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Date:   Fri, 21 Jan 2022 22:36:45 +0300
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Subject: Re: [PATCH] drivers: net: remove a dangling pointer in
 peak_usb_create_dev
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To:     Dongliang Mu <mudongliangabcd@gmail.com>
Cc:     Dongliang Mu <dzm91@hust.edu.cn>,
        Wolfgang Grandegger <wg@grandegger.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Stephane Grosjean <s.grosjean@peak-system.com>,
        =?UTF-8?Q?Stefan_M=c3=a4tje?= <stefan.maetje@esd.eu>,
        Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
        linux-can@vger.kernel.org,
        "open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <20220120130605.55741-1-dzm91@hust.edu.cn>
 <b5cb1132-2f6b-e2da-78c7-1828b3617bc3@gmail.com>
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 <CAD-N9QUZ95zqboe=58gybue6ssSO-M-raijd3XnGXkXnp3wiqQ@mail.gmail.com>
From:   Pavel Skripkin <paskripkin@gmail.com>
In-Reply-To: <CAD-N9QUZ95zqboe=58gybue6ssSO-M-raijd3XnGXkXnp3wiqQ@mail.gmail.com>
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Hi Dongliang,

On 1/21/22 08:58, Dongliang Mu wrote:
[...]>> BTW, as you mentioned, dev->next_siblings is used in struct
>> peak_usb_adapter::dev_free() (i.e., pcan_usb_fd_free or
>> pcan_usb_pro_free), how about the following path?
>>
>> peak_usb_probe
>> -> peak_usb_create_dev (goto adap_dev_free;)
>>    -> dev->adapter->dev_free()
>>       -> pcan_usb_fd_free or pcan_usb_pro_free (This function uses
>> next_siblings as condition elements)
>>
>> static void pcan_usb_fd_free(struct peak_usb_device *dev)
>> {
>>         /* last device: can free shared objects now */
>>         if (!dev->prev_siblings && !dev->next_siblings) {
>>                 struct pcan_usb_fd_device *pdev =
>>                         container_of(dev, struct pcan_usb_fd_device, dev);
>>
>>                 /* free commands buffer */
>>                 kfree(pdev->cmd_buffer_addr);
>>
>>                 /* free usb interface object */
>>                 kfree(pdev->usb_if);
>>         }
>> }
>>
>> If next_siblings is not NULL, will it lead to the missing free of
>> cmd_buffer_addr and usb_if?
> 
> The answer is No. Forget my silly thought.
> 

Yeah, it seems like (at least based on code), that this dangling pointer 
is not dangerous, since nothing accesses it. And next_siblings 
_guaranteed_ to be NULL, since dev->next_siblings is set NULL in 
disconnect()


With regards,
Pavel Skripkin