[PATCH 0/1] vdpa: Fix possible use-after-free for VirtQueueElement

[Hawkins Jiawei <yin31149@gmail.com>]

This patch fixes the problem that vhost_vdpa_net_handle_ctrl_avail()
mistakenly frees the `elem`, even if it fails to forward the
CVQ command to vdpa device. This can result in a use-after-free

TestStep
========
1. test the patch using vp-vdpa device
  - For L0 guest, boot QEMU with virtio-net-pci net device with `ctrl_vq`
feature on, something like:
      -device virtio-net-pci,rx_queue_size=256,tx_queue_size=256,
iommu_platform=on,ctrl_vq=on,...

  - For L1 guest, apply the patch series, then apply an addtional
patch to make the vhost_vdpa_net_handle_ctrl_avail() fails to process
the CVQ command as below:

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index d8f37694ac..1f22355a41 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -797,7 +797,8 @@ static int vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
         dev_written = sizeof(status);
         *s->status = VIRTIO_NET_OK;
     } else {
-        dev_written = vhost_vdpa_net_cvq_add(s, out.iov_len, sizeof(status));
+        //dev_written = vhost_vdpa_net_cvq_add(s, out.iov_len, sizeof(status));
+        dev_written = -EINVAL;
         if (unlikely(dev_written < 0)) {
             goto out;
         }

start QEMU with vdpa device with svq mode and enable the `ctrl_vq`
feature on, something like:
      -netdev type=vhost-vdpa,x-svq=true,...
      -device virtio-net-pci,ctrl_vq=on,...

With this series, QEMU should not trigger any error or warning.
Without this series, QEMU should fail with
"free(): double free detected in tcache 2".

Hawkins Jiawei (1):
  vdpa: Fix possible use-after-free for VirtQueueElement

 net/vhost-vdpa.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

-- 
2.25.1