netdev - Re: [PATCH net] bareudp: Disallow udp port 0.

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Date:   Thu, 30 Jul 2020 16:20:30 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Martin Varghese <martinvarghesenokia@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jbenc@...hat.com,
        gnault@...hat.com, Martin Varghese <martin.varghese@...ia.com>
Subject: Re: [PATCH net] bareudp: Disallow udp port 0.

On Thu, 30 Jul 2020 22:33:51 +0530 Martin Varghese wrote:
> From: Martin Varghese <martin.varghese@...ia.com>
> 
> Kernel does not support udp destination port 0 on wire. Hence
> bareudp device with udp destination port 0 must be disallowed.
> 
> Fixes: 571912c69f0e ("net: UDP tunnel encapsulation module for tunnelling different protocols like MPLS, IP, NSH etc.")
> Signed-off-by: Martin Varghese <martin.varghese@...ia.com>
> ---
>  drivers/net/bareudp.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/bareudp.c b/drivers/net/bareudp.c
> index 88e7900853db..08b195d32cbe 100644
> --- a/drivers/net/bareudp.c
> +++ b/drivers/net/bareudp.c
> @@ -578,8 +578,13 @@ static int bareudp2info(struct nlattr *data[], struct bareudp_conf *conf,
>  		return -EINVAL;
>  	}
>  
> -	if (data[IFLA_BAREUDP_PORT])
> +	if (data[IFLA_BAREUDP_PORT]) {
>  		conf->port =  nla_get_u16(data[IFLA_BAREUDP_PORT]);
> +		if (!conf->port) {
> +			NL_SET_ERR_MSG(extack, "udp port 0 not supported");
> +			return -EINVAL;
> +		}
> +	}

Please use one of the NLA_POLICY_**-ies, probably NLA_POLICY_MIN() ? 
That's better for documenting, exporting for user space, and will also
point the user space to the attribute in exack automatically.