netdev - Re: [PATCH net] can: raw: fix receiver memory leak

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Date: Fri, 7 Jul 2023 09:59:00 +0800
From: "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>
To: Oliver Hartkopp <socketcan@...tkopp.net>, <mkl@...gutronix.de>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <linux-can@...r.kernel.org>, <netdev@...r.kernel.org>,
	<penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH net] can: raw: fix receiver memory leak

> On 06.07.23 14:48, Ziyang Xuan (William) wrote:
> 
> (..)
> 
>>>>        }
>>>>       out:
>>>>        release_sock(sk);
>>>> +    rtnl_unlock();
>>>
>>> Would it also fix the issue when just adding the rtnl_locks to raw_bind() and raw_release() as suggested by you?
>>
>> This patch just add rtnl_lock in raw_bind() and raw_release(). raw_setsockopt() has rtnl_lock before this. raw_notify()
>> is under rtnl_lock. My patch has been tested and solved the issue before send. I don't know if it answered your doubts.
> 
> My question was whether adding rtnl_locks to raw_bind() and raw_release() would be enough to fix the issue.
> 
> Without introducing the additional ro->dev element!?

Understand. Just add rtnl_lock to raw_bind() and raw_release() can not fix the issue. I tested.

We should understand that unregister a net device is divided into two stages generally.
Fistly, call unregister_netdevice_many() to remove net_dev from device list and add
net_dev to net_todo_list. Secondly, free net_dev in netdev_run_todo().

In my issue. Firstly, unregister_netdevice_many() removed can_dev from device
list and added can_dev to net_todo_list. Then got NULL by dev_get_by_index()
and receivers in dev_rcv_lists would not be freed in raw_release().
After raw_release(), ro->bound would be set 0. When NETDEV_UNREGISTER event
arrived raw_notify(), receivers in dev_rcv_lists would not be freed too
because ro->bound was already 0. Thus receivers in dev_rcv_lists would be leaked.

             cpu0                                        cpu1
unregister_netdevice_many(can_dev)
  unlist_netdevice(can_dev) // dev_get_by_index() return NULL after this
  net_set_todo(can_dev)
						raw_release(can_socket)
						  dev = dev_get_by_index(, ro->ifindex); // dev == NULL
						  if (dev) { // receivers in dev_rcv_lists not free because dev is NULL
						    raw_disable_allfilters(, dev, );
						    dev_put(dev);
						  }
						...
						ro->bound = 0;
						...

netdev_wait_allrefs_any()
  call_netdevice_notifiers(NETDEV_UNREGISTER, )
    raw_notify(, NETDEV_UNREGISTER, )
      if (ro->bound) // invalid because ro->bound has been set 0
        raw_disable_allfilters(, dev, ); // receivers in dev_rcv_lists will never be freed


Thanks,
William Xuan

> 
> Best regards,
> Oliver
> .