initialisation vector for AES
    • Default: 16
  • TAG_SIZE
    • The size of the AEAD tag used for authentication
    • Default: 16
  • LOGICAL_BLOCK_SIZE
    • The block size exposed by the cryptographic block system
    • Value: PHYSICAL_BLOCK_SIZE - IV_SIZE - TAG_SIZE
    • Default: 4064
  • BLOCK_ID_SIZE
    • The address size for addressing blocks
    • Default: 8 (64 bit address)
  • FILENAME_SIZE
    • The length of filenames (path components)
    • Default: 256
  • FILESIZE_SIZE
    • The largest possible file
    • Default: 8 (max file size of 2**64)
  • XATTR_INLINE_SIZE
    • The length of the embedded xattr field
    • Default: 256

Superblock

  • Positioned every LOGICAL_BLOCK_SIZE * 8 blocks
  • Contains bitmap of free blocks

File header block

  • Starts with mode byte
  • Followed by FILESIZE_SIZE 64-bit int representing the file size.
  • Followed by BLOCK_ID_SIZE block id for the next file continuation block, 0 if there isn't one
  • Followed by 32 BLOCK_ID_SIZE block ids indicating the next blocks
  • Followed by BLOCK_ID_SIZE block id for xattr additional space
  • Followed by XATTR_INLINE_SIZE xattr storage
  • Followed by data

File header continuation block

  • Starts BLOCK_ID_SIZE block id for the next file continuation block, 0 if there isn't one
  • Followed by BLOCK_ID_SIZE block id for the previous file continuation block
  • Followed by 32 BLOCK_ID_SIZE block ids indicating the next blocks
  • Followed by data

Normal file

  • Mode byte is 0
  • File data is contained in data section

Directory

  • Mode byte is 1
  • Data is subfiles encoded in the following way:
    • FILENAME_SIZE subfile name
    • Followed by BLOCK_ID_SIZE block id to the file header block

Maximums

  • Maximum file system size is 276 bytes (4 ZiB)
  • Maximum file size is 264 bytes (16 EiB)