linux-kernel - Re: [PATCH 1/2] net/x25: Fix x25_neigh refcnt leak when x25

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Date:   Thu, 23 Apr 2020 09:00:42 +0200
From:   Martin Schiller <ms@....tdt.de>
To:     Xiyu Yang <xiyuyang19@...an.edu.cn>
Cc:     Andrew Hendry <andrew.hendry@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-x25@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, yuanxzhang@...an.edu.cn,
        kjlu@....edu, Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH 1/2] net/x25: Fix x25_neigh refcnt leak when x25_connect()
 fails

On 2020-04-23 07:13, Xiyu Yang wrote:
> x25_connect() invokes x25_get_neigh(), which returns a reference of the
> specified x25_neigh object to "x25->neighbour" with increased refcnt.
> 
> When x25_connect() returns, local variable "x25" and "x25->neighbour"
> become invalid, so the refcount should be decreased to keep refcount
> balanced.
> 
> The reference counting issue happens in one exception handling path of
> x25_connect(). When sock state is not TCP_ESTABLISHED and its flags
> include O_NONBLOCK, the function forgets to decrease the refcnt
> increased by x25_get_neigh(), causing a refcnt leak.
> 
> Fix this issue by jumping to "out_put_neigh" label when x25_connect()
> fails.

I don't agree with that.
Please have a look at commit e21dba7a4df4 ("net/x25: fix nonblocking 
connect).

But I also think you are right and there seems to be a refcnt leak,
which should be fixed by a call to x25_neigh_put() in the
x25_disconnect() function.

- Martin


> 
> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
> ---
>  net/x25/af_x25.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
> index d5b09bbff375..e6571c56209b 100644
> --- a/net/x25/af_x25.c
> +++ b/net/x25/af_x25.c
> @@ -816,7 +816,7 @@ static int x25_connect(struct socket *sock, struct
> sockaddr *uaddr,
>  	/* Now the loop */
>  	rc = -EINPROGRESS;
>  	if (sk->sk_state != TCP_ESTABLISHED && (flags & O_NONBLOCK))
> -		goto out;
> +		goto out_put_neigh;
> 
>  	rc = x25_wait_for_connection_establishment(sk);
>  	if (rc)