On Wed, Jun 29, 2022 at 04:36:12PM +0800, Jason Wang wrote:

On Wed, Jun 29, 2022 at 3:29 PM Michael S. Tsirkin [off-list ref] wrote:

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On Tue, Jun 28, 2022 at 05:03:24PM +0800, Jason Wang wrote:

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We try using cancel_delayed_work_sync() to prevent the work from
enabling NAPI. This is insufficient since we don't disable the the
source the scheduling

can't parse this sentence

I actually meant "we don't disable the source of the refill work scheduling".

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of the refill work. This means an NAPI

what do you mean "an NAPI"? a NAPI poll callback?

Yes.

pls post with a fixed log then.

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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>
---
 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) ||

Can't say I love all the extra state but oh well.

I couldn't find a better way. The tricky part is that NAPI and refill
can schedule each other so we need a third state.

Thanks

I wonder whether we can add a napi flag that says going away
do not schedule, and have napi_enable/napi_disable fail then.

quoted

quoted

--
2.25.1