[PATCH 4.19 34/93] ipv6/addrconf: allow adding multicast addr if IFA_F_MCAUTOJOIN is set

[Greg Kroah-Hartman]

From: Hangbin Liu <liuhang...@gmail.com>

[ Upstream commit f17f7648a49aa6728649ddf79bdbcac4f1970ce4 ]

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

Fixes: 93a714d6b53d ("multicast: Extend ip address command to enable multicast 
group join/leave on")
Reported-by: Jianlin Shi <ji...@redhat.com>
Signed-off-by: Hangbin Liu <liuhang...@gmail.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/ipv6/addrconf.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -995,7 +995,8 @@ ipv6_add_addr(struct inet6_dev *idev, st
        int err = 0;
 
        if (addr_type == IPV6_ADDR_ANY ||
-           addr_type & IPV6_ADDR_MULTICAST ||
+           (addr_type & IPV6_ADDR_MULTICAST &&
+            !(cfg->ifa_flags & IFA_F_MCAUTOJOIN)) ||
            (!(idev->dev->flags & IFF_LOOPBACK) &&
             addr_type & IPV6_ADDR_LOOPBACK))
                return ERR_PTR(-EADDRNOTAVAIL);