From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Allison Subject: Re: Thoughts on credential switching Date: Thu, 27 Mar 2014 11:56:48 -0700 Message-ID: <20140327185648.GE2526@jeremy-laptop> References: <53341D8E.80105@redhat.com> <20140327060225.4f4caa5a@ipyr.poochiereds.net> <53342258.8000304@redhat.com> <20140327070126.41ac75ac@ipyr.poochiereds.net> <20140327182617.GC2526@jeremy-laptop> Reply-To: Jeremy Allison Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jeremy Allison , Jeff Layton , Florian Weimer , Jim Lieb , "Eric W. Biederman" , LSM List , "Serge E. Hallyn" , Kees Cook , Linux FS Devel , Theodore Ts'o , "linux-kernel@vger.kernel.org" , bfields@redhat.com To: Andy Lutomirski Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Mar 27, 2014 at 11:46:39AM -0700, Andy Lutomirski wrote: > On Thu, Mar 27, 2014 at 11:26 AM, Jeremy Allison wrote: > > > > Amen to that :-). > > > > However, after talking with Jeff and Jim at CollabSummit, > > I was 'encouraged' to make my opinions known on the list. > > > > To me, calling the creds handle a file descriptor just > > feels wrong. IT *isn't* an fd, you can't read/write/poll > > on it, and it's only done as a convenience to get the > > close-on-exec semantics and the fact that the creds are > > already hung off the fd's in kernel space. > > Windows calls these things "handles." Linux has "file descriptors," > and there's plenty of precedent for things that aren't files. Sure, but there's a set of expectations around fd's that these things don't satisfy - IO-ops. > > That way we can also make it clear this thing only has > > meaning to a thread group, and SHOULD NOT (and indeed > > preferably CAN NOT) be passed between processes. > > > > If you want those semantics, then stick a struct pid * in there for > the tgid of the cretor and make sure that current's tgid matches when > you try to use it. > > I think they'd be more useful without that check, though. I'm more worried about leakage and unintended consequences here. > BTW, what do you want to have happen on fork? I think they should keep working. Yeah, that's true. I want them to keep working across fork, but not across exec or any other method of fd-passing. Jeremy.