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

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Date:	Mon, 27 Sep 2010 05:46:57 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	xiaohui.xin@...el.com, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	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

On Mon, Sep 27, 2010 at 09:24:02AM +0800, Changli Gao wrote:
> On Fri, Sep 24, 2010 at 2:36 PM, Jarek Poplawski <jarkao2@...il.com> wrote:
> > On 2010-09-23 12:15, Changli Gao wrote:
> >> 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.
> >
> > IMHO, we shouldn't allow for fixing the bad design of one protocol at
> > the expense of others by adding more and more conditionals. The proper
> > way of handling paged skbs (splice compatible) exists. And the current
> > patch doesn't even fix the problem completely against things like
> > pskb_expand_head or pskb_copy.
> 
> pskb_expand_head is handled in my patch, but not pskb_copy().

It's not enough: "skb_shinfo(skb)->data_destructor = NULL" means
skb_release_data() for the original skb->data will not have one, and
you don't know which of the two releases will be the last.

Jarek P.
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