netdev - Re: race in skb_splice

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Message-Id: <200805282309.13628.opurdila@ixiacom.com>
Date:	Wed, 28 May 2008 23:09:13 +0300
From:	Octavian Purdila <opurdila@...acom.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Ben Hutchings <bhutchings@...arflare.com>,
	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: race in skb_splice_bits?

On Wednesday 28 May 2008, Jarek Poplawski wrote:

> >> We queue data under the lock and clone appropriate skb (and then grab it
> >> multiple times), so even it will be dropped, its data will not freed,
> >> and thus we will be able to read it. Or you are talking about different
> >> skbs?
> >
> > You are right, I forgot about the clone.
>
> Probably I miss something, but how does it help when tcp_collapse()
> uses __kfree_skb()?
>

__kfree_skb() -> skb_release_all() -> skb_release_data():

static void skb_release_data(struct sk_buff *skb)
{
        if (!skb->cloned ||
<snip>
                kfree(skb->head);

Since we clone the skb in skb_splice_bits() the skb's data will only be freed 
when the last clone is deleted.

tavi
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