netdev - Re: [PATCH net-next 2/2] net: limit altnames to 64k total

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Date:   Wed, 9 Mar 2022 19:51:07 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, jiri@...nulli.us,
        George Shuklin <george.shuklin@...il.com>
Subject: Re: [PATCH net-next 2/2] net: limit altnames to 64k total

On 3/9/22 11:29 AM, Jakub Kicinski wrote:
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index aa05e89cc47c..159c9c61e6af 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -3652,12 +3652,23 @@ static int rtnl_alt_ifname(int cmd, struct net_device *dev, struct nlattr *attr,
>  			   bool *changed, struct netlink_ext_ack *extack)
>  {
>  	char *alt_ifname;
> +	size_t size;
>  	int err;
>  
>  	err = nla_validate(attr, attr->nla_len, IFLA_MAX, ifla_policy, extack);
>  	if (err)
>  		return err;
>  
> +	if (cmd == RTM_NEWLINKPROP) {
> +		size = rtnl_prop_list_size(dev);
> +		size += nla_total_size(ALTIFNAMSIZ);
> +		if (size >= U16_MAX) {
> +			NL_SET_ERR_MSG(extack,
> +				       "effective property list too long");
> +			return -EINVAL;
> +		}
> +	}
> +
>  	alt_ifname = nla_strdup(attr, GFP_KERNEL_ACCOUNT);
>  	if (!alt_ifname)
>  		return -ENOMEM;

this tests the existing property size. Don't you want to test the size
with the alt_ifname - does it make the list go over 64kB?