linux-kernel - Re: [PATCH 1/2] veth: Initialize dev->perm

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Message-Id: <20200824.102545.1450838041398463071.davem@davemloft.net>
Date:   Mon, 24 Aug 2020 10:25:45 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     aranea@...ah.de
Cc:     kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] veth: Initialize dev->perm_addr

From: Mira Ressel <aranea@...ah.de>
Date: Mon, 24 Aug 2020 14:38:26 +0000

> Set the perm_addr of veth devices to whatever MAC has been assigned to
> the device. Otherwise, it remains all zero, with the consequence that
> ipv6_generate_stable_address() (which is used if the sysctl
> net.ipv6.conf.DEV.addr_gen_mode is set to 2 or 3) assigns every veth
> interface on a host the same link-local address.
> 
> The new behaviour matches that of several other virtual interface types
> (such as gre), and as far as I can tell, perm_addr isn't used by any
> other code sites that are relevant to veth.
> 
> Signed-off-by: Mira Ressel <aranea@...ah.de>
 ...
> @@ -1342,6 +1342,8 @@ static int veth_newlink(struct net *src_net, struct net_device *dev,
>  	if (!ifmp || !tbp[IFLA_ADDRESS])
>  		eth_hw_addr_random(peer);
>  
> +	memcpy(peer->perm_addr, peer->dev_addr, peer->addr_len);

Semantically don't you want to copy over the peer->perm_addr?

Otherwise this loses the entire point of the permanent address, and
what the ipv6 address generation facility expects.