Re: [RFC PATCH v2 0/5] TUN/VirtioNet USO features support.

[Jason Wang <jasowang@redhat.com>]

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On Tue, May 24, 2022 at 7:07 PM Andrew Melnichenko <andrew@daynix.com> wrote:
>
> Hi all,
>
> The issue is that host segments packets between guests on the same host.
> Tests show that it happens because SKB_GSO_DODGY skb offload in
> virtio_net_hdr_from_skb().
> To do segmentation you need to remove SKB_GSO_DODGY or add SKB_GSO_PARTIAL
> The solution with DODGY/PARTIAL offload looks like a dirty hack, so
> for now, I've lived it as it is for further investigation.

Ok, I managed to find the previous discussion. It looks to me the
reason is that __udp_gso_segment will segment dodgy packets
unconditionally.

I wonder if the attached patch works? (compile test only).

Thanks

>
>
> On Tue, May 17, 2022 at 9:32 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Thu, May 12, 2022 at 7:33 PM Andrew Melnychenko <andrew@daynix.com> wrote:
> > >
> > > Added new offloads for TUN devices TUN_F_USO4 and TUN_F_USO6.
> > > Technically they enable NETIF_F_GSO_UDP_L4
> > > (and only if USO4 & USO6 are set simultaneously).
> > > It allows to transmission of large UDP packets.
> > >
> > > Different features USO4 and USO6 are required for qemu where Windows guests can
> > > enable disable USO receives for IPv4 and IPv6 separately.
> > > On the other side, Linux can't really differentiate USO4 and USO6, for now.
> > > For now, to enable USO for TUN it requires enabling USO4 and USO6 together.
> > > In the future, there would be a mechanism to control UDP_L4 GSO separately.
> > >
> > > Test it WIP Qemu https://github.com/daynix/qemu/tree/Dev_USOv2
> > >
> > > New types for VirtioNet already on mailing:
> > > https://lists.oasis-open.org/archives/virtio-comment/202110/msg00010.html
> > >
> > > Also, there is a known issue with transmitting packages between two guests.
> >
> > Could you explain this more? It looks like a bug. (Or any pointer to
> > the discussion)
> >
> > Thanks
> >
> > > Without hacks with skb's GSO - packages are still segmented on the host's postrouting.
> > >
> > > Andrew (5):
> > >   uapi/linux/if_tun.h: Added new offload types for USO4/6.
> > >   driver/net/tun: Added features for USO.
> > >   uapi/linux/virtio_net.h: Added USO types.
> > >   linux/virtio_net.h: Support USO offload in vnet header.
> > >   drivers/net/virtio_net.c: Added USO support.
> > >
> > >  drivers/net/tap.c               | 10 ++++++++--
> > >  drivers/net/tun.c               |  8 +++++++-
> > >  drivers/net/virtio_net.c        | 19 +++++++++++++++----
> > >  include/linux/virtio_net.h      |  9 +++++++++
> > >  include/uapi/linux/if_tun.h     |  2 ++
> > >  include/uapi/linux/virtio_net.h |  4 ++++
> > >  6 files changed, 45 insertions(+), 7 deletions(-)
> > >
> > > --
> > > 2.35.1
> > >
> >
>

[-- Attachment #2: 0001-udp-allow-header-check-for-dodgy-GSO_UDP_L4-packets.patch --]
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From 4ced6ff3a8ea13b069dd3087ab22d252696e1def Mon Sep 17 00:00:00 2001
From: Jason Wang <jasowang@redhat.com>
Date: Thu, 26 May 2022 14:29:17 +0800
Subject: [PATCH] udp: allow header check for dodgy GSO_UDP_L4 packets
Content-type: text/plain

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 net/ipv4/udp_offload.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 6d1a4bec2614..9579886ce557 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -280,6 +280,15 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 	if (gso_skb->len <= sizeof(*uh) + mss)
 		return ERR_PTR(-EINVAL);
 
+	if (skb_gso_ok(gso_skb, features | NETIF_F_GSO_ROBUST)) {
+		/* Packet is from an untrusted source, reset gso_segs. */
+
+		skb_shinfo(gso_skb)->gso_segs = DIV_ROUND_UP(gso_skb->len, mss);
+
+		segs = NULL;
+		goto out;
+	}
+
 	skb_pull(gso_skb, sizeof(*uh));
 
 	/* clear destructor to avoid skb_segment assigning it to tail */
@@ -361,6 +370,7 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 		else
 			WARN_ON_ONCE(refcount_sub_and_test(-delta, &sk->sk_wmem_alloc));
 	}
+out:
 	return segs;
 }
 EXPORT_SYMBOL_GPL(__udp_gso_segment);
-- 
2.25.1