netdev - Re: [PATCH net] can: j1939: fix UAF for rx_kref of j1939

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Date:   Fri, 8 Oct 2021 13:34:15 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Ziyang Xuan <william.xuanziyang@...wei.com>
Cc:     robin@...tonic.nl, linux@...pel-privat.de, socketcan@...tkopp.net,
        mkl@...gutronix.de, davem@...emloft.net, kuba@...nel.org,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] can: j1939: fix UAF for rx_kref of j1939_priv

Hi,

On Sun, Sep 26, 2021 at 06:47:57PM +0800, Ziyang Xuan wrote:
> It will trigger UAF for rx_kref of j1939_priv as following.
> 
>         cpu0                                    cpu1
> j1939_sk_bind(socket0, ndev0, ...)
> j1939_netdev_start
>                                         j1939_sk_bind(socket1, ndev0, ...)
>                                         j1939_netdev_start
> j1939_priv_set
>                                         j1939_priv_get_by_ndev_locked
> j1939_jsk_add
> .....
> j1939_netdev_stop
> kref_put_lock(&priv->rx_kref, ...)
>                                         kref_get(&priv->rx_kref, ...)
>                                         REFCOUNT_WARN("addition on 0;...")
> 
> ====================================================
> refcount_t: addition on 0; use-after-free.
> WARNING: CPU: 1 PID: 20874 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0
> RIP: 0010:refcount_warn_saturate+0x169/0x1e0
> Call Trace:
>  j1939_netdev_start+0x68b/0x920
>  j1939_sk_bind+0x426/0xeb0
>  ? security_socket_bind+0x83/0xb0
> 
> The rx_kref's kref_get() and kref_put() should use j1939_netdev_lock to
> protect.
> 
> Fixes: 9d71dd0c70099 ("can: add support of SAE J1939 protocol")
> Reported-by: syzbot+85d9878b19c94f9019ad@...kaller.appspotmail.com
> Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com>

Thank you!

Acked-by: Oleksij Rempel <o.rempel@...gutronix.de>

> ---
>  net/can/j1939/main.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/can/j1939/main.c b/net/can/j1939/main.c
> index 08c8606cfd9c..9bc55ecb37f9 100644
> --- a/net/can/j1939/main.c
> +++ b/net/can/j1939/main.c
> @@ -249,11 +249,14 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev)
>  	struct j1939_priv *priv, *priv_new;
>  	int ret;
>  
> -	priv = j1939_priv_get_by_ndev(ndev);
> +	spin_lock(&j1939_netdev_lock);
> +	priv = j1939_priv_get_by_ndev_locked(ndev);
>  	if (priv) {
>  		kref_get(&priv->rx_kref);
> +		spin_unlock(&j1939_netdev_lock);
>  		return priv;
>  	}
> +	spin_unlock(&j1939_netdev_lock);
>  
>  	priv = j1939_priv_create(ndev);
>  	if (!priv)
> @@ -269,10 +272,10 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev)
>  		/* Someone was faster than us, use their priv and roll
>  		 * back our's.
>  		 */
> +		kref_get(&priv_new->rx_kref);
>  		spin_unlock(&j1939_netdev_lock);
>  		dev_put(ndev);
>  		kfree(priv);
> -		kref_get(&priv_new->rx_kref);
>  		return priv_new;
>  	}
>  	j1939_priv_set(ndev, priv);
> -- 
> 2.25.1
> 
> 

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