linux-kernel - Re: RFC: fsyscall

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Message-ID: <20150910140415.GB28113@mail.hallyn.com>
Date:	Thu, 10 Sep 2015 09:04:15 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	David Drysdale <drysdale@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andy Lutomirski <luto@...capital.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: RFC: fsyscall

On Thu, Sep 10, 2015 at 09:03:08AM -0500, Serge E. Hallyn wrote:
> On Thu, Sep 10, 2015 at 09:01:20AM -0500, Serge E. Hallyn wrote:
> > On Thu, Sep 10, 2015 at 02:51:28PM +0100, David Drysdale wrote:
> > > On Thu, Sep 10, 2015 at 2:43 PM, Serge E. Hallyn <serge@...lyn.com> wrote:
> > > > On Tue, Sep 08, 2015 at 07:25:17PM -0500, Eric W. Biederman wrote:
> > > >> Andy Lutomirski <luto@...capital.net> writes:
> > > >>
> > > >> > On Tue, Sep 8, 2015 at 4:07 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> > > >>
> > > >> >> Perhaps I had missed it but I don't recall capsicum being able to wrap
> > > >> >> things like reboot(2).
> > > >> >>
> > > >> >
> > > >> > Ah, so you want to be able to grant BPF-defined capabilities :)
> > > >>
> > > >> Pretty much.
> > > >>
> > > >> Where I am focusing is turning Posix capabilities into real
> > > >> capabilities.  I would not mind if the functionality was a bit more
> > > >> general.  Say to be able to handle things like security labels, or
> > > >> anywhere else you might reasonably be asked can you do X?
> > > >>
> > > >> But I would be happy if we just managed to wrap the Posix capabilities
> > > >> and turned them into real capablilities.
> > > >
> > > > If there were a clever way to exec an open fd, then you could do this
> > > 
> > > execveat(fd, "", argv, envp, AT_EMPTY_PATH) ?
> > 
> > ???  I looked for it but I don't have a manpage for it.  I see it at
> > man7.org though.  Thanks :)
> 
> But this isn't quite what I was suggesting.  I was suggesting a call which
> would exec the fd, not exec a file inside the dirfd.

Oh, which it does:

   If pathname is an empty string and the AT_EMPTY_PATH flag is
       specified, then the file descriptor dirfd specifies the file to be
       executed (i.e., dirfd refers to an executable file, rather than a
       directory).

well that's spiffy
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