linux-kernel - Re: [PATCH] veth: don't modify ip-summed; doing so treats packets with bad checksums as good.

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Message-ID: <CAM_iQpVAZ=C68f1BGNEV=e-WGaJrvR-pzu_6kqCGnJLo8gw6Pg@mail.gmail.com>
Date:	Sat, 19 Dec 2015 13:01:27 -0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Vijay Pandurangan <vijayp@...ayp.ca>
Cc:	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Phil Sutter <phil@....cc>,
	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Evan Jones <ej@...njones.ca>,
	Eric Biederman <ebiederm@...stanetworks.com>,
	Tom Herbert <tom@...bertland.com>
Subject: Re: [PATCH] veth: don't modify ip-summed; doing so treats packets
 with bad checksums as good.

On Fri, Dec 18, 2015 at 11:42 AM, Vijay Pandurangan <vijayp@...ayp.ca> wrote:
> Evan and I have demonstrated this bug on Kubernetes as well, so it's
> not just a problem in Mesos. (See
> https://github.com/kubernetes/kubernetes/issues/18898)
>

Interesting... then this problem is much more serious than I thought.

Looks like in RX path the bridge sets the checksum to CHECKSUM_NONE
too:

static inline void skb_forward_csum(struct sk_buff *skb)
{
        /* Unfortunately we don't support this one.  Any brave souls? */
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->ip_summed = CHECKSUM_NONE;
}

I guess this is probably why Docker/Kubernetes could be affected too.
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