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Date:   Tue, 26 Mar 2019 12:46:46 -0700 (PDT)
Message-Id: <20190326.124646.505432518345625779.davem@davemloft.net>
To:     mkubecek@suse.cz
Cc:     netdev@vger.kernel.org, jakub.kicinski@netronome.com,
        jiri@resnulli.us, andrew@lunn.ch, f.fainelli@gmail.com,
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        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next v5 01/22] rtnetlink: provide permanent
 hardware address in RTM_NEWLINK
From:   David Miller <davem@davemloft.net>
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        <16ffb1fbfa8f54de587ac52f4ff95e5034c590b4.1553532199.git.mkubecek@suse.cz>
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From: Michal Kubecek <mkubecek@suse.cz>
Date: Mon, 25 Mar 2019 18:07:57 +0100 (CET)

> @@ -1683,6 +1684,8 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
>  	    nla_put_s32(skb, IFLA_NEW_IFINDEX, new_ifindex) < 0)
>  		goto nla_put_failure;
>  
> +	if (nla_put(skb, IFLA_PERM_ADDRESS, dev->addr_len, dev->perm_addr))
> +		goto nla_put_failure;
>  
>  	rcu_read_lock();
>  	if (rtnl_fill_link_af(skb, dev, ext_filter_mask))

I guess, as Jiri says, we really do have to check if the driver
actually set this before pushing the attribute out to userspace.

But seriously, you chould just check for dev_addr_len zeros.

All zeros is not a valid link address on any link type.