netdev - Re: [net] net: fix double free issue of skbuff

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Message-Id: <20160229.121153.1765066549122216101.davem@davemloft.net>
Date:	Mon, 29 Feb 2016 12:11:53 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	zhangshengju@...s.chinamobile.com
Cc:	pabeni@...hat.com, netdev@...r.kernel.org
Subject: Re: [net] net: fix double free issue of skbuff

From: 张胜举 <zhangshengju@...s.chinamobile.com>
Date: Mon, 29 Feb 2016 22:16:37 +0800

>> On Mon, 2016-02-29 at 12:22 +0000, Zhang Shengju wrote:
>> > If skb_reorder_vlan_header() failed, skb is freed and NULL is returned.
>> > Then at skb_vlan_untag(), it will free skbuff again which cause double
>> > free.
>> 
>> On skb_reorder_vlan_header() failure, skb_vlan_untag() will call
>> kfree_skb() using the return value of skb_reorder_vlan_header(), that is
>> NULL. kfree_skb() is a noop when the argument is NULL.
>> 
>> The current code seams safe.
>> 
>> Paolo
> Hi Paolo, even current code is safe, this's still a potential problem. We should make an
> assumption that inner function doesn't free skb, and let outside function take care of this.

No, the current code is intentional and perfectly fine.

Fix real bugs, not imaginary ones.

Thanks.