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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jianlin Shi <jishi@redhat.com>,
        Hangbin Liu <liuhangbin@gmail.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.2 049/143] ipv6/addrconf: allow adding multicast addr if IFA_F_MCAUTOJOIN is set
Date:   Wed,  4 Sep 2019 19:53:12 +0200
Message-Id: <20190904175315.989326532@linuxfoundation.org>
In-Reply-To: <20190904175314.206239922@linuxfoundation.org>
References: <20190904175314.206239922@linuxfoundation.org>
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From: Hangbin Liu <liuhangbin@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 <jishi@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/addrconf.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1045,7 +1045,8 @@ 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) &&
 	     !netif_is_l3_master(idev->dev) &&
 	     addr_type & IPV6_ADDR_LOOPBACK))