Subject: Re: [PATCH v1 iwl-net] iavf: fix out-of-bounds writes in iavf_get_ethtool_stats()

From: Simon Horman <[email-masked]>
Date: Mon, 16 Feb 2026 13:19:09 +0000

On Sat, Feb 14, 2026 at 07:14:25PM +0000, Kohei Enju wrote:
> iavf incorrectly uses real_num_tx_queues for ETH_SS_STATS. Since the
> value could change in runtime, we should use num_tx_queues instead.
> 
> Moreover iavf_get_ethtool_stats() uses num_active_queues while
> iavf_get_sset_count() and iavf_get_stat_strings() use
> real_num_tx_queues, which triggers out-of-bounds writes when we do
> "ethtool -L" and "ethtool -S" simultaneously [1].
> 
> For example when we change channels from 1 to 8, Thread 3 could be
> scheduled before Thread 2, and out-of-bounds writes could be triggered
> in Thread 3:
> 
> Thread 1 (ethtool -L)       Thread 2 (work)        Thread 3 (ethtool -S)
> iavf_set_channels()
> ...
> iavf_alloc_queues()
> -> num_active_queues = 8
> iavf_schedule_finish_config()
>                                                    iavf_get_sset_count()
>                                                    real_num_tx_queues: 1
>                                                    -> buffer for 1 queue
>                                                    iavf_get_ethtool_stats()
>                                                    num_active_queues: 8
>                                                    -> out-of-bounds!
>                             iavf_finish_config()
>                             -> real_num_tx_queues = 8

...

> Fixes: 64430f70ba6f ("iavf: Fix displaying queue statistics shown by ethtool")
> Signed-off-by: Kohei Enju <[email-masked]>

...

> @@ -345,19 +344,19 @@ static void iavf_get_ethtool_stats(struct net_device *netdev,
>  	iavf_add_ethtool_stats(&data, adapter, iavf_gstrings_stats);
>  
>  	rcu_read_lock();
> -	/* As num_active_queues describe both tx and rx queues, we can use
> -	 * it to iterate over rings' stats.
> +	/* Use num_tx_queues to report stats for the maximum number of queues.
> +	 * Queues beyond num_active_queues will report zero.
>  	 */
> -	for (i = 0; i < adapter->num_active_queues; i++) {
> -		struct iavf_ring *ring;
> +	for (i = 0; i < netdev->num_tx_queues; i++) {
> +		struct iavf_ring *tx_ring = NULL, *rx_ring = NULL;
>  
> -		/* Tx rings stats */
> -		ring = &adapter->tx_rings[i];
> -		iavf_add_queue_stats(&data, ring);
> +		if (i < adapter->num_active_queues) {

Hi Enju-san,

If I understand things correctly, in the scenario described in the patch
description, num_active_queues will be 8 here.

Won't that result in an overflow?

> +			tx_ring = &adapter->tx_rings[i];
> +			rx_ring = &adapter->rx_rings[i];
> +		}
>  
> -		/* Rx rings stats */
> -		ring = &adapter->rx_rings[i];
> -		iavf_add_queue_stats(&data, ring);
> +		iavf_add_queue_stats(&data, tx_ring);
> +		iavf_add_queue_stats(&data, rx_ring);
>  	}
>  	rcu_read_unlock();
>  }

...