Commit 4e914ef0 authored Jul 09, 2025 by Guillaume Nault Committed by Jakub Kicinski Jul 10, 2025

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 3e6a0243 ("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()).

Cc: stable@vger.kernel.org
Fixes: 3e6a0243 ("gre: Fix again IPv6 link-local address generation.")
Reported-by: Aiden Yang <ling@moedove.com>
Closes: https://lore.kernel.org/netdev/CANR=AhRM7YHHXVxJ4DmrTNMeuEOY87K2mLmo9KMed1JMr20p6g@mail.gmail.com/


Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/027a923dcb550ad115e6d93ee8bb7d310378bd01.1752070620.git.gnault@redhat.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

parent 2dfa4e31

net/ipv6/addrconf.c

+2 −7

Original line number	Diff line number	Diff line
		@@ -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