netdev - Re: [PATCH v3] net: af_packet: don't call tpacket_destruct

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Message-ID: <1285252912.2509.29.camel@edumazet-laptop>
Date:	Thu, 23 Sep 2010 16:41:52 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	"Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v3] net: af_packet: don't call tpacket_destruct_skb()
 until the skb is sent out

Le jeudi 23 septembre 2010 à 22:17 +0800, Changli Gao a écrit :
> On Thu, Sep 23, 2010 at 8:29 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Le jeudi 23 septembre 2010 à 18:15 +0800, Changli Gao a écrit :
> >> Since skb->destructor() is used to account socket memory, and maybe called
> >> before the skb is sent out, a corrupt skb maybe sent out finally.
> >>
> >> A new destructor is added into structure skb_shared_info(), and it won't
> >> be called until the last reference to the data of an skb is put. af_packet
> >> uses this destructor instead.
> >>
> >> Signed-off-by: Changli Gao <xiaosuo@...il.com>
> >> ---
> >> v3: rename destructor to data_destructor, destructor_arg to data_destructor_arg,
> >>     fix splice the skbs generated by AF_PACKET socket to the pipe.
> >
> > I dont understand this.
> >
> > Could you describe how splice(from af_packet to pipe) is possible with
> > af_packet send path ?
> 
> af_packet sends packets to lo(127.0.0.1), and a local socket is
> receiving packets via splice.

Ouch

I am pretty sure too many things will break if we allow such packets to
get back in input path.

(think of tcp coalescing for example...)



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