netdev - Re: ipv6: handle -EFAULT from skb_copy

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Message-Id: <20161220.132813.435056880928769245.davem@davemloft.net>
Date:   Tue, 20 Dec 2016 13:28:13 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     davej@...emonkey.org.uk
Cc:     netdev@...r.kernel.org
Subject: Re: ipv6: handle -EFAULT from skb_copy_bits

From: Dave Jones <davej@...emonkey.org.uk>
Date: Tue, 20 Dec 2016 13:17:28 -0500

> 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
> 
> Shouldn't we have kicked out data_len=0 skb's somewhere before we got this far ?

skb->data_len is just the length of any non-linear data in the SKB.

This has to do with the SKB buffer layout and geometry, not whether
the packet is "fragmented" in the protocol sense.

So no, this isn't a criteria for packets being filtered out by this
point.

Can you try to capture what sk->sk_socket->type and
inet_sk(sk)->hdrincl are set to at the time of the crash?

Thanks.