netdev - [PATCH net 1/2] gre: Fix IPv6 multicast route creation.

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Message-ID: <027a923dcb550ad115e6d93ee8bb7d310378bd01.1752070620.git.gnault@redhat.com>
Date: Wed, 9 Jul 2025 16:30:10 +0200
From: Guillaume Nault <gnault@...hat.com>
To: David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, Simon Horman <horms@...nel.org>,
	David Ahern <dsahern@...nel.org>, Ido Schimmel <idosch@...dia.com>,
	Aiden Yang <ling@...dove.com>, Gary Guo <gary@...nel.org>
Subject: [PATCH net 1/2] gre: Fix IPv6 multicast route creation.

Use addrconf_add_dev() instead of ipv6_find_idev() in
addrconf_gre_config() so that we don't just get the inet6_dev, but also
install the default ff00::/8 multicast route.

Before commit 3e6a0243ff00 ("gre: Fix again IPv6 link-local address
generation."), the multicast route was created at the end of the
function by addrconf_add_mroute(). But this code path is now only taken
in one particular case (gre devices not bound to a local IP address and
in EUI64 mode). For all other cases, the function exits early and
addrconf_add_mroute() is not called anymore.

Using addrconf_add_dev() instead of ipv6_find_idev() in
addrconf_gre_config(), fixes the problem as it will create the default
multicast route for all gre devices. This also brings
addrconf_gre_config() a bit closer to the normal netdevice IPv6
configuration code (addrconf_dev_config()).

Fixes: 3e6a0243ff00 ("gre: Fix again IPv6 link-local address generation.")
Reported-by: Aiden Yang <ling@...dove.com>
Closes: https://lore.kernel.org/netdev/CANR=AhRM7YHHXVxJ4DmrTNMeuEOY87K2mLmo9KMed1JMr20p6g@mail.gmail.com/
Reviewed-by: Gary Guo <gary@...yguo.net>
Tested-by: Gary Guo <gary@...yguo.net>
Signed-off-by: Guillaume Nault <gnault@...hat.com>
---
 net/ipv6/addrconf.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index ba2ec7c870cc..870a0bd6c2ba 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3525,11 +3525,9 @@ static void addrconf_gre_config(struct net_device *dev)

 	ASSERT_RTNL();

-	idev = ipv6_find_idev(dev);
-	if (IS_ERR(idev)) {
-		pr_debug("%s: add_dev failed\n", __func__);
+	idev = addrconf_add_dev(dev);
+	if (IS_ERR(idev))
 		return;
-	}

 	/* Generate the IPv6 link-local address using addrconf_addr_gen(),
 	 * unless we have an IPv4 GRE device not bound to an IP address and
@@ -3543,9 +3541,6 @@ static void addrconf_gre_config(struct net_device *dev)
 	}

 	add_v4_addrs(idev);
-
-	if (dev->flags & IFF_POINTOPOINT)
-		addrconf_add_mroute(dev);
 }
 #endif

-- 
2.39.2