Re: [PATCH net-next 0/4] more virtio-net csum hardening

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Oct 13, 2026 at 08:41:19AM -0600, Willem de Bruijn wrote:
> On Tue, Oct 13, 2026 at 4:58 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > Allowing untrusted hardware to specify csum start/offset for
> > CHECKSUM_PARTIAL was not a good idea, because, if it edits the packet
> > outside the actual checksum, and depending on the setup, the networking
> > stack could be looking at the packet both before and after the edit, and
> > seeing different results.
> >
> > Previously, commit 6785011f8b16 ("ipv4: validate checksum_start before
> > completing checksum") validated all known instances where this
> > causes the most grief, but the real fix is to make sure
> > that either only actual checksum fields are ever edited,
> > or the checksum is completed before the net stack looks at it,
> > so it is always consistent.
> 
> +1 on the general approach of performing the checksum offload at
> input, unless the input can easily be validated to be one of a few
> common protocols. That greatly reduces the risk vs my previous attempt
> at trying to drop.
> 
> Since we do not know the full extent of grief, I think this too should
> go to net and stable.

I think it needs a bit more testing to be frank, I do not see it
wait months out of the tree. So if this lands in next before the
merge window, we are good I think. If we miss that I will target net.


> That would mean initially a single patch that
> touches as few files as possible. The helper function in
> include/linux/ip.h and conversion of existing open coded parsers to
> use that can follow up later in net-next.

I don't see the value to be frank.
What moving code between files accomplishes, I donnu.
Squashing things surely makes review harder?
Does your backporting system really struggle with trivial
dependencies like this?

I can drop patch 2 and will if I am targeting net.

> 
> > This basically does this: checksum at ingress, except in a narrow list
> > of specified known good cases.
> >
> > Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")
> >
> > Michael S. Tsirkin (4):
> >   net: add ip4_parse()
> >   net: use ip4_parse() in receive validation
> >   net: resolve uncommon partial checksums at ingress
> >   net: account for ingress-resolved virtio net hdr state