[PATCH 5/6] vhost_net: fix use after free of vq->ubufs

[Jason Wang <jasowang@redhat.com>]

When zerocopy socket is used, ubufs pointer were used in handle_tx()
without any validation. This would cause NULL pointer deference after
it has been freed in vhost_net_set_backend(). Fix this by check the
pointer before using it.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/net.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index f0da2c3..29abd65 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -163,10 +163,15 @@ static void handle_tx(struct vhost_net *net)
 	mutex_lock(&vq->mutex);
 	vhost_disable_notify(&net->dev, vq);
 
+	zcopy = vhost_sock_zcopy(sock);
+	if (zcopy && !vq->ubufs) {
+		mutex_unlock(&vq->mutex);
+		return;
+	}
+
 	if (wmem < sock->sk->sk_sndbuf / 2)
 		tx_poll_stop(net);
 	hdr_size = vq->vhost_hlen;
-	zcopy = vhost_sock_zcopy(sock);
 
 	for (;;) {
 		/* Release DMAs done buffers first */