netdev - Re: ipv6: handle -EFAULT from skb_copy

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Date:   Tue, 20 Dec 2016 11:31:38 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Dave Jones <davej@...emonkey.org.uk>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: ipv6: handle -EFAULT from skb_copy_bits

On Tue, Dec 20, 2016 at 10:17 AM, Dave Jones <davej@...emonkey.org.uk> wrote:
> On Mon, Dec 19, 2016 at 08:36:23PM -0500, David Miller wrote:
>  > From: Dave Jones <davej@...emonkey.org.uk>
>  > Date: Mon, 19 Dec 2016 19:40:13 -0500
>  >
>  > > On Mon, Dec 19, 2016 at 07:31:44PM -0500, Dave Jones wrote:
>  > >
>  > >  > Unfortunately, this made no difference.  I spent some time today trying
>  > >  > to make a better reproducer, but failed. I'll revisit again tomorrow.
>  > >  >
>  > >  > Maybe I need >1 process/thread to trigger this.  That would explain why
>  > >  > I can trigger it with Trinity.
>  > >
>  > > scratch that last part, I finally just repro'd it with a single process.
>  >
>  > Thanks for the info, I'll try to think about this some more.
>
> I threw in some debug printks right before that BUG_ON.
> it's always this:
>
> skb->len=31 skb->data_len=0 offset:30 total_len:9

Clearly we fail because 30 > 31 - 2, seems 'offset' is not correct here,
off-by-one?