netdev - Re: [PATCH net v4 3/4] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST

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: <20251110110751-mutt-send-email-mst@kernel.org>
Date: Mon, 10 Nov 2025 11:10:43 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org,
	Eugenio Pérez <eperezma@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Heng Qi <hengqi@...ux.alibaba.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Jiri Pirko <jiri@...nulli.us>,
	Alvaro Karsz <alvaro.karsz@...id-run.com>,
	virtualization@...ts.linux.dev
Subject: Re: [PATCH net v4 3/4] virtio-net: correct hdr_len handling for
 VIRTIO_NET_F_GUEST_HDRLEN

On Mon, Nov 10, 2025 at 03:39:50PM +0800, Jason Wang wrote:
> On Mon, Nov 10, 2025 at 3:27 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > On Mon, Nov 10, 2025 at 03:16:08PM +0800, Jason Wang wrote:
> > > On Mon, Nov 10, 2025 at 5:41 AM Michael S. Tsirkin <mst@...hat.com> wrote:
> > > >
> > > > On Thu, Oct 30, 2025 at 10:53:01AM +0800, Jason Wang wrote:
> > > > > On Wed, Oct 29, 2025 at 11:09 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > > > > >
> > > > > > The commit be50da3e9d4a ("net: virtio_net: implement exact header length
> > > > > > guest feature") introduces support for the VIRTIO_NET_F_GUEST_HDRLEN
> > > > > > feature in virtio-net.
> > > > > >
> > > > > > This feature requires virtio-net to set hdr_len to the actual header
> > > > > > length of the packet when transmitting, the number of
> > > > > > bytes from the start of the packet to the beginning of the
> > > > > > transport-layer payload.
> > > > > >
> > > > > > However, in practice, hdr_len was being set using skb_headlen(skb),
> > > > > > which is clearly incorrect. This commit fixes that issue.
> > > > >
> > > > > I still think it would be more safe to check the feature
> > > >
> > > > which feature VIRTIO_NET_F_GUEST_HDRLEN ?
> > > >
> > >
> > > Yes.
> > >
> > > Thanks
> >
> > Seems more conservative for sure, though an extra mode to maintain isn't
> > great. Hmm?
> 
> Considering it's not a lot of code, it might be worth it to reduce the risk.
> 
> But I'm fine if you think we can go with this patch.
> 
> Thanks

hard to say what does "not a lot of code" mean here.
but generally if VIRTIO_NET_F_GUEST_HDRLEN is not set
just doing a quick skb_headlen and not poking at
the transport things sounds like a win.

I'd like to at least see the patch along the lines you propose,
and we will judge if it's too much mess to support.


> >
> > --
> > MST
> >