On Tue, Oct 13, 2026 at 12:41 PM Michael S. Tsirkin <[email protected]> wrote:
>
> 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 <[email protected]> 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.
Good. This is not about "my" backporting, but upstream stable.
Refactor patches do not belong there.
Since patch 3 might have to be backported in the future if a serious
abuse surfaces, even if you now land it in net-next, it is better to
not depend on other patches.
> >
> > > 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
>
