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SubjectRe: [PATCH] vsock/virtio: add support for MSG_PEEK
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On 9/26/19 11:23 AM, Matias Ezequiel Vara Larsen wrote:
> This patch adds support for MSG_PEEK. In such a case, packets are not
> removed from the rx_queue and credit updates are not sent.
>
> Signed-off-by: Matias Ezequiel Vara Larsen <matiasevara@gmail.com>
> ---
> net/vmw_vsock/virtio_transport_common.c | 50 +++++++++++++++++++++++++++++++--
> 1 file changed, 47 insertions(+), 3 deletions(-)
>
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 94cc0fa..938f2ed 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -264,6 +264,50 @@ static int virtio_transport_send_credit_update(struct vsock_sock *vsk,
> }
>
> static ssize_t
> +virtio_transport_stream_do_peek(struct vsock_sock *vsk,
> + struct msghdr *msg,
> + size_t len)
> +{
> + struct virtio_vsock_sock *vvs = vsk->trans;
> + struct virtio_vsock_pkt *pkt;
> + size_t bytes, total = 0;
> + int err = -EFAULT;
> +
> + spin_lock_bh(&vvs->rx_lock);
> +
> + list_for_each_entry(pkt, &vvs->rx_queue, list) {
> + if (total == len)
> + break;
> +
> + bytes = len - total;
> + if (bytes > pkt->len - pkt->off)
> + bytes = pkt->len - pkt->off;
> +
> + /* sk_lock is held by caller so no one else can dequeue.
> + * Unlock rx_lock since memcpy_to_msg() may sleep.
> + */
> + spin_unlock_bh(&vvs->rx_lock);
> +
> + err = memcpy_to_msg(msg, pkt->buf + pkt->off, bytes);
> + if (err)
> + goto out;
> +
> + spin_lock_bh(&vvs->rx_lock);
> +
> + total += bytes;
> + }
> +
> + spin_unlock_bh(&vvs->rx_lock);
> +
> + return total;
> +
> +out:
> + if (total)
> + err = total;
> + return err;
> +}
>

This seems buggy to me.

virtio_transport_recv_enqueue() seems to be able to add payload to the last packet in the queue.

The loop you wrote here would miss newly added chunks while the vvs->rx_lock spinlock has been released.

virtio_transport_stream_do_dequeue() is ok, because it makes sure pkt->off == pkt->len
before cleaning the packet from the queue.



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