netdev - Re: [PATCHv2 net] ipv6/addrconf: allow adding multicast addr if IFA_F

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Date:   Wed, 21 Aug 2019 20:40:19 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     liuhangbin@...il.com
Cc:     netdev@...r.kernel.org, challa@...ronetworks.com,
        dsahern@...il.com, jishi@...hat.com
Subject: Re: [PATCHv2 net] ipv6/addrconf: allow adding multicast addr if
 IFA_F_MCAUTOJOIN is set

From: Hangbin Liu <liuhangbin@...il.com>
Date: Tue, 20 Aug 2019 10:19:47 +0800

> In commit 93a714d6b53d ("multicast: Extend ip address command to enable
> multicast group join/leave on") we added a new flag IFA_F_MCAUTOJOIN
> to make user able to add multicast address on ethernet interface.
> 
> This works for IPv4, but not for IPv6. See the inet6_addr_add code.
> 
> static int inet6_addr_add()
> {
> 	...
> 	if (cfg->ifa_flags & IFA_F_MCAUTOJOIN) {
> 		ipv6_mc_config(net->ipv6.mc_autojoin_sk, true...)
> 	}
> 
> 	ifp = ipv6_add_addr(idev, cfg, true, extack); <- always fail with maddr
> 	if (!IS_ERR(ifp)) {
> 		...
> 	} else if (cfg->ifa_flags & IFA_F_MCAUTOJOIN) {
> 		ipv6_mc_config(net->ipv6.mc_autojoin_sk, false...)
> 	}
> }
> 
> But in ipv6_add_addr() it will check the address type and reject multicast
> address directly. So this feature is never worked for IPv6.
> 
> We should not remove the multicast address check totally in ipv6_add_addr(),
> but could accept multicast address only when IFA_F_MCAUTOJOIN flag supplied.
> 
> v2: update commit description
> 
> Reported-by: Jianlin Shi <jishi@...hat.com>
> Fixes: 93a714d6b53d ("multicast: Extend ip address command to enable multicast group join/leave on")
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>

Applied and queued up for -stable.