netdev - Re: [PATCH net-next] ipv6: protect skb->sk accesses from recursive dereference inside the stack

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Date:	Wed, 01 Apr 2015 18:53:50 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Cong Wang <cwang@...pensource.com>,
	netdev <netdev@...r.kernel.org>, Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH net-next] ipv6: protect skb->sk accesses from recursive
 dereference inside the stack

On Thu, 2015-04-02 at 02:56 +0200, Hannes Frederic Sowa wrote:
> 
> On Thu, Apr 2, 2015, at 02:48, Eric Dumazet wrote:
> > On Thu, 2015-04-02 at 02:35 +0200, Hannes Frederic Sowa wrote:
> > > On Thu, Apr 2, 2015, at 02:27, Eric Dumazet wrote: 
> > > > orphaning skb just because they traverse a tunnel would be quite
> > > > horrible.
> > > 
> > > Agreed, but we have some bits in the skb->sk pointer left for signaling
> > > we are only keeping it around for destructor and upper layer
> > > notifications. Destructors should be the only ones having to deal with
> > > skb->sk and they can mask the bit. That would touch a lot of NULL
> > > checks, though.
> > 
> > Have you checked net/sched/sch_fq.c per chance ?
> > 
> > skb->sk is not an opaque value.
> 
> Do you think that skb->sk access through skb->__sk & ~0x1ULL would slow
> down the code too much?

I was only replying to your claim "Destructors should be the only ones
having to deal with skb->sk", which looked wrong to me.

Adding bit masking would slow down the code, but we did this already for
skb->dst



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