Subject: Re: [PATCH net] tuntap: correctly wake up process during uninit

From: Jason Wang <[email-masked]>
Date: Thu, 19 May 2016 13:35:03 +0800

On 2016年05月18日 21:01, Eric Dumazet wrote:
> On Wed, 2016-05-18 at 18:58 +0800, Jason Wang wrote:
>> We used to check dev->reg_state against NETREG_REGISTERED after each
>> time we are woke up. But after commit 9e641bdcfa4e ("net-tun:
>> restructure tun_do_read for better sleep/wakeup efficiency"), it uses
>> skb_recv_datagram() which does not check dev->reg_state. This will
>> result if we delete a tun/tap device after a process is blocked in the
>> reading. The device will wait for the reference count which was held
>> by that process for ever.
>>
>> Fixes this by using RCV_SHUTDOWN which will be checked during
>> sk_recv_datagram() before trying to wake up the process during uninit.
>>
>> Fixes: 9e641bdcfa4e ("net-tun: restructure tun_do_read for better
>> sleep/wakeup efficiency")
> <nit : no newline before Fixes: and other parts>

Ok.

> Cc: Eric Dumazet <[email-masked]>
> Cc: Xi Wang <[email-masked]>
> Cc: Michael S. Tsirkin <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>
> ---
> The patch is needed for -stable.
> ---
>   drivers/net/tun.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 425e983..752d849 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -580,11 +580,13 @@ static void tun_detach_all(struct net_device *dev)
>   	for (i = 0; i < n; i++) {
>   		tfile = rtnl_dereference(tun->tfiles[i]);
>   		BUG_ON(!tfile);
> +		tfile->socket.sk->sk_shutdown = RCV_SHUTDOWN;
>   		tfile->socket.sk->sk_data_ready(tfile->socket.sk);
>   		RCU_INIT_POINTER(tfile->tun, NULL);
>   		--tun->numqueues;
>   	}
>   	list_for_each_entry(tfile, &tun->disabled, next) {
> +		tfile->socket.sk->sk_shutdown = RCV_SHUTDOWN;
>   		tfile->socket.sk->sk_data_ready(tfile->socket.sk);
>   		RCU_INIT_POINTER(tfile->tun, NULL);
>   	}
> @@ -641,6 +643,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file, bool skip_filte
>   			goto out;
>   	}
>   	tfile->queue_index = tun->numqueues;
> +	tfile->socket.sk->sk_shutdown &= ~RCV_SHUTDOWN;
>   	rcu_assign_pointer(tfile->tun, tun);
>   	rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
>   	tun->numqueues++;
> Is the "if (tun->dev->reg_state != NETREG_REGISTERED) return -EIO;"
> check still needed then ?
>
> Thanks.
>
>

No need since we've check tun before, will remove this in V2.

Thanks