From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net V2] vhost-vsock: fix use after free Date: Thu, 27 Sep 2018 19:50:24 -0400 Message-ID: <20180927194734-mutt-send-email-mst@kernel.org> References: <20180927122204.4188-1-jasowang@redhat.com> <20180927123539-mutt-send-email-mst@kernel.org> <588ed28b-7e4b-9dc8-92ce-d75692836c9e@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: stefanha@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, sergei.shtylyov@cogentembedded.com To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <588ed28b-7e4b-9dc8-92ce-d75692836c9e@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Sep 28, 2018 at 07:37:37AM +0800, Jason Wang wrote: > > > On 2018年09月28日 01:04, Michael S. Tsirkin wrote: > > On Thu, Sep 27, 2018 at 08:22:04PM +0800, Jason Wang wrote: > > > The access of vsock is not protected by vhost_vsock_lock. This may > > > lead to use after free since vhost_vsock_dev_release() may free the > > > pointer at the same time. > > > > > > Fix this by holding the lock during the access. > > > > > > Reported-by:syzbot+e3e074963495f92a89ed@syzkaller.appspotmail.com > > > Fixes: 16320f363ae1 ("vhost-vsock: add pkt cancel capability") > > > Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko") > > > Cc: Stefan Hajnoczi > > > Signed-off-by: Jason Wang > > Wow is that really the best we can do? > > For net/stable, probably yes. > > > A global lock on a data path > > operation? > > It's already there, &vhost_vsock_lock? were is it takes on data path? > and the patch only increase the critical section. > > > Granted use after free is nasty but Stefan said he sees > > a way to fix it using a per socket refcount. He's on vacation > > until Oct 4 though ... > > > > Stefan has acked the pacth, so I think it's ok? We can do optimization for > -next on top. > > Thanks Well on high SMP serializing can drop performance as much as x100 so I'm not sure it's appropriate - seems to fix a bug but can introduce a regression. Let's see how does a proper fix look first? -- MST