linux-kernel - Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation

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Message-ID: <CALYGNiOLhaY8mom01REK45O0fO=xLNgQUt4_tox9ymrqraNfAQ@mail.gmail.com>
Date:	Thu, 7 Jan 2016 15:04:14 +0300
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	Florian Westphal <fw@...len.de>,
	Thadeu Lima de Souza Cascardo <cascardo@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] skb corruption and kernel panic at forwarding with fragmentation

On Thu, Jan 7, 2016 at 2:59 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> On Thu, Jan 7, 2016 at 6:38 AM, Konstantin Khlebnikov <koct9i@...il.com> wrote:
>>
>> Also I've found strange thing: reason of expanding skb->cb from 40 to
>> 48 bypes in 2006
>> 3e3850e989c5d2eb1aab6f0fd9257759f0f4cbc6 was that struct inet6_skb_parm does
>> not fit. But it's is only 24 bytes. Does some arches add pad after
>> each _u16 field?
>
> "struct inet6_skb_parm" is part of struct tcp_skb_cb
>
> This is why Patrick had to increase skb->cb[]

Whoa. Funny. TCP moves that chunk back and forward instead of just
putting it at the first place in struct.
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