vsock: Update rx_bytes on read_skb()

Make sure virtio_transport_inc_rx_pkt() and virtio_transport_dec_rx_pkt()
calls are balanced (i.e. virtio_vsock_sock::rx_bytes doesn't lie) after
vsock_transport::read_skb().

While here, also inform the peer that we've freed up space and it has more
credit.

Failing to update rx_bytes after packet is dequeued leads to a warning on
SOCK_STREAM recv():

[  233.396654] rx_queue is empty, but rx_bytes is non-zero
[  233.396702] WARNING: CPU: 11 PID: 40601 at net/vmw_vsock/virtio_transport_common.c:589

Fixes: 634f1a7110b4 ("vsock: support sockmap")
Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20241013-vsock-fixes-for-redir-v2-2-d6577bbfe742@rbox.co

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 884ee128851e5ce8b01c78fcb95a408986f62936..2e5ad96825cc0988c9e1b3f8a8bfcff2ef00a2b2 100644 (file)
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -1707,6 +1707,7 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
 {
        struct virtio_vsock_sock *vvs = vsk->trans;
        struct sock *sk = sk_vsock(vsk);
+       struct virtio_vsock_hdr *hdr;
        struct sk_buff *skb;
        int off = 0;
        int err;
@@ -1716,10 +1717,16 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
         * works for types other than dgrams.
         */
        skb = __skb_recv_datagram(sk, &vvs->rx_queue, MSG_DONTWAIT, &off, &err);
+       if (!skb) {
+               spin_unlock_bh(&vvs->rx_lock);
+               return err;
+       }
+
+       hdr = virtio_vsock_hdr(skb);
+       virtio_transport_dec_rx_pkt(vvs, le32_to_cpu(hdr->len));
        spin_unlock_bh(&vvs->rx_lock);
 
-       if (!skb)
-               return err;
+       virtio_transport_send_credit_update(vsk);
 
        return recv_actor(sk, skb);
 }