Wireguard & hw flow offload incompatibility

[Jason A. Donenfeld]

Hey Felix,

Per the below thread, I've been digging around trying to see what's
going on. Apparently packets are hitting a virtual network interface's
ndo_start_xmit with no dst when hardware offloading enabled. I assume
that the path is something along the lines of a packet coming in on
one of these hardware accelerated NICs and then being forwarded to the
wireguard interface, which expects the dst. I found your
ndo_flow_offload patchset, and I suspect that might have something to
do with this. Any insights on dsts disappearing in skbs?

Thanks,
Jason

On Tue, May 29, 2018 at 2:14 PM, Jason A. Donenfeld <Jason at zx2c4.com> wrote:
> Hi Jaap,
>
> Thanks for the clarification. I downloaded the binary for that
> hardware and triaged where the bug occurs [1]. This patch [2] should
> probably fix it, but I'm rather surprised to see situations in which a
> skb is missing a dst entry in ndo_start_xmit; this might point to
> deeper kernel bugs in this hardware offloading feature, or some
> alternative mechanism for routing being used when hardware offloading
> is on. So I'm hesitant to merge this just yet, because perhaps this is
> better handled in the compat layer, if it is in fact vendor silliness.
> Do you have a link to the kernel source of these boxes? I'd like to
> see what exactly the vendor is doing. And if you could try [2] and see
> if that still crashes, this would be most appreciated.
>
> Thanks,
> Jason
>
> [1] https://data.zx2c4.com/openwrt-mips-offloading-bug.png
> [2] https://א.cc/Am4tZ0n8
>
> On Tue, May 29, 2018 at 1:59 PM, Jaap Buurman <jaapbuurman at gmail.com> wrote:
>> Dear Jason,
>>
>> This isn't a regression. This is simply the first time this has been
>> observed. (hw) flow offload is a new feature, and hence this
>> interaction with wireguard is also new.
>>
>> Yours sincerely,
>>
>> Jaap
>>
>> On Tue, May 29, 2018 at 1:54 PM, Jason A. Donenfeld <Jason at zx2c4.com> wrote:
>>> Hi Jaap,
>>>
>>> Thanks for the report. Is this a _new_ bug in _new_ version of
>>> WireGuard that wasn't there before. Or is this the first time you've
>>> observed this?
>>>
>>> Thanks,
>>> Jason
>
> ============ Original Mail ==============
>
>> Dear all,
>>
>> When running a wireguard interface on the latest Lede master branch,
>> the router will crash as soon as traffic hits the wireguard interface
>> while (hw) flow offloading is enabled. I am not sure whether this is a
>> bug with wireguard, hw flow offload, both or neither, so I am
>> reporting the bug to both mailinglists. A more detailed description
>> plus a properly formatted stack trace can be found on Lede's bug
>> tracker: https://bugs.openwrt.org/index.php?do=details&task_id=1539
>>
>> If you require any additional information, please do not hesitate to
>> contact me. Thank you very much in advance.
>>
>> Yours sincerely,
>>
>> Jaap Buurman