netdev - Re: [PATCH net 2/2] netdev: Enforce index cap in netdev_get_tx

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Date:   Fri, 17 Mar 2023 19:45:14 +0100
From:   Piotr Raczynski <piotr.raczynski@...el.com>
To:     Nick Child <nnac123@...ux.ibm.com>
CC:     <netdev@...r.kernel.org>
Subject: Re: [PATCH net 2/2] netdev: Enforce index cap in netdev_get_tx_queue

On Fri, Mar 17, 2023 at 01:19:41PM -0500, Nick Child wrote:
> When requesting a TX queue at a given index, prevent out-of-bounds
> referencing by ensuring that the index is within the allocated number
> of queues.
> 
> If there is an out-of-bounds reference then inform the user and return
> a reference to the first tx queue instead.
> 
> Fixes: e8a0464cc950 ("netdev: Allocate multiple queues for TX.")
> Signed-off-by: Nick Child <nnac123@...ux.ibm.com>
> ---
>  include/linux/netdevice.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 23b0d7eaaadd..fe88b1a7393d 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2482,6 +2482,13 @@ static inline
>  struct netdev_queue *netdev_get_tx_queue(const struct net_device *dev,
>  					 unsigned int index)
>  {
> +	if (unlikely(index >= dev->num_tx_queues)) {
> +		net_warn_ratelimited("%s selects TX queue %d, but number of TX queues is %d\n",
> +				     dev->name, index,
> +				     dev->num_tx_queues);
> +		return &dev->_tx[0];

Why return first queue here instead of NULL, wouldn't that confuse the
caller instead of return proper (NULL) value?

Piotr.
> +	}
> +
>  	return &dev->_tx[index];
>  }
>  
> -- 
> 2.31.1
>