netdev - Re: [PATCH 2/4] wan/hdlc

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Message-Id: <20190405.121529.675930084772235847.davem@davemloft.net>
Date:   Fri, 05 Apr 2019 12:15:29 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ms@....tdt.de
Cc:     andrew.hendry@...il.com, khc@...waw.pl, isdn@...ux-pingi.de,
        edumazet@...gle.com, linux-x25@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] wan/hdlc_x25: fix skb handling

From: Martin Schiller <ms@....tdt.de>
Date: Fri, 05 Apr 2019 08:56:44 +0200

> On 2019-04-05 02:32, David Miller wrote:
>> From: Martin Schiller <ms@....tdt.de>
>> Date: Wed,  3 Apr 2019 07:01:16 +0200
>> 
>>>  	/* X.25 to LAPB */
>>>  	switch (skb->data[0]) {
>>>  	case X25_IFACE_DATA:	/* Data to be transmitted */
>>> -		skb_pull(skb, 1);
>>> -		if ((result = lapb_data_request(dev, skb)) != LAPB_OK)
>>> -			dev_kfree_skb(skb);
>>> -		return NETDEV_TX_OK;
>>> +		skbn = skb_copy(skb, GFP_ATOMIC);
>>> +		skb_pull(skbn, 1);
>>> +		skb_reset_network_header(skbn);
>>> +		if ((result = lapb_data_request(dev, skbn)) != LAPB_OK)
>>> +			dev_kfree_skb(skbn);
>> This leaks 'skb'.
> 
> What exactly do you mean?
> 'skb' will get freed at the end of x25_xmit() function:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/wan/hdlc_x25.c#n129

Then why was it freed here in the original code?