Re: [PATCH net] vsock: account only unread bytes in read_skb()

[Luigi Leonardi <leonardi@redhat.com>]

Hi,

what about using `vsock/virtio` instead of `vsock`? We are changing
just the virtio parts of vsock.

On Thu, Oct 01, 2026 at 09:15:41PM +0900, Daehyeon Ko wrote:
>After a partial stream receive, rx_bytes tracks the unread suffix while
>buf_used and peer credit still cover the whole packet.
>virtio_transport_read_skb() dequeues that packet but passes pkt_len for
>both counters, underflowing rx_bytes.
>
>On a connected CID_LOCAL stream with an SK_SKB verdict, a 40-byte read
>from a 100-byte packet made SIOCINQ report -40, an empty recv return
>ELOOP, and poll report the empty socket readable.  After verdict detach,
>receiving 40 bytes wrapped the counter to zero and hid those queued bytes
>until one more byte arrived.  The fixed run kept the counter balanced
>and exposed all queued data immediately.
>
>Subtract only skb->len minus the VSOCK offset from rx_bytes.  Retain the
>full packet length for buf_used and peer credit.
>
>Fixes: 45ca7e9f0730 ("vsock/virtio: fix `rx_bytes` accounting for stream sockets")
>Cc: stable@vger.kernel.org
>Assisted-by: LLM
>Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
>---
> net/vmw_vsock/virtio_transport_common.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index f225f53ed4bab..1e762a480df49 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -1927,6 +1927,7 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
> 	struct sock *sk = sk_vsock(vsk);
> 	struct virtio_vsock_hdr *hdr;
> 	struct sk_buff *skb;
>+	u32 bytes_read;
> 	u32 pkt_len;
> 	int off = 0;
> 	int err;
>@@ -1946,7 +1947,8 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
> 		vvs->msg_count--;
>
> 	pkt_len = le32_to_cpu(hdr->len);
>-	virtio_transport_dec_rx_pkt(vvs, pkt_len, pkt_len);

maybe it's worth adding a comment? not a strong opinion.

>+	bytes_read = skb->len - VIRTIO_VSOCK_SKB_CB(skb)->offset;
>+	virtio_transport_dec_rx_pkt(vvs, bytes_read, pkt_len);
> 	spin_unlock_bh(&vvs->rx_lock);
>
> 	virtio_transport_send_credit_update(vsk);
>
>base-commit: e23a64eb244356ee47c0620f0722d51bd88db522
>-- 
>2.55.0
>

code LGTM!

Reviewed-by: Luigi Leonardi <leonardi@redhat.com>

Thanks,
Luigi