Re: [PATCH V2] virtio-net: fix the race between refill work and close

From: Jason Wang
Date: Thu Jun 30 2022 - 02:32:15 EST

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On Thu, Jun 30, 2022 at 2:26 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, 30 Jun 2022 14:07:52 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > On Thu, Jun 30, 2022 at 10:22 AM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
> > >
> > > On Thu, 30 Jun 2022 10:08:04 +0800, Jason Wang <jasowang@xxxxxxxxxx> 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].
> > >
> > >
> > > Can you explain in more detail how this happened?
> > >
> > > napi_disable() is normally called after cancel_delayed_work_sync(). This ensures
> > > that all napi callbacks will end, and the new napi_disable() will wait.
> > > There will be no re-enable napi.
> >
> > An rx interrupt that may come between after the cancel_delayed_work()
> > but before the napi_disable(). It schedules a refill_work that may run
> > after the napi_disable() in virtnet_close().
>
> Yes
>
>
> >
> > >
> > > So I guess the use-after-free is caused by refill_work being called after
> > > dev/vi/napi is released. In this way, we can just call
> > > cancel_delayed_work_sync() after napi_disalbe().
> >
> > So the refill_work can re-enable the NAPI when it is run after
> > napi_disable() in this case.
>
>
> Since napi_disable() has been called in virtnet_close(), it will get stuck when
> napi_disable() in refill_work().

Right because e.g NAPIF_STATE_SCHED has been set by napi_disable() before.

> I think use-after-free is because vi/napi etc.
> have been released, refill_work() going to access again causes an exception.

Yes, this is the use-after-free I mentioned above.

>
> napi will not be re-enable.
>
> I would like to call cancel_delayed_work_sync() after napi_disable()
> to solve this problem. But this also has a problem, refill_work() can get stuck
> on napi_disable() and cannot exit. In this way, we want napi_disable() to check
> that the current state is disabled and exit directly.

Not sure this is a good design and it doesn't fit for -stable.

I think the design of NAPI is to pair napi_enable() and napi_disable()
instead of allowing napi_disable() to be called twice.

Thanks

>
> Thanks.
>
>
> >
> > Thanks
> >
> >
> > >
> > > Thanks.
> > >
> > > >
> > > > 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@xxxxxxxxxx>
> > > > ---
> > > > drivers/net/virtio_net.c | 38 ++++++++++++++++++++++++++++++++++++--
> > > > 1 file changed, 36 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index db05b5e930be..21bf1e5c81ef 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? */
> > > > + bool refill_work_enabled;
> > > > +
> > > > + /* The lock to synchronize the access to refill_work_enabled */
> > > > + 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(&vi->refill_lock);
> > > > + vi->refill_work_enabled = true;
> > > > + spin_unlock(&vi->refill_lock);
> > > > +}
> > > > +
> > > > +static void disable_refill_work(struct virtnet_info *vi)
> > > > +{
> > > > + spin_lock(&vi->refill_lock);
> > > > + vi->refill_work_enabled = false;
> > > > + spin_unlock(&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);
> > > >
> > > > @@ -2776,6 +2804,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
> > > > netif_tx_lock_bh(vi->dev);
> > > > netif_device_detach(vi->dev);
> > > > netif_tx_unlock_bh(vi->dev);
> > > > + /* 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);
> > > >
> > > > if (netif_running(vi->dev)) {
> > > > @@ -2799,6 +2830,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
> > > >
> > > > virtio_device_ready(vdev);
> > > >
> > > > + enable_refill_work(vi);
> > > > +
> > > > if (netif_running(vi->dev)) {
> > > > for (i = 0; i < vi->curr_queue_pairs; i++)
> > > > if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> > > > @@ -3548,6 +3581,7 @@ 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
> > > >
> > >
> >
>

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Next in thread: Jakub Kicinski: "Re: [PATCH V2] virtio-net: fix the race between refill work and close"
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