Re: [PATCH net V4] virtio-net: fix the race between refill work and close

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jul 04, 2022 at 02:32:45PM +0800, Jason Wang wrote:
> On Mon, Jul 4, 2022 at 2:19 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Mon, Jul 04, 2022 at 12:19:48PM +0800, Jason Wang wrote:
> > > We try using cancel_delayed_work_sync() to prevent the work from
> > > enabling NAPI. This is insufficient since we don't disable the source
> > > of the refill work scheduling. This means an NAPI poll callback after
> > > cancel_delayed_work_sync() can schedule the refill work then can
> > > re-enable the NAPI that leads to use-after-free [1].
> > >
> > > Since the work can enable NAPI, we can't simply disable NAPI before
> > > calling cancel_delayed_work_sync(). So fix this by introducing a
> > > dedicated boolean to control whether or not the work could be
> > > scheduled from NAPI.
> > >
> > > [1]
> > > ==================================================================
> > > BUG: KASAN: use-after-free in refill_work+0x43/0xd4
> > > Read of size 2 at addr ffff88810562c92e by task kworker/2:1/42
> > >
> > > CPU: 2 PID: 42 Comm: kworker/2:1 Not tainted 5.19.0-rc1+ #480
> > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> > > Workqueue: events refill_work
> > > Call Trace:
> > >  <TASK>
> > >  dump_stack_lvl+0x34/0x44
> > >  print_report.cold+0xbb/0x6ac
> > >  ? _printk+0xad/0xde
> > >  ? refill_work+0x43/0xd4
> > >  kasan_report+0xa8/0x130
> > >  ? refill_work+0x43/0xd4
> > >  refill_work+0x43/0xd4
> > >  process_one_work+0x43d/0x780
> > >  worker_thread+0x2a0/0x6f0
> > >  ? process_one_work+0x780/0x780
> > >  kthread+0x167/0x1a0
> > >  ? kthread_exit+0x50/0x50
> > >  ret_from_fork+0x22/0x30
> > >  </TASK>
> > > ...
> > >
> > > Fixes: b2baed69e605c ("virtio_net: set/cancel work on ndo_open/ndo_stop")
> > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > ---
> > > Changes since V3:
> > > - rebase to -net
> > > Changes since V2:
> > > - use spin_unlock()/lock_bh() in open/stop to synchronize with bh
> > > Changes since V1:
> > > - Tweak the changelog
> > > ---
> > >  drivers/net/virtio_net.c | 35 +++++++++++++++++++++++++++++++++--
> > >  1 file changed, 33 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 356cf8dd4164..68430d7923ac 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -251,6 +251,12 @@ struct virtnet_info {
> > >       /* Does the affinity hint is set for virtqueues? */
> > >       bool affinity_hint_set;
> > >
> > > +     /* Is refill work enabled? */
> >
> > refilling enabled
> 
> I think it should be reill work, we try refill first, if fail we
> schedule the work:
> 
>                 if (!try_fill_recv(vi, rq, GFP_ATOMIC))
>                         schedule_delayed_work(&vi->refill, 0);
> 
> Thanks

maybe "delayed refill"? It's not "work" it's a work struct.
I'm trying to be consistent with:
        /* Work struct for refilling if we run low on memory. */
        struct delayed_work refill;


> >
> > > +     bool refill_work_enabled;
> >
> >
> > refill_work -> refill?
> >
> > > +
> > > +     /* The lock to synchronize the access to refill_work_enabled */
> >
> > .. and refill
> >
> > And maybe put these field near the refill field.
> >
> > > +     spinlock_t refill_lock;
> > > +
> > >       /* CPU hotplug instances for online & dead */
> > >       struct hlist_node node;
> > >       struct hlist_node node_dead;
> > > @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
> > >       return p;
> > >  }
> > >
> > > +static void enable_refill_work(struct virtnet_info *vi)
> > > +{
> > > +     spin_lock_bh(&vi->refill_lock);
> > > +     vi->refill_work_enabled = true;
> > > +     spin_unlock_bh(&vi->refill_lock);
> > > +}
> > > +
> > > +static void disable_refill_work(struct virtnet_info *vi)
> > > +{
> > > +     spin_lock_bh(&vi->refill_lock);
> > > +     vi->refill_work_enabled = false;
> > > +     spin_unlock_bh(&vi->refill_lock);
> > > +}
> > > +
> > >  static void virtqueue_napi_schedule(struct napi_struct *napi,
> > >                                   struct virtqueue *vq)
> > >  {
> > > @@ -1527,8 +1547,12 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
> > >       }
> > >
> > >       if (rq->vq->num_free > min((unsigned int)budget, virtqueue_get_vring_size(rq->vq)) / 2) {
> > > -             if (!try_fill_recv(vi, rq, GFP_ATOMIC))
> > > -                     schedule_delayed_work(&vi->refill, 0);
> > > +             if (!try_fill_recv(vi, rq, GFP_ATOMIC)) {
> > > +                     spin_lock(&vi->refill_lock);
> > > +                     if (vi->refill_work_enabled)
> > > +                             schedule_delayed_work(&vi->refill, 0);
> > > +                     spin_unlock(&vi->refill_lock);
> > > +             }
> > >       }
> > >
> > >       u64_stats_update_begin(&rq->stats.syncp);
> > > @@ -1651,6 +1675,8 @@ static int virtnet_open(struct net_device *dev)
> > >       struct virtnet_info *vi = netdev_priv(dev);
> > >       int i, err;
> > >
> > > +     enable_refill_work(vi);
> > > +
> > >       for (i = 0; i < vi->max_queue_pairs; i++) {
> > >               if (i < vi->curr_queue_pairs)
> > >                       /* Make sure we have some buffers: if oom use wq. */
> > > @@ -2033,6 +2059,8 @@ static int virtnet_close(struct net_device *dev)
> > >       struct virtnet_info *vi = netdev_priv(dev);
> > >       int i;
> > >
> > > +     /* Make sure NAPI doesn't schedule refill work */
> > > +     disable_refill_work(vi);
> > >       /* Make sure refill_work doesn't re-enable napi! */
> > >       cancel_delayed_work_sync(&vi->refill);
> > >
> > > @@ -2792,6 +2820,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
> > >
> > >       virtio_device_ready(vdev);
> > >
> > > +     enable_refill_work(vi);
> > > +
> > >       if (netif_running(vi->dev)) {
> > >               err = virtnet_open(vi->dev);
> > >               if (err)
> > > @@ -3535,6 +3565,7 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >       vdev->priv = vi;
> > >
> > >       INIT_WORK(&vi->config_work, virtnet_config_changed_work);
> > > +     spin_lock_init(&vi->refill_lock);
> > >
> > >       /* If we can receive ANY GSO packets, we must allocate large ones. */
> > >       if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> > > --
> > > 2.25.1
> >