Protection with capabilities

Less common in normal OS kernels.

• Though there are some good examples.

Example: open file descriptors.

• Applications’ processes indirectly manipulate (open) files through file descriptors kept by the OS kernel.

  • File descriptors are referenced using integer indexes (aka file descriptors for simplicity…).

  • The OS kernel has full control over the contents of open file descriptors.

• Access to open file descriptors can only be granted to other processes through the OS kernel.

  • Not really a usual operation, but possible!

• Changes in the protection of files do not impact existing open file descriptors.

  • The access rights are evaluated and memorized when the file is open.