Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753600AbcKPIVn (ORCPT ); Wed, 16 Nov 2016 03:21:43 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:39946 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752169AbcKPIVl (ORCPT ); Wed, 16 Nov 2016 03:21:41 -0500 Date: Wed, 16 Nov 2016 09:21:51 +0100 From: Greg KH To: Kees Cook Cc: Peter Zijlstra , Will Deacon , "Reshetova, Elena" , Arnd Bergmann , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , David Windsor , LKML , Alexei Starovoitov , Daniel Borkmann Subject: Re: [RFC][PATCH 2/7] kref: Add kref_read() Message-ID: <20161116082151.GA24017@kroah.com> References: <20161114173946.501528675@infradead.org> <20161114174446.486581399@infradead.org> <20161115073322.GC28248@kroah.com> <20161115080314.GD3142@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3063 Lines: 82 On Tue, Nov 15, 2016 at 12:53:35PM -0800, Kees Cook wrote: > On Tue, Nov 15, 2016 at 12:03 AM, Peter Zijlstra wrote: > > On Tue, Nov 15, 2016 at 08:33:22AM +0100, Greg KH wrote: > >> On Mon, Nov 14, 2016 at 06:39:48PM +0100, Peter Zijlstra wrote: > > > >> > --- a/drivers/block/drbd/drbd_req.c > >> > +++ b/drivers/block/drbd/drbd_req.c > >> > @@ -520,7 +520,7 @@ static void mod_rq_state(struct drbd_req > >> > /* Completion does it's own kref_put. If we are going to > >> > * kref_sub below, we need req to be still around then. */ > >> > int at_least = k_put + !!c_put; > >> > - int refcount = atomic_read(&req->kref.refcount); > >> > + int refcount = kref_read(&req->kref); > >> > if (refcount < at_least) > >> > drbd_err(device, > >> > "mod_rq_state: Logic BUG: %x -> %x: refcount = %d, should be >= %d\n", > >> > >> As proof of "things you should never do", here is one such example. > >> > >> ugh. > >> > >> > >> > --- a/drivers/block/virtio_blk.c > >> > +++ b/drivers/block/virtio_blk.c > >> > @@ -767,7 +767,7 @@ static void virtblk_remove(struct virtio > >> > /* Stop all the virtqueues. */ > >> > vdev->config->reset(vdev); > >> > > >> > - refc = atomic_read(&disk_to_dev(vblk->disk)->kobj.kref.refcount); > >> > + refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref); > >> > put_disk(vblk->disk); > >> > vdev->config->del_vqs(vdev); > >> > kfree(vblk->vqs); > >> > >> And this too, ugh, that's a huge abuse and is probably totally wrong... > >> > >> thanks again for digging through this crap. I wonder if we need to name > >> the kref reference variable "do_not_touch_this_ever" or some such thing > >> to catch all of the people who try to be "too smart". > > > > There's unimaginable bong hits involved in this stuff, in the end I > > resorted to brute force and scripts to convert all this. > > What should we do about things like this (bpf_prog_put() and callbacks > from kernel/bpf/syscall.c): > > > static void bpf_prog_uncharge_memlock(struct bpf_prog *prog) > { > struct user_struct *user = prog->aux->user; > > atomic_long_sub(prog->pages, &user->locked_vm); Oh that's scary. Let's just make one reference count rely on another one and not check things... > free_uid(user); > } > > static void __bpf_prog_put_rcu(struct rcu_head *rcu) > { > struct bpf_prog_aux *aux = container_of(rcu, struct bpf_prog_aux, rcu); > > free_used_maps(aux); > bpf_prog_uncharge_memlock(aux->prog); > bpf_prog_free(aux->prog); > } > > void bpf_prog_put(struct bpf_prog *prog) > { > if (atomic_dec_and_test(&prog->aux->refcnt)) > call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu); > } > > > Not only do we want to protect prog->aux->refcnt, but I think we want > to protect user->locked_vm too ... I don't think it's sane for > user->locked_vm to be a stats_t ? I don't think this is sane code... greg k-h