Subject: Re: [PATCH 1/2] net/x25: Fix x25_neigh refcnt leak when x25_connect() fails

From: Martin Schiller <[email-masked]>
Date: Thu, 23 Apr 2020 09:00:42 +0200

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 <[email-masked]>
> Signed-off-by: Xin Tan <[email-masked]>
> ---
>  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)