Re: [PATCH net-next v2] net: openvswitch: fix uAPI incompatibility with existing user space

[Eelco Chaudron]

On 12 May 2022, at 12:08, Vlad Buslov wrote:

> On Thu 12 May 2022 at 12:19, Eelco Chaudron <echaudro@xxxxxxxxxx> wrote:
>> On 7 Apr 2022, at 12:22, Ilya Maximets wrote:
>>
>>> On 4/7/22 10:02, Vlad Buslov wrote:
>>>> On Mon 14 Mar 2022 at 20:40, Ilya Maximets <i.maximets@xxxxxxx> wrote:
>>>>> On 3/14/22 19:33, Roi Dayan wrote:
>>>>>>
>>>>>>
>>>>>> On 2022-03-10 8:44 PM, Aaron Conole wrote:
>>>>>>> Ilya Maximets <i.maximets@xxxxxxx> writes:
>>>>>>>
>>>>>>>> Few years ago OVS user space made a strange choice in the commit [1]
>>>>>>>> to define types only valid for the user space inside the copy of a
>>>>>>>> kernel uAPI header.  '#ifndef __KERNEL__' and another attribute was
>>>>>>>> added later.
>>>>>>>>
>>>>>>>> This leads to the inevitable clash between user space and kernel types
>>>>>>>> when the kernel uAPI is extended.  The issue was unveiled with the
>>>>>>>> addition of a new type for IPv6 extension header in kernel uAPI.
>>>>>>>>
>>>>>>>> When kernel provides the OVS_KEY_ATTR_IPV6_EXTHDRS attribute to the
>>>>>>>> older user space application, application tries to parse it as
>>>>>>>> OVS_KEY_ATTR_PACKET_TYPE and discards the whole netlink message as
>>>>>>>> malformed.  Since OVS_KEY_ATTR_IPV6_EXTHDRS is supplied along with
>>>>>>>> every IPv6 packet that goes to the user space, IPv6 support is fully
>>>>>>>> broken.
>>>>>>>>
>>>>>>>> Fixing that by bringing these user space attributes to the kernel
>>>>>>>> uAPI to avoid the clash.  Strictly speaking this is not the problem
>>>>>>>> of the kernel uAPI, but changing it is the only way to avoid breakage
>>>>>>>> of the older user space applications at this point.
>>>>>>>>
>>>>>>>> These 2 types are explicitly rejected now since they should not be
>>>>>>>> passed to the kernel.  Additionally, OVS_KEY_ATTR_TUNNEL_INFO moved
>>>>>>>> out from the '#ifdef __KERNEL__' as there is no good reason to hide
>>>>>>>> it from the userspace.  And it's also explicitly rejected now, because
>>>>>>>> it's for in-kernel use only.
>>>>>>>>
>>>>>>>> Comments with warnings were added to avoid the problem coming back.
>>>>>>>>
>>>>>>>> (1 << type) converted to (1ULL << type) to avoid integer overflow on
>>>>>>>> OVS_KEY_ATTR_IPV6_EXTHDRS, since it equals 32 now.
>>>>>>>>
>>>>>>>>   [1] beb75a40fdc2 ("userspace: Switching of L3 packets in L2 pipeline")
>>>>>>>>
>>>>>>>> Fixes: 28a3f0601727 ("net: openvswitch: IPv6: Add IPv6 extension header support")
>>>>>>>> Link: https://lore.kernel.org/netdev/3adf00c7-fe65-3ef4-b6d7-6d8a0cad8a5f@xxxxxxxxxx
>>>>>>>> Link: https://github.com/openvswitch/ovs/commit/beb75a40fdc295bfd6521b0068b4cd12f6de507c
>>>>>>>> Reported-by: Roi Dayan <roid@xxxxxxxxxx>
>>>>>>>> Signed-off-by: Ilya Maximets <i.maximets@xxxxxxx>
>>>>>>>> ---
>>>>>>>
>>>>>>> Acked-by: Aaron Conole <aconole@xxxxxxxxxx>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> I got to check traffic with the fix and I do get some traffic
>>>>>> but something is broken. I didn't investigate much but the quick
>>>>>> test shows me rules are not offloaded and dumping ovs rules gives
>>>>>> error like this
>>>>>>
>>>>>> recirc_id(0),in_port(enp8s0f0_1),ct_state(-trk),eth(),eth_type(0x86dd),ipv6(frag=no)(bad
>>>>>> key length 2, expected -1)(00 00/(bad mask length 2, expected -1)(00 00),
>>>>>> packets:2453, bytes:211594, used:0.004s, flags:S., actions:ct,recirc(0x2)
>>>>>
>>>>> Such a dump is expected, because kernel parses fields that current
>>>>> userspace doesn't understand, and at the same time OVS by design is
>>>>> using kernel provided key/mask while installing datapath rules, IIRC.
>>>>> It should be possible to make these dumps a bit more friendly though.
>>>>>
>>>>> For the offloading not working, see my comment in the v2 patch email
>>>>> I sent (top email of this thread).  In short, it's a problem in user
>>>>> space and it can not be fixed from the kernel side, unless we revert
>>>>> IPv6 extension header support and never add any new types, which is
>>>>> unreasonable.  I didn't test any actual offloading, but I had a
>>>>> successful run of 'make check-offloads' with my quick'n'dirty fix from
>>>>> the top email.
>>>>
>>>> Hi Ilya,
>>>>
>>>> I can confirm that with latest OvS master IPv6 rules offload still fails
>>>> without your pastebin code applied.
>>>>
>>>>>
>>>>> Since we're here:
>>>>>
>>>>> Toms, do you plan to submit user space patches for this feature?
>>>>
>>>> I see there is a patch from you that is supposed to fix compatibility
>>>> issues caused by this change in OvS d96d14b14733 ("openvswitch.h: Align
>>>> uAPI definition with the kernel."), but it doesn't fix offload for me
>>>> without pastebin patch.
>>>
>>> Yes.  OVS commit d96d14b14733 is intended to only fix the uAPI.
>>> Issue with offload is an OVS bug that should be fixed separately.
>>> The fix will also need to be backported to OVS stable branches.
>>>
>>>> Do you plan to merge that code into OvS or you
>>>> require some help from our side?
>>>
>>> I could do that, but I don't really have enough time.  So, if you
>>> can work on that fix, it would be great.  Note that comments inside
>>> the OVS's lib/odp-util.c:parse_key_and_mask_to_match() was blindly
>>> copied from the userspace datapath and are incorrect for the general
>>> case, so has to be fixed alongside the logic of that function.
>>
>> Tom or Vlad, are you working on this? Asking, as the release of a kernel with
>> Tom’s “net: openvswitch: IPv6: Add IPv6 extension header support” patch will
>> break OVS.
>>
>> //Eelco
>
> Hi Eelco,
>
> My simple fix for OvS was rejected and I don't have time to rework it at
> the moment.

That’s a pity, Tom do you maybe have time as your patch left OVS in this error state?

//Eelco