netdev - Re: veth regression with "don’t modify ip_summed; doing so treats packets with bad checksums as good."

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]

Message-ID: <CAKUBDd-hw95+9EHiXj_4qhjK1iSvFpX4S2VOb+Cw5Z9of1b98g@mail.gmail.com>
Date:	Fri, 25 Mar 2016 17:51:16 -0400
From:	Vijay Pandurangan <vijayp@...ayp.ca>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	netdev <netdev@...r.kernel.org>, Evan Jones <ej@...njones.ca>,
	Cong Wang <cwang@...pensource.com>
Subject: Re: veth regression with "don’t modify ip_summed; doing so treats packets with bad checksums as good."

On Fri, Mar 25, 2016 at 10:35 AM, Ben Greear <greearb@...delatech.com> wrote:
>
>
> On 03/24/2016 10:24 PM, Vijay Pandurangan wrote:
>>
>> On Fri, Mar 25, 2016 at 1:07 AM, Ben Greear <greearb@...delatech.com>
>> wrote:
>>>
>>> On 03/24/2016 09:45 PM, Vijay Pandurangan wrote:
>>>>
>>>>
>>>> Actually, maybe they should be set to CHECKSUM_PARTIAL if we want veth
>>>> to drop the packets if they have bad checksums before they hit the
>>>> application level.
>>>
>>>
>>>
>>> VETH is pretty special in that when you transmit a frame on one
>>> device, it's pair receives it, and unless there is RAM corruption
>>> or bugs in the kernel, then it cannot be corrupted.
>>
>>
>> Yeah, you're right that that's an optimization. However, I think that
>> we should first ensure that
>>
>> a->veth->b
>>
>> operates exactly like:
>>
>> a->physical eth 1 -> physical eth 2->b
>>
>> in all cases.  Once we have that working everywhere we could think
>> about optimizations.
>>
>>
>> If we're willing to refactor, we could implement the optimization by
>> allowing veth devices to know whether their immediate peer is. If a
>> veth knows it's talking to another veth, it could under some
>> circumstances elide checksum calculation and verification.  I'm not
>> sure what abstractions that would break, though. What do you guys
>> think?
>
>
> veth ALWAYS transmits to another VETH.  The problem is that when veth is
> given a packet to transmit, it is difficult to know where that packet
> came from.

Yeah you're totally right – I guess what I was trying to express (but
failed at) was that we might need to be able to track the original
source of the packet for optimizations.
>
> And, adding software checksumming to veth for every frame would be a huge
> performance hit.
>
>
> Thanks,
> Ben
>
> --
> Ben Greear <greearb@...delatech.com>
> Candela Technologies Inc  http://www.candelatech.com