netdev - Re: [PATCH v4 net-next 7/8] tun: enable gso over UDP tunnel support.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <bc579418-646f-4ccc-bf9c-976b264c4da2@daynix.com>
Date: Fri, 20 Jun 2025 00:46:20 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Jason Wang <jasowang@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, "Michael S. Tsirkin" <mst@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Yuri Benditovich <yuri.benditovich@...nix.com>
Subject: Re: [PATCH v4 net-next 7/8] tun: enable gso over UDP tunnel support.

On 2025/06/19 23:52, Paolo Abeni wrote:
> On 6/19/25 4:42 PM, Akihiko Odaki wrote:
>> On 2025/06/18 1:12, Paolo Abeni wrote:
>>> @@ -1721,7 +1733,12 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>>>    	if (tun->flags & IFF_VNET_HDR) {
>>>    		int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
>>>    
>>> -		hdr_len = tun_vnet_hdr_get(vnet_hdr_sz, tun->flags, from, &gso);
>>> +		if (vnet_hdr_sz >= TUN_VNET_TNL_SIZE)
>>> +			features = NETIF_F_GSO_UDP_TUNNEL |
>>> +				   NETIF_F_GSO_UDP_TUNNEL_CSUM;
>>
>> I think you should use tun->set_features instead of tun->vnet_hdr_sz to
>> tell if these features are enabled.
> 
> This is the guest -> host direction. tun->set_features refers to the
> opposite one. The problem is that tun is not aware of the features
> negotiated in the guest -> host direction.
> 
> The current status (for baremetal/plain offload) is allowing any known
> feature the other side send - if the virtio header is consistent.
> This code follows a similar schema.
> 
> Note that using 'tun->set_features' instead of 'vnet_hdr_sz' the tun
> driver will drop all the (legit) GSO over UDP packet sent by the guest
> when the VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO has been negotiated and
> VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO has not.

This explanation makes sense. In that case I suggest:
- creating a new function named tun_vnet_hdr_tnl_get() and
- passing vnet_hdr_sz to tun_vnet_hdr_tnl_to_skb()

tun_vnet.h contains the virtio-related logic for better code 
organization and reuse with tap.c. tap.c can reuse the conditionals on 
vnet_hdr_sz when tap.c gains the UDP tunneling support.