netdev - Re: [PATCH net v3 2/2] mlx5: fix possible ptp queue fifo use-after-free

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Date:   Wed, 25 Jan 2023 17:09:05 -0800
From:   Rahul Rameshbabu <rrameshbabu@...dia.com>
To:     Vadim Fedorenko <vfedorenko@...ek.ru>
Cc:     Vadim Fedorenko <vadfed@...com>, Aya Levin <ayal@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Gal Pressman <gal@...dia.com>,
        Vadim Fedorenko <vadfed@...a.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net v3 2/2] mlx5: fix possible ptp queue fifo
 use-after-free

On Thu, 26 Jan, 2023 04:02:06 +0300 Vadim Fedorenko <vfedorenko@...ek.ru> wrote:
> From: Vadim Fedorenko <vadfed@...a.com>
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h b/drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h
> index 15a5a57b47b8..6e559b856afb 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h
> @@ -289,14 +289,19 @@ struct sk_buff **mlx5e_skb_fifo_get(struct mlx5e_skb_fifo *fifo, u16 i)
>  static inline
>  void mlx5e_skb_fifo_push(struct mlx5e_skb_fifo *fifo, struct sk_buff *skb)
>  {
> -	struct sk_buff **skb_item = mlx5e_skb_fifo_get(fifo, (*fifo->pc)++);
> +	struct sk_buff **skb_item;
>  
> +	WARN_ONCE(mlx5e_skb_fifo_has_room(fifo), "ptp fifo overflow");

I think you meant 'WARN_ONCE(!mlx5e_skb_fifo_has_room(fifo), "ptp fifo overflow");'?

It is only safe to push in the fifo when the fifo has room. Therefore,
we should warn when a push is attempted with no more room in the fifo.
Does this warning, as is, not trigger for you during testing in normal
conditions?

> +	skb_item = mlx5e_skb_fifo_get(fifo, (*fifo->pc)++);
>  	*skb_item = skb;
>  }