[9fans] Plan9 permissions

[G. David Butler gdb@dbSystems.com]

From: rsc@plan9.bell-labs.com
>	I think the paragraph should read:
>
>	"When the owner attempts to do something to a file, the owner
>	permissions are consulted only, and if they grant the requested
>	permission, the operation is allowed.  For someone who is not the
>	owner, but is a member of the files's group, only the group
>	permissions are consulted.  The other permissions are only used
>	if the requestor is not the owner or a member of the file's group."
>
>but then it wouldn't be true.

You could have assumed the following:

int
iaccess(File *f, Dentry *d, int m)
{
	/*
	 * various forms of superuser
	 */
	if(writeallow)
		return 0;
	if(wstatallow && d->mode & DDIR)
		return 0;
	if(duallow && duallow == f->uid &&
	  d->mode & DDIR && (m == DREAD || m == DEXEC))
		return 0;
	/*
	 * owner is next
	 */
	if(f->uid == d->uid) {
		if(m << 6 & d->mode)
			return 0;
		else
			return 1;
	}
	/*
	 * group membership is hard
	 */
	if(ingroup(f->uid, d->gid)) {
		if(m << 3 & d->mode)
			return 0;
		else
			return 1;
	}
	/*
	 * other is easiest
	 */
	if(m & d->mode)
		return 0;
	else
		return 1;
}

Take for example the incoming directory for anonymous ftp,
/usr/none/incoming.

My way it can be:

d--wxrwxr-x M X none none

Your way it has to be:

d--wx-wx-wx M X none none (you have to change perms to see contents)
	or
d--wxrwx-wx M X none sys (or something not none)

>it is silly to honor permissions that are not
>monotonically nonincreasing (octal digitwise)
>from owner to everyone.

Huh?

>if you are the owner and the permissions are
>something like 466, then you can just change them
>with chmod.  if you are in the group and the 
>permissions are something like 446 or 646, then
>you can just become none (echo -n none >/dev/user)
>and then you have permission again.

So, you are the owner.

>look at /sys/src/fs/port/sub.c:/^iaccess
>on the cd.

Things Change.