linux-kernel - Re: [PATCH] igb: Add MII write support

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Date: Wed, 5 Jun 2024 13:51:24 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: <jackie.jone@...iedtelesis.co.nz>, <davem@...emloft.net>
CC: <jesse.brandeburg@...el.com>, <anthony.l.nguyen@...el.com>,
	<kuba@...nel.org>, <intel-wired-lan@...ts.osuosl.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<chris.packham@...iedtelesis.co.nz>
Subject: Re: [PATCH] igb: Add MII write support



On 6/3/2024 8:10 PM, jackie.jone@...iedtelesis.co.nz wrote:
> From: Jackie Jone <jackie.jone@...iedtelesis.co.nz>
> 
> To facilitate running PHY parametric tests, add support for the SIOCSMIIREG
> ioctl. This allows a userspace application to write to the PHY registers
> to enable the test modes.
> 
> Signed-off-by: Jackie Jone <jackie.jone@...iedtelesis.co.nz>
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> index 03a4da6a1447..7fbfcf01fbf9 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -8977,6 +8977,10 @@ static int igb_mii_ioctl(struct net_device *netdev, struct ifreq *ifr, int cmd)
>  			return -EIO;
>  		break;
>  	case SIOCSMIIREG:
> +		if (igb_write_phy_reg(&adapter->hw, data->reg_num & 0x1F,
> +				     data->val_in))
> +			return -EIO;
> +		break;

A handful of drivers seem to expose this. What are the consequences of
exposing this ioctl? What can user space do with it?

It looks like a few drivers also check something like CAP_NET_ADMIN to
avoid allowing write access to all users. Is that enforced somewhere else?