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

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Message-ID: <1427935725.25985.179.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 01 Apr 2015 17:48:45 -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 02:35 +0200, Hannes Frederic Sowa wrote:
> 
> On Thu, Apr 2, 2015, at 02:27, Eric Dumazet wrote:
> > On Wed, 2015-04-01 at 17:06 -0700, Cong Wang wrote:
> > 
> > > Shouldn't these skb's be orphaned for tunnel cases? Or we still have
> > > to keep skb->sk for other valid use?
> > 
> > skb should not be orphaned, until the very last stage.
> > 
> > Many layers depend on this, really.
> > 
> > Simply ask the question to yourself :
> > 
> > What if I do not associate skb to a socket at first. What possibly
> > breaks ?
> > 
> > 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.


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