Re: [PATCH V6] virtio-net: fix the race between refill work and close

[Jason Wang]

On Mon, Jul 25, 2022 at 3:22 PM 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].
>
> 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.

In case this is not too late, the patch is for -net. (otherwise i can repost).

Thanks

>
> [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 | 37 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 356cf8dd4164..ec8e1b3108c3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -242,9 +242,15 @@ struct virtnet_info {
>         /* Packet virtio header size */
>         u8 hdr_len;
>
> -       /* Work struct for refilling if we run low on memory. */
> +       /* Work struct for delayed refilling if we run low on memory. */
>         struct delayed_work refill;
>
> +       /* Is delayed refill enabled? */
> +       bool refill_enabled;
> +
> +       /* The lock to synchronize the access to refill_enabled */
> +       spinlock_t refill_lock;
> +
>         /* Work struct for config space updates */
>         struct work_struct config_work;
>
> @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
>         return p;
>  }
>
> +static void enable_delayed_refill(struct virtnet_info *vi)
> +{
> +       spin_lock_bh(&vi->refill_lock);
> +       vi->refill_enabled = true;
> +       spin_unlock_bh(&vi->refill_lock);
> +}
> +
> +static void disable_delayed_refill(struct virtnet_info *vi)
> +{
> +       spin_lock_bh(&vi->refill_lock);
> +       vi->refill_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_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_delayed_refill(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_delayed_refill(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_delayed_refill(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
>