Re: [PATCHv2 net] ipv6/addrconf: call ipv6_mc_up() for non-Ethernet interface

[David Miller <davem@davemloft.net>]

From: Hangbin Liu <liuhangbin@gmail.com>
Date: Tue, 10 Mar 2020 15:27:37 +0800

> Rafał found an issue that for non-Ethernet interface, if we down and up
> frequently, the memory will be consumed slowly.
> 
> The reason is we add allnodes/allrouters addressed in multicast list in
> ipv6_add_dev(). When link down, we call ipv6_mc_down(), store all multicast
> addresses via mld_add_delrec(). But when link up, we don't call ipv6_mc_up()
> for non-Ethernet interface to remove the addresses. This makes idev->mc_tomb
> getting bigger and bigger. The call stack looks like:
> 
> addrconf_notify(NETDEV_REGISTER)
> 	ipv6_add_dev
> 		ipv6_dev_mc_inc(ff01::1)
> 		ipv6_dev_mc_inc(ff02::1)
> 		ipv6_dev_mc_inc(ff02::2)
> 
> addrconf_notify(NETDEV_UP)
> 	addrconf_dev_config
> 		/* Alas, we support only Ethernet autoconfiguration. */
> 		return;
> 
> addrconf_notify(NETDEV_DOWN)
> 	addrconf_ifdown
> 		ipv6_mc_down
> 			igmp6_group_dropped(ff02::2)
> 				mld_add_delrec(ff02::2)
> 			igmp6_group_dropped(ff02::1)
> 			igmp6_group_dropped(ff01::1)
> 
> After investigating, I can't found a rule to disable multicast on
> non-Ethernet interface. In RFC2460, the link could be Ethernet, PPP, ATM,
> tunnels, etc. In IPv4, it doesn't check the dev type when calls ip_mc_up()
> in inetdev_event(). Even for IPv6, we don't check the dev type and call
> ipv6_add_dev(), ipv6_dev_mc_inc() after register device.
> 
> So I think it's OK to fix this memory consumer by calling ipv6_mc_up() for
> non-Ethernet interface.
> 
> v2: Also check IFF_MULTICAST flag to make sure the interface supports
>     multicast
> 
> Reported-by: Rafał Miłecki <zajec5@gmail.com>
> Fixes: 74235a25c673 ("[IPV6] addrconf: Fix IPv6 on tuntap tunnels")
> Fixes: 1666d49e1d41 ("mld: do not remove mld souce list info when set link down")
> Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>

Applied and queued up for -stable, thank you.