Re: [PATCH] can: j1939: j1939_sk_bind(): fix j1939_ecu leak when re-bind failed

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Netdevice refcount leak due to a race condition where the unregister notifier misses a socket during bind or re-bind list manipulations.
--

--- Patch [1]: [PATCH] can: j1939: j1939_sk_bind(): fix j1939_ecu leak when re-bind failed ---
commit 472bfe7c306ed38083d747b95430b318ca86c9cf
Author: Tetsuo Handa <[email protected]>

can: j1939: j1939_sk_bind(): fix j1939_ecu leak when re-bind failed

This commit fixes an ECU and net_device reference leak in j1939_sk_bind().
It defers removing the old ECU references during a re-bind operation until
after the new resources have been successfully acquired.

Closes: https://syzkaller.appspot.com/bug?extid=e2af46126e0644cbebdd

> diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
> index 50a598ef5fd4a..24efb25c58c3f 100644
> --- a/net/can/j1939/socket.c
> +++ b/net/can/j1939/socket.c

[ ... ]

> @@ -519,22 +517,31 @@ static int j1939_sk_bind(struct socket *sock, struct sockaddr_unsized *uaddr, in
>  		jsk->priv = priv;
>  	}
>  
> +	/* get new references without dropping old references */
> +	ret = j1939_local_ecu_get(priv, addr->can_addr.j1939.name, addr->can_addr.j1939.addr);
> +	if (ret) {
> +		/* nothing to undo if re-bind() failed */
> +		if (!was_bound) {
> +			j1939_netdev_stop(priv);
> +			jsk->priv = NULL;
> +			synchronize_rcu();
> +			j1939_priv_put(priv);
> +		}
> +		goto out_release_sock;
> +	}
> +
> +	/* drop old references after re-bind() succeeded */
> +	if (was_bound) {
> +		j1939_jsk_del(priv, jsk);

[Severity: High]
This isn't a bug introduced by this patch, but could this create a race
condition with netdevice unregistration during bind and re-bind?

When a socket takes a reference to priv during an initial bind (when
jsk->priv = priv is set), or during a re-bind when it is temporarily
removed from the list via j1939_jsk_del() right here, the socket is holding a
netdevice reference but is absent from the priv->j1939_socks list.

If j1939_sk_netdev_event_unregister() executes concurrently during this
window, it searches for sockets to clean up by iterating that exact list:

net/can/j1939/socket.c:j1939_sk_netdev_event_unregister() {
    ...
    list_for_each_entry(jsk, &priv->j1939_socks, list) {
        ...
    }
}

Could the unregister notifier miss the socket completely while it is
temporarily unlinked, skipping the mandatory cleanup and resulting in
unregister_netdevice() hanging indefinitely in netdev_wait_allrefs()?

> +		j1939_local_ecu_put(priv, jsk->addr.src_name, jsk->addr.sa);
> +	}
> +
>  	/* set default transmit pgn */
>  	if (j1939_pgn_is_valid(addr->can_addr.j1939.pgn))
>  		jsk->pgn_rx_filter = addr->can_addr.j1939.pgn;
>  	jsk->addr.src_name = addr->can_addr.j1939.name;
>  	jsk->addr.sa = addr->can_addr.j1939.addr;
>  
> -	/* get new references */
> -	ret = j1939_local_ecu_get(priv, jsk->addr.src_name, jsk->addr.sa);
> -	if (ret) {
> -		j1939_netdev_stop(priv);
> -		jsk->priv = NULL;
> -		synchronize_rcu();
> -		j1939_priv_put(priv);
> -		goto out_release_sock;
> -	}
> -
>  	j1939_jsk_add(priv, jsk);
>  
>   out_release_sock: /* fall through */

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1