[9front] notes on user none

[Anthony Martin <ality@pbrane.org>]

I remembered investigating the restrictions on user none
in the past so I went and dug out my notes. They're only
applicable to fossil and cwfs, though, so someone else
will have to go through the hjfs code to compare.

The notes are attached below.

Cheers,
  Anthony

# from /sys/doc/9.ms
Finally, a special user called none has no password and is always
allowed to connect; anyone may claim to be none. None has restricted
permissions; for example, it is not allowed to examine dump files and
can read only world-readable files.

# from /sys/doc/auth.ms
Factotum is the only process that needs to create capabilities, so all
the network servers can run as untrusted users (e.g., Plan 9's none or
Unix's nobody), which greatly reduces the harm done if a server is
buggy and is compromised.


# kernel
- documented
	- anyone can become none with none(8)
- undocumented
	- eve can change the owner of proc(3) files to none
	- none cannot use proc(3) to view or modify the state of other processes
	- none cannot create shr(3) files on 9front

# cwfs(4) and fossil(4)
- documented
	- none cannot authenticate a connection
		- auth(5) with uname "none" returns Rerror
	- none can be chaperoned on authenticated connections
		- attach(5) with afid NOFID sets uname to "none"
	- none has minimal access permissions (i.e. "world" or "other")
	- users in the "noworld" group are denied world access permissions
- undocumented
	- none cannot be a group leader
		- wstat(5) is limited

# fossil(4)
- documented
	- none cannot attach to an unauthenticated connection
		- unless the -N flag is given to listen or srv
	- users not in the "write" group cannot modify the file system
		- unless the group doesn't exist
- undocumented
	- none cannot modify file status information
		- wstat(5) returns Rerror

# cwfs(4)
- documented
	- none *can* attach to an unauthenticated connection
		- unless the nonone flag is set on 9front (undocumented)
- undocumented
	- none cannot attach to the dump file system
		- attach(5) returns Rerror