Re: [PATCH net V2] vhost-vsock: fix use after free

[Jason Wang]

On 2018å09æ28æ 07:50, Michael S. Tsirkin wrote:
> On Fri, Sep 28, 2018 at 07:37:37AM +0800, Jason Wang wrote:
> > On 2018å09æ28æ 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > Fixes: 16320f363ae1 ("vhost-vsock: add pkt cancel capability")
> > > > Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
> > > > Cc: Stefan Hajnoczi<stefanha@xxxxxxxxxx>
> > > > Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx>
> > > 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?

Ok, but the current code use list which means a global lock is needed 
anyway here.

> > 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?

It looks to me hlist + RCU is better. But I'm not sure it's suitable for 
-net/-stable.

Thanks