Re: [PATCH net-next v5] udp:allow UDP cmsghdrs through io_uring

[Soheil Hassas Yeganeh <soheil@google.com>]

On Wed, Dec 16, 2020 at 5:56 PM Victor Stewart <v@nametag.social> wrote:
>
> This patch adds PROTO_CMSG_DATA_ONLY to inet_dgram_ops and inet6_dgram_ops so that UDP_SEGMENT (GSO) and UDP_GRO can be used through io_uring.
>
> GSO and GRO are vital to bring QUIC servers on par with TCP throughputs, and together offer a higher
> throughput gain than io_uring alone (rate of data transit
> considering), thus io_uring is presently the lesser performance choice.
>
> RE http://vger.kernel.org/lpc_net2018_talks/willemdebruijn-lpc2018-udpgso-paper-DRAFT-1.pdf,
> GSO is about +~63% and GRO +~82%.
>
> this patch closes that loophole.
>
> Signed-off-by: Victor Stewart <v@nametag.social>

Acked-by: Soheil Hassas Yeganeh <soheil@google.com>

Thanks for adding this! I audied the code and couldn't find an
escalation path.  +Jann could you please double check?

> ---
>  net/ipv4/af_inet.c  | 1 +
>  net/ipv6/af_inet6.c | 1 +
>  net/socket.c        | 8 +++++---
>  3 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index b7260c8cef2e..c9fd5e7cfd6e 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1052,6 +1052,7 @@ EXPORT_SYMBOL(inet_stream_ops);
>
>  const struct proto_ops inet_dgram_ops = {
>         .family            = PF_INET,
> +       .flags             = PROTO_CMSG_DATA_ONLY,
>         .owner             = THIS_MODULE,
>         .release           = inet_release,
>         .bind              = inet_bind,
> diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> index e648fbebb167..560f45009d06 100644
> --- a/net/ipv6/af_inet6.c
> +++ b/net/ipv6/af_inet6.c
> @@ -695,6 +695,7 @@ const struct proto_ops inet6_stream_ops = {
>
>  const struct proto_ops inet6_dgram_ops = {
>         .family            = PF_INET6,
> +       .flags             = PROTO_CMSG_DATA_ONLY,
>         .owner             = THIS_MODULE,
>         .release           = inet6_release,
>         .bind              = inet6_bind,
> diff --git a/net/socket.c b/net/socket.c
> index 6e6cccc2104f..6995835d6355 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2416,9 +2416,11 @@ static int ___sys_sendmsg(struct socket *sock, struct user_msghdr __user *msg,
>  long __sys_sendmsg_sock(struct socket *sock, struct msghdr *msg,
>                         unsigned int flags)
>  {
> -       /* disallow ancillary data requests from this path */
> -       if (msg->msg_control || msg->msg_controllen)
> -               return -EINVAL;
> +       if (msg->msg_control || msg->msg_controllen) {
> +               /* disallow ancillary data reqs unless cmsg is plain data */
> +               if (!(sock->ops->flags & PROTO_CMSG_DATA_ONLY))
> +                       return -EINVAL;
> +       }
>
>         return ____sys_sendmsg(sock, msg, flags, NULL, 0);
>  }
> --
> 2.26.2
>