Re: [PATCH RFC net-next v5 07/14] virtio/vsock: add common datagram send path

[Arseniy Krasnov <oxffffaa@gmail.com>]

On 19.07.2023 03:50, Bobby Eshleman wrote:
> This commit implements the common function
> virtio_transport_dgram_enqueue for enqueueing datagrams. It does not add
> usage in either vhost or virtio yet.
> 
> Signed-off-by: Bobby Eshleman <bobby.eshleman@bytedance.com>
> ---
>  net/vmw_vsock/virtio_transport_common.c | 76 ++++++++++++++++++++++++++++++++-
>  1 file changed, 75 insertions(+), 1 deletion(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index ffcbdd77feaa..3bfaff758433 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -819,7 +819,81 @@ virtio_transport_dgram_enqueue(struct vsock_sock *vsk,
>  			       struct msghdr *msg,
>  			       size_t dgram_len)
>  {
> -	return -EOPNOTSUPP;
> +	/* Here we are only using the info struct to retain style uniformity
> +	 * and to ease future refactoring and merging.
> +	 */
> +	struct virtio_vsock_pkt_info info_stack = {
> +		.op = VIRTIO_VSOCK_OP_RW,
> +		.msg = msg,
> +		.vsk = vsk,
> +		.type = VIRTIO_VSOCK_TYPE_DGRAM,
> +	};
> +	const struct virtio_transport *t_ops;
> +	struct virtio_vsock_pkt_info *info;
> +	struct sock *sk = sk_vsock(vsk);
> +	struct virtio_vsock_hdr *hdr;
> +	u32 src_cid, src_port;
> +	struct sk_buff *skb;
> +	void *payload;
> +	int noblock;
> +	int err;
> +
> +	info = &info_stack;

I think 'info' assignment could be moved below, to the place where it is used
first time.

> +
> +	if (dgram_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
> +		return -EMSGSIZE;
> +
> +	t_ops = virtio_transport_get_ops(vsk);
> +	if (unlikely(!t_ops))
> +		return -EFAULT;
> +
> +	/* Unlike some of our other sending functions, this function is not
> +	 * intended for use without a msghdr.
> +	 */
> +	if (WARN_ONCE(!msg, "vsock dgram bug: no msghdr found for dgram enqueue\n"))
> +		return -EFAULT;

Sorry, but is that possible? I thought 'msg' is always provided by general socket layer (e.g. before
af_vsock.c code) and can't be NULL for DGRAM. Please correct me if i'm wrong.

Also I see, that in af_vsock.c , 'vsock_dgram_sendmsg()' dereferences 'msg' for checking MSG_OOB without any
checks (before calling transport callback - this function in case of virtio). So I think if we want to keep
this type of check - such check must be placed in af_vsock.c or somewhere before first dereference of this pointer.

> +
> +	noblock = msg->msg_flags & MSG_DONTWAIT;
> +
> +	/* Use sock_alloc_send_skb to throttle by sk_sndbuf. This helps avoid
> +	 * triggering the OOM.
> +	 */
> +	skb = sock_alloc_send_skb(sk, dgram_len + VIRTIO_VSOCK_SKB_HEADROOM,
> +				  noblock, &err);
> +	if (!skb)
> +		return err;
> +
> +	skb_reserve(skb, VIRTIO_VSOCK_SKB_HEADROOM);
> +
> +	src_cid = t_ops->transport.get_local_cid();
> +	src_port = vsk->local_addr.svm_port;
> +
> +	hdr = virtio_vsock_hdr(skb);
> +	hdr->type	= cpu_to_le16(info->type);
> +	hdr->op		= cpu_to_le16(info->op);
> +	hdr->src_cid	= cpu_to_le64(src_cid);
> +	hdr->dst_cid	= cpu_to_le64(remote_addr->svm_cid);
> +	hdr->src_port	= cpu_to_le32(src_port);
> +	hdr->dst_port	= cpu_to_le32(remote_addr->svm_port);
> +	hdr->flags	= cpu_to_le32(info->flags);
> +	hdr->len	= cpu_to_le32(dgram_len);
> +
> +	skb_set_owner_w(skb, sk);
> +
> +	payload = skb_put(skb, dgram_len);
> +	err = memcpy_from_msg(payload, msg, dgram_len);
> +	if (err)
> +		return err;

Do we need free allocated skb here ?

> +
> +	trace_virtio_transport_alloc_pkt(src_cid, src_port,
> +					 remote_addr->svm_cid,
> +					 remote_addr->svm_port,
> +					 dgram_len,
> +					 info->type,
> +					 info->op,
> +					 0);
> +
> +	return t_ops->send_pkt(skb);
>  }
>  EXPORT_SYMBOL_GPL(virtio_transport_dgram_enqueue);
>  
> 

Thanks, Arseniy