Date: Fri, 27 Nov 2020 08:41:39 -0600 From: Kyle Evans <kevans@freebsd.org> To: "Bjoern A. Zeeb" <bz@freebsd.org> Cc: freebsd-jail <freebsd-jail@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org>, trustedbsd-discuss@freebsd.org Subject: Re: RFC: Jail privsets Message-ID: <CACNAnaGdn4o84UmKfA=m-fWvaUSHj-1zTVsBe9cdZZy0JMzEKg@mail.gmail.com> In-Reply-To: <06F654BB-B087-4AE5-8599-E5837A85A850@FreeBSD.org> References: <CACNAnaEKoBppjG8HH0KgYQv0EHPUcHmB3teyw1PQrjG3xsbXYQ@mail.gmail.com> <06F654BB-B087-4AE5-8599-E5837A85A850@FreeBSD.org>
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On Fri, Nov 27, 2020 at 6:15 AM Bjoern A. Zeeb <bz@freebsd.org> wrote: > > On 27 Nov 2020, at 5:04, Kyle Evans wrote: > > > (Cross-posting to -arch and -jail for maximum reach) > > and trustedbsd now as that is where priv(9) came from [ > http://www.trustedbsd.org/privileges.html ] > > > A couple of times recently, I've had a need or desire to increase or > > decrease privileges available to jails I create to some extent. You > > can write a MAC policy for this, but at some point the downsides of > > MAC policies for this became clear: it's either non-trivial to allow > > the kind of flexibility you may need in configuring some of these > > jails, and you have to rebuild the module otherwise. > > > > I've got a generally functional patch at [1] that is an approach I'd > > like to request comments on for refining jail privileges. It creates a > > privset that can be assigned on a per-jail basis, and a creator with > > PRIV_JAIL_SETPRIVS can specify any privset mask that's a subset of the > > parent prison. > > > > If no privset was specified at creation time, then we use the default > > logic that was previously in prison_priv_check(). prison_priv_check() > > has been replaced with a much simpler check of the prison's privset > > for the given privilege. > > > > As I was writing this, I identified the first problem with it: it > > doesn't currently respond to ALLOW_* updates and grant the appropriate > > privileges after initialization time -- this is a pretty easy fix, and > > I will do so if anyone else finds this useful. > > > > The other caveat is that I have no idea if there's a useful way to > > expose this to jail(8) users, but they're not really the primary > > target for this -- the primary target is system application developers > > that want more fine control over what a jail they're creating can do. > > > > This is an excellent foot-gun, but with great power comes great > > responsibility. > > While I like the idea I am not sure I like the way it is done. > > I think it was a long-time goal of Robert (which just never happened to > day) to make priv(9) configurable from user space. > > I am just not sure if hanging it off jails is the right answer. > The jail-set is certainly the most extensive in the system, but the priv > checks are everywhere and hanging them off, say a thread or credential, > would allow people to do a lot more (also non-foot-shooting) than just > modifying jails. > > That said, jails pretty much tie into the entire td/cred concept already > so we could happily use them as a jumping platform for experimenting > before extending it to the entire system if we are clear that this might > not be the final stable way of doing things? > Hi, So, FWIW, I had mapped this out a little further in my head but hadn't quite decided on the best approach so I had stuck to jails for the time being because that's the scenario that crops up the most for me thus far. Here's the line of reasoning I went through up to this point, for full disclosure: cred-based seems like a good approach, but the caveat is that they're a little more difficult to target in a meaningful way to the admin, AFAICT. I really like cpuset(1) and the accompanying interfaces, as there's a lot of flexibility to be had there. It uses relatable concepts that have obvious semantics: - You can restrict a jail, it cascades down - You can restrict a process, it cascades down - You can restrict a thread So I started there at the first level, because it doesn't actually preclude the later levels. As you step down the tree, I think you simply step away from the need to have prison_priv_check() at all and just naturally push it all down into priv_check() because the fact that they're in a jail has either already been accounted for or is now completely irrelevant. Thanks, Kyle Evans
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