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

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Message-ID: <CAHA+R7NvbJyjjBac=4VneQ_Nuxtb-_HEOJp0dujh5SOXj3NSKQ@mail.gmail.com>
Date:	Wed, 1 Apr 2015 17:06:54 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	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 Wed, Apr 1, 2015 at 8:07 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> From: "hannes@...essinduktion.org" <hannes@...essinduktion.org>
>
> We should not consult skb->sk for output decisions in xmit recursion
> levels > 0 in the stack. Otherwise local socket settings could influence
> the result of e.g. tunnel encapsulation process.
>
> ipv6 does not conform with this in three places:
>
> 1) ip6_fragment: we do consult ipv6_npinfo for frag_size
>
> 2) sk_mc_loop in ipv6 uses skb->sk and checks if we should
>    loop the packet back to the local socket
>
> 3) ip6_skb_dst_mtu could query the settings from the user socket and
>    force a wrong MTU
>
> Furthermore:
> In sk_mc_loop we could potentially land in WARN_ON(1) if we use a
> PF_PACKET socket ontop of an IPv6-backed vxlan device.
>
> Reuse xmit_recursion as we are currently only interested in protecting
> tunnel devices.
>

Shouldn't these skb's be orphaned for tunnel cases? Or we still have
to keep skb->sk for other valid use?
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