From: Daniel Axtens <dja@axtens•net>
To: Pravin Shelar <pshelar@ovn•org>
Cc: Linux Kernel Network Developers <netdev@vger•kernel.org>,
Manish.Chopra@cavium•com, ovs dev <dev@openvswitch•org>
Subject: Re: [PATCH 0/3] Check gso_size of packets when forwarding
Date: Fri, 19 Jan 2018 22:58:42 +1100 [thread overview]
Message-ID: <871sim5abx.fsf@linkitivity.dja.id.au> (raw)
In-Reply-To: <CAOrHB_AOyuzaKU5JYv=N20jfBsFD+2QEzRBNcu9KtxiTVA4r5w@mail.gmail.com>
Pravin Shelar <pshelar@ovn•org> writes:
> On Thu, Jan 18, 2018 at 5:28 PM, Daniel Axtens <dja@axtens•net> wrote:
>> Pravin Shelar <pshelar@ovn•org> writes:
>>
>>> On Thu, Jan 18, 2018 at 5:08 AM, Daniel Axtens <dja@axtens•net> wrote:
>>>> Pravin Shelar <pshelar@ovn•org> writes:
>>>>
>>>>> On Mon, Jan 15, 2018 at 6:09 PM, Daniel Axtens <dja@axtens•net> wrote:
>>>>>> When regular packets are forwarded, we validate their size against the
>>>>>> MTU of the destination device. However, when GSO packets are
>>>>>> forwarded, we do not validate their size against the MTU. We
>>>>>> implicitly assume that when they are segmented, the resultant packets
>>>>>> will be correctly sized.
>>>>>>
>>>>>> This is not always the case.
>>>>>>
>>>>>> We observed a case where a packet received on an ibmveth device had a
>>>>>> GSO size of around 10kB. This was forwarded by Open vSwitch to a bnx2x
>>>>>> device, where it caused a firmware assert. This is described in detail
>>>>>> at [0] and was the genesis of this series. Rather than fixing it in
>>>>>> the driver, this series fixes the forwarding path.
>>>>>>
>>>>> Are there any other possible forwarding path in networking stack? TC
>>>>> is one subsystem that could forward such a packet to the bnx2x device,
>>>>> how is that handled ?
>>>>
>>>> So far I have only looked at bridges, openvswitch and macvlan. In
>>>> general, if the code uses dev_forward_skb() it should automatically be
>>>> fine as that invokes is_skb_forwardable(), which we patch.
>>>>
>>> But there are other ways to forward packets, e.g tc-mirred or bpf
>>> redirect. We need to handle all these cases rather than fixing one at
>>> a time. As Jason suggested netif_needs_gso() looks like good function
>>> to validate if a device is capable of handling given GSO packet.
>>
>> I am not entirely sure this is a better solution.
>>
>> The biggest reason I am uncomfortable with this is that if
>> netif_needs_gso() returns true, the skb will be segmented. The segment
>> sizes will be based on gso_size. Since gso_size is greater than the MTU,
>> the resulting segments will themselves be over-MTU. Those over-MTU
>> segments will then be passed to the network card. I think we should not
>> be creating over-MTU segments; we should instead be dropping the packet
>> and logging.
>>
>
> Would this oversized segment cause the firmware assert?
> If this solves the assert issue then I do not see much value in adding
> checks in fast-path just for logging.
No - I tested this (or rather, as I don't have direct access to a bnx2x
card, this was tested on my behalf): as long as the packet is not a GSO
packet, it doesn't cause the crash. So we *could* segment them, I just
think that knowingly creating invalid segments is not particularly
pleasant.
Do you think my approach in a later email which checks and drops without
logging is sufficient? It is the same GSO check, and also checks non-GSO
packets against the MTU.
Regards,
Daniel
next prev parent reply other threads:[~2018-01-19 11:58 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-16 2:09 [PATCH 0/3] Check gso_size of packets when forwarding Daniel Axtens
2018-01-16 2:09 ` [PATCH 1/3] net: move skb_gso_mac_seglen to skbuff.h Daniel Axtens
2018-01-16 2:09 ` [PATCH 2/3] net: is_skb_forwardable: validate length of GSO packet segments Daniel Axtens
2018-01-18 23:47 ` Marcelo Ricardo Leitner
2018-01-16 2:09 ` [PATCH 3/3] openvswitch: drop GSO packets that are too large Daniel Axtens
[not found] ` <20180116020920.20232-1-dja-Yfaxwxk/+vWsTnJN9+BGXg@public.gmane.org>
2018-01-17 20:20 ` [PATCH 0/3] Check gso_size of packets when forwarding David Miller
2018-01-18 8:28 ` Pravin Shelar
2018-01-18 9:49 ` Jason Wang
2018-01-18 13:17 ` Daniel Axtens
[not found] ` <87fu735ms5.fsf-hbezLPf06/Fz8PszVLmxdVaj5H9X9Tb+@public.gmane.org>
2018-01-18 14:05 ` Daniel Axtens
[not found] ` <CAOrHB_AAMzYCLsFe6+3ODSqYUe79vYtP5jSxK=GDj5rKeQXyDA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-01-18 13:08 ` Daniel Axtens
2018-01-18 21:57 ` Pravin Shelar
[not found] ` <CAOrHB_CyTg4iZ38T0WeNkC6ng3iznXKk+0Qr-rA2rs7ivSSf+w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-01-19 1:28 ` Daniel Axtens
[not found] ` <87a7xa63ix.fsf-hbezLPf06/Fz8PszVLmxdVaj5H9X9Tb+@public.gmane.org>
2018-01-19 6:11 ` Daniel Axtens
2018-01-19 7:08 ` Pravin Shelar
2018-01-19 11:58 ` Daniel Axtens [this message]
[not found] ` <871sim5abx.fsf-hbezLPf06/Fz8PszVLmxdVaj5H9X9Tb+@public.gmane.org>
2018-01-19 21:54 ` Pravin Shelar
2018-01-22 20:14 ` David Miller
2018-01-22 21:31 ` Stephen Hemminger
2018-01-23 5:47 ` Pravin Shelar
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