Re: [9fans] Drawterm /mnt/term permissions issue

[erik quanstrom <quanstro@quanstro.net>]

On Fri Jun  5 01:21:25 EDT 2009, eekee57@fastmail.fm wrote:
> On Thu, 4 Jun 2009 17:23:08 -0700
> Russ Cox <rsc@swtch.com> wrote:
>
> > On Thu, Jun 4, 2009 at 4:58 PM, Ethan Grammatikidis <eekee57@fastmail.fm> wrote:
> > > I run a plan 9 cpu server in Qemu and use drawterm to connect from the Linux host.
> > > I thought the /mnt/term mechanism would be very convenient for exchanging files
> > > between host & guest, but the guest sees all user/group names as
> > > unknown/unknown, preventing writing.
> >
> > That's surprising.  Drawterm isn't going around enforcing
> > permission bits: if it can write, it writes.  What it shows
> > you in ls is what it gets from stat, but it doesn't rely on
> > that to make decisions about what you can open.  It just
> > tries to open it.
>
> Oh now I get it: drawterm isn't enforcing permissions ,,,

correct,

> but the plan 9 kernel is, on seeing a dir with user/group = unknown/unknown and perms bits = 755 it won't allow creation within that dir. At least, I assume that's what's going on.

incorrect.  the linux kernel is checking the file's permissions against the
euid/egid of the drawterm process.

unknown/unknown are just filler that drawterm provides.  perhaps it
should say "(this space reserved for a user name if we had one)", but
that would be rather long and would break the general convention that
usernames in plan 9 do not have spaces or punctuation.

(bonus points for the first explot by a fs injecting shell script goo
into user/group name.  ☺)

- erik