Landlock Posix Message Queue Control

Review Thread | 🐞 Bug

Review notes:

• API for POSIX message queues: mq_open(), mq_close(), mq_unlink() etc.
• Under the hood,
  • IPC namespace holds a reference to the mqueuefs
  • Operates on files in that file system as a registration mechanism
• mqueuefs can be mounted on /dev/mqueue using:

  mount -t mqueue none /dev/mqueue
  

Maybe surprisingly, LANDLOCK_ACCESS_FS_READ_FILE and LANDLOCK_ACCESS_FS_WRITE_FILE already restrict the opening of mqueuefs files, and that extends to opens happening through mq_open(2)!