From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753004AbeC0N7C (ORCPT ); Tue, 27 Mar 2018 09:59:02 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:52298 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752590AbeC0N7A (ORCPT ); Tue, 27 Mar 2018 09:59:00 -0400 Date: Tue, 27 Mar 2018 16:58:59 +0300 From: "Michael S. Tsirkin" To: Jason Wang Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] vhost: correctly remove wait queue during poll failure Message-ID: <20180327165330-mutt-send-email-mst@kernel.org> References: <1522122442-30317-1-git-send-email-jasowang@redhat.com> <20180327092811.ikvssyxgb74nucb4@dhcp-10-175-199-170.vpn.oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 27, 2018 at 05:43:14PM +0800, Jason Wang wrote: > > > On 2018年03月27日 17:28, Darren Kenny wrote: > > Hi Jason, > > > > On Tue, Mar 27, 2018 at 11:47:22AM +0800, Jason Wang wrote: > > > We tried to remove vq poll from wait queue, but do not check whether > > > or not it was in a list before. This will lead double free. Fixing > > > this by checking poll->wqh to make sure it was in a list. > > > > This text seems at odds with the code below, instead of checking > > poll-whq, you are removing that check... > > > > Maybe the text needs rewording? > > Yes, I admit it's bad, thanks for pointing out. > > How about: > > "Fixing this by switching to use vhost_poll_stop() which zeros poll->wqh > after removing poll from waitqueue to make sure it won't be freed twice." > > Thanks Let's be a bit more specific about the problem maybe? when vhost's attempt to start polling a descriptor fails, we remove the poll->wqh entry from wait queue but do not clear it, so the following cleanup (e.g. on release) will attempt to remove it again. To fix, switch to vhost_poll_stop() which zeros poll->wqh after removing poll from waitqueue to make sure it won't be freed twice." the patch itself is fine though: Acked-by: Michael S. Tsirkin > > > > Thanks, > > > > Darren. > > > > > > > > Reported-by: syzbot+c0272972b01b872e604a@syzkaller.appspotmail.com > > > Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting > > > backend") > > > Signed-off-by: Jason Wang > > > --- > > > drivers/vhost/vhost.c | 3 +-- > > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index 1b3e8d2d..5d5a9d9 100644 > > > --- a/drivers/vhost/vhost.c > > > +++ b/drivers/vhost/vhost.c > > > @@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll, > > > struct file *file) > > >     if (mask) > > >         vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask)); > > >     if (mask & EPOLLERR) { > > > -        if (poll->wqh) > > > -            remove_wait_queue(poll->wqh, &poll->wait); > > > +        vhost_poll_stop(poll); > > >         ret = -EINVAL; > > >     } > > > > > > -- > > > 2.7.4 > > >