netdev - Re: [PATCH net-next v3 2/8] gtp: switch from struct socket to struct sock for the GTP sockets

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Date:   Wed, 15 Feb 2017 08:04:56 +0100 (CET)
From:   Andreas Schultz <aschultz@...p.net>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     pablo <pablo@...filter.org>, netdev <netdev@...r.kernel.org>,
        laforge <laforge@...monks.org>,
        Lionel Gauthier <Lionel.Gauthier@...ecom.fr>,
        osmocom-net-gprs@...ts.osmocom.org, Jonas Bonn <jonas@...thpole.se>
Subject: Re: [PATCH net-next v3 2/8] gtp: switch from struct socket to
 struct sock for the GTP sockets

----- On Feb 14, 2017, at 6:48 PM, David S. Miller davem@...emloft.net wrote:

> From: Andreas Schultz <aschultz@...p.net>
> Date: Mon, 13 Feb 2017 16:36:18 +0100
> 
>> +	if (gtp->sk0) {
>> +		udp_sk(gtp->sk0)->encap_type = 0;
>> +		rcu_assign_sk_user_data(gtp->sk0, NULL);
>> +		sock_put(gtp->sk0);
>>  	}
> 
> This does "sock_put(NULL);" because you are assigning gtp->sk0 to
> NULL before the sock_put() call.  So you are leaking the socket,
> at best.

I don't understand how this should happen. If I where to use rcu_assign_pointer,
then yes, but rcu_assign_sk_user_data does assign to the sk_user_data member
of struct sock and not to the argument itself.

Andreas