netdev - Re: [RFC] ipv6: use a random ifid for headerless devices

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Date:	Mon, 30 Nov 2015 21:01:32 +0900
From:	吉藤英明 <hideaki.yoshifuji@...aclelinux.com>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	network dev <netdev@...r.kernel.org>
Subject: Re: [RFC] ipv6: use a random ifid for headerless devices

Hi,

2015-11-30 20:55 GMT+09:00 Bjørn Mork <bjorn@...k.no>:
> Generating a random ifid for devices with no L2 header
> at all, allowing such devices to take part in IPv6
> autoconfiguration. The tuntap driver is one example of
> a driver where such an ifid would be useful.
>
> Note that as there is no persistence, new addresses
> will be generated every time an interface is brought up:
>
>  # ip -6 addr show dev tun0
>  8: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 500
>      inet6 fe80::eef2:111c:f270:92ba/64 scope link
>         valid_lft forever preferred_lft forever
>  # ip link set tun0 down
>  # ip link set tun0 up
>  # ip -6 addr show dev tun0
>  8: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 500
>      inet6 fe80::eec0:48d0:6b52:8835/64 scope link
>         valid_lft forever preferred_lft forever
>
> Signed-off-by: Bjørn Mork <bjorn@...k.no>
> ---
> I'm planning raw-ip support for the qmi_wwan driver.  And
> the feedback from primary users (ModemManager++) is that
> a headerless netdev is preferred over a fake ethernet
> device. The current plan is to model this after 'tun'
> devices, using ARPHRD_NONE as type.
>
> But these devices will need an IPv6 link local address for
> full SLAAC support.  I am therefore wondering if an approach
> like this patch will be acceptable, or if I should look for
> some other solution?
>
>
>
> Bjørn
>
>
>  net/ipv6/addrconf.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index d84742f003a9..6cf3cae691a5 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -53,6 +53,7 @@
>  #include <linux/if_arp.h>
>  #include <linux/if_arcnet.h>
>  #include <linux/if_infiniband.h>
> +#include <linux/random.h>
>  #include <linux/route.h>
>  #include <linux/inetdevice.h>
>  #include <linux/init.h>
> @@ -2026,6 +2027,13 @@ static int addrconf_ifid_ip6tnl(u8 *eui, struct net_device *dev)
>         return 0;
>  }
>
> +static int addrconf_ifid_random(u8 *eui, struct net_device *dev)
> +{
> +       get_random_bytes(eui, 8);
> +       eui[0] |= 0x02;
> +       return 0;
> +}
> +

Since random identifier is locally assigned, drop the global bit
instead if setting it.

--yoshfuji
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