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Date: Wed, 08 Oct 2003 09:09:48 -0400
From: Jeff Garzik <jgarzik@pobox.com>
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To: Tobias DiPasquale <toby@cbcg.net>
CC: netdev@oss.sgi.com, linux-net@vger.kernel.org,
       linux-kernel@vger.kernel.org, coreteam@netfilter.org,
       netfilter@lists.netfilter.org, akpm@zip.com.au, davem@redhat.com,
       kuznet@ms2.inr.ac.ru, pekkas@netcore.fi, jmorris@intercode.com.au,
       yoshfuji@linux-ipv6.org
Subject: Re: [PATCH] kfree_skb() bug in 2.4.22
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Tobias DiPasquale wrote:
> Hi all,
> 
> I was debugging one of my iptables/netfilter modules yesterday and I
> came across this bug in kfree_skb(). One of my functions returns a
> struct skbuff * on success and NULL on failure. When it failed, the code
> calling said function attempted to free the struct skbuff *, which at
> that point was NULL. This produced a kernel panic. I investigated the
> problem and found that, not only should I be checking for a NULL pointer
> when freeing the struct skbuff *, but the actual cause of the panic was
> because kfree_skb() and kfree_skb_fast() do not check for skb==NULL,
> either. They immediately attempt to dereference the users field of the
> struct skbuff * in order to decrement that reference counter. 


I would prefer that you fix your code instead, to not pass NULL to 
kfree_skb()...