netdev - Re: [PATCH] net: mlx5: fix a potential NULL pointer dereference

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Date:   Mon, 11 Mar 2019 18:46:31 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "kjlu@....edu" <kjlu@....edu>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "pakki001@....edu" <pakki001@....edu>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "leon@...nel.org" <leon@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: mlx5: fix a potential NULL pointer dereference

On Mon, 2019-03-11 at 01:33 -0500, Kangjie Lu wrote:
> In case skb_header_pointer fails, the fix issues a warning.
> 

This case is impossible: mlx5 driver builds this skb itself so we are
sure skb_header_pointer never fails.

What is the motivation behind this fix? static checker or actual issue
?

> A better fix requires modifying the signature of mlx5e_get_fcs to
> pass an error code upstream.
> 
> Signed-off-by: Kangjie Lu <kjlu@....edu>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> index be396e5e4e39..6ec1c110e4be 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> @@ -719,6 +719,8 @@ static u32 mlx5e_get_fcs(const struct sk_buff
> *skb)
>  
>  	fcs_bytes = skb_header_pointer(skb, skb->len - ETH_FCS_LEN,
>  				       ETH_FCS_LEN, &_fcs_bytes);
> +	if (unlikely(!fcs_bytes))
> +		pr_warn_once("skb_header_pointer returns NULL\n");
>  
>  	return __get_unaligned_cpu32(fcs_bytes);
>  }