From: Hangbin Liu <liuhangbin@gmail.com>
Date: Tue, 20 Aug 2019 10:19:47 +0800
Subject: ipv6/addrconf: allow adding multicast addr if IFA_F_MCAUTOJOIN is set
Git-commit: f17f7648a49aa6728649ddf79bdbcac4f1970ce4
Patch-mainline: 5.3-rc7
References: networking-stable-19_08_28

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

[js] no cfg->ifa_flags in 4.12, use flags directly

Fixes: 93a714d6b53d ("multicast: Extend ip address command to enable multicast group join/leave on")
Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/ipv6/addrconf.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -967,7 +967,8 @@ ipv6_add_addr(struct inet6_dev *idev, co
 	int addr_type = ipv6_addr_type(addr);
 
 	if (addr_type == IPV6_ADDR_ANY ||
-	    addr_type & IPV6_ADDR_MULTICAST ||
+	    (addr_type & IPV6_ADDR_MULTICAST &&
+	     !(flags & IFA_F_MCAUTOJOIN)) ||
 	    (!(idev->dev->flags & IFF_LOOPBACK) &&
 	     addr_type & IPV6_ADDR_LOOPBACK))
 		return ERR_PTR(-EADDRNOTAVAIL);