Re: [PATCH] ppp: Add rtnl attribute IFLA_PPP_UNIT_ID for specifying ppp unit id

On Sat,  7 Aug 2021 18:37:49 +0200 Pali Rohár wrote:
> Currently there are two ways how to create a new ppp interface. Old method
> via ioctl(PPPIOCNEWUNIT) and new method via rtnl RTM_NEWLINK/NLM_F_CREATE
> which was introduced in v4.7 by commit 96d934c70db6 ("ppp: add rtnetlink
> device creation support").
> 
> ...

Your 2 previous patches were fixes and went into net, this patch seems
to be on top of them but is a feature, so should go to net-next. 
But it doesn't apply to net-next given net was not merged into net-next.
Please rebase on top of net-next or (preferably) wait until next week
so that the trees can get merged and then you can repost without causing
any conflicts.

>  static const struct nla_policy ppp_nl_policy[IFLA_PPP_MAX + 1] = {
>  	[IFLA_PPP_DEV_FD]	= { .type = NLA_S32 },
> +	[IFLA_PPP_UNIT_ID]	= { .type = NLA_S32 },
>  };

set .strict_start_type, please so new attrs get validated better

>  static int ppp_nl_validate(struct nlattr *tb[], struct nlattr *data[],
> @@ -1274,6 +1277,15 @@ static int ppp_nl_validate(struct nlattr *tb[], struct nlattr *data[],
>  
>  	if (!data[IFLA_PPP_DEV_FD])
>  		return -EINVAL;
> +
> +	/* Check for IFLA_PPP_UNIT_ID before IFLA_PPP_DEV_FD to allow userspace
> +	 * detect if kernel supports IFLA_PPP_UNIT_ID or not by specifying
> +	 * negative IFLA_PPP_DEV_FD. Previous kernel versions ignored
> +	 * IFLA_PPP_UNIT_ID attribute.
> +	 */
> +	if (data[IFLA_PPP_UNIT_ID] && nla_get_s32(data[IFLA_PPP_UNIT_ID]) < -1)
> +		return -EINVAL;

please use NLA_POLICY_MIN() instead, no need to open-code

>  	if (nla_get_s32(data[IFLA_PPP_DEV_FD]) < 0)
>  		return -EBADF;