Subject: Re: [PATCH net] net: hsr: prevent NULL pointer dereference in hsr_proxy_announce()

From: Lukasz Majewski <[email-masked]>
Date: Mon, 9 Sep 2024 10:58:22 +0200

Hi Jeongjun,

> In the function hsr_proxy_annouance() added in the previous commit 
> 5f703ce5c981 ("net: hsr: Send supervisory frames to HSR network 
> with ProxyNodeTable data"), the return value of the
> hsr_port_get_hsr() function is not checked to be a NULL pointer,
> which causes a NULL pointer dereference.

Thank you for your patch.

The code in hsr_proxy_announcement() is _only_ executed (the timer is
configured to trigger this function) when hsr->redbox is set, which
means that somebody has called earlier iproute2 command:

ip link add name hsr1 type hsr slave1 lan4 slave2 lan5 interlink lan3
supervision 45 version 1

> 
> To solve this, we need to add code to check whether the return value 
> of hsr_port_get_hsr() is NULL.
> 
> Reported-by: [email-masked]
> Fixes: 5f703ce5c981 ("net: hsr: Send supervisory frames to HSR
> network with ProxyNodeTable data") Signed-off-by: Jeongjun Park
> <[email-masked]> ---
>  net/hsr/hsr_device.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
> index e4cc6b78dcfc..b3191968e53a 100644
> --- a/net/hsr/hsr_device.c
> +++ b/net/hsr/hsr_device.c
> @@ -427,6 +427,9 @@ static void hsr_proxy_announce(struct timer_list
> *t)
>  	 * of SAN nodes stored in ProxyNodeTable.
>  	 */
>  	interlink = hsr_port_get_hsr(hsr, HSR_PT_INTERLINK);
> +	if (!interlink)
> +		goto done;
> +
>  	list_for_each_entry_rcu(node, &hsr->proxy_node_db, mac_list)
> { if (hsr_addr_is_redbox(hsr, node->macaddress_A))
>  			continue;
> @@ -441,6 +444,7 @@ static void hsr_proxy_announce(struct timer_list
> *t) mod_timer(&hsr->announce_proxy_timer, jiffies + interval);
>  	}
>  
> +done:
>  	rcu_read_unlock();
>  }
>  
> --

Best regards,

Lukasz Majewski

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