netdev - Re: [PATCH net v3 0/3] net/sched: fix actions reading the network header in case of QinQ packets

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]

Date:   Wed, 5 Jun 2019 18:42:20 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eli Britstein <elibr@...lanox.com>
Cc:     Davide Caratti <dcaratti@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        "David S . Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Shuang Li <shuali@...hat.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH net v3 0/3] net/sched: fix actions reading the network
 header in case of QinQ packets

On Tue, Jun 4, 2019 at 11:19 AM Eli Britstein <elibr@...lanox.com> wrote:
>
>
> On 6/4/2019 8:55 PM, Cong Wang wrote:
> > On Sat, Jun 1, 2019 at 9:22 PM Eli Britstein <elibr@...lanox.com> wrote:
> >> I think that's because QinQ, or VLAN is not an encapsulation. There is
> >> no outer/inner packets, and if you want to mangle fields in the packet
> >> you can do it and the result is well-defined.
> > Sort of, perhaps VLAN tags are too short to be called as an
> > encapsulation, my point is that it still needs some endpoints to push
> > or pop the tags, in a similar way we do encap/decap.
> >
> >
> >> BTW, the motivation for my fix was a use case were 2 VGT VMs
> >> communicating by OVS failed. Since OVS sees the same VLAN tag, it
> >> doesn't add explicit VLAN pop/push actions (i.e pop, mangle, push). If
> >> you force explicit pop/mangle/push you will break such applications.
> >  From what you said, it seems act_csum is in the middle of packet
> > receive/transmit path. So, which is the one pops the VLAN tags in
> > this scenario? If the VM's are the endpoints, why not use act_csum
> > there?
>
> In a switchdev mode, we can passthru the VFs to VMs, and have their
> representors in the host, enabling us to manipulate the HW eswitch
> without knowledge of the VMs.
>
> To simplify it, consider the following setup:
>
> v1a <-> v1b and v2a <-> v2b are veth pairs.
>
> Now, we configure v1a.20 and v2a.20 as VLAN devices over v1a/v2a
> respectively (and put the "a" devs in separate namespaces).
>
> The TC rules are on the "b" devs, for example:
>
> tc filter add dev v1b ... action pedit ... action csum ... action
> redirect dev v2b
>
> Now, ping from v1a.20 to v1b.20. The namespaces transmit/receive tagged
> packets, and are not aware of the packet manipulation (and the required
> act_csum).

This is what I said, v1b is not the endpoint which pops the vlan tag,
v1b.20 is. So, why not simply move at least the csum action to
v1b.20? With that, you can still filter and redirect packets on v1b,
you still even modify it too, just defer the checksum fixup to the
endpoint.

And to be fair, if this case is a valid concern, so is VXLAN case,
just replace v1a.20 and v2a.20 with VXLAN tunnels. If you modify
the inner header, you have to fixup the checksum in the outer
UDP header.

Thanks.