Re: ipv6: handle -EFAULT from skb_copy_bits

From: Dave Jones <redacted>
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 [off-list ref]
 > 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.