[PATCH net] ip6_vti: set netns_immutable on the fallback device.

[Eric Dumazet <edumazet@google.com>]

john1988 and Noam Rathaus reported that vti6_init_net() does not set the
netns_immutable flag on the per-netns fallback tunnel device (ip6_vti0).

Other similar tunnel drivers (like ip6_tunnel, sit, ip6_gre, and ip_tunnel)
correctly set this flag during their fallback device initialization to
prevent them from being moved to another network namespace.

Fixes: 61220ab34948 ("vti6: Enable namespace changing")
Reported-by: Noam Rathaus <noamr@ssd-disclosure.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/ipv6/ip6_vti.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index df793c8bfffb0a26ea7f54933b88bccc9b1aa495..d2b74a6f2cf62dbb752d8842e1a4d33fc8392d41 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -1159,6 +1159,7 @@ static int __net_init vti6_init_net(struct net *net)
 		goto err_alloc_dev;
 	dev_net_set(ip6n->fb_tnl_dev, net);
 	ip6n->fb_tnl_dev->rtnl_link_ops = &vti6_link_ops;
+	ip6n->fb_tnl_dev->netns_immutable = true;
 
 	err = vti6_fb_tnl_dev_init(ip6n->fb_tnl_dev);
 	if (err < 0)
-- 
2.54.0.1032.g2f8565e1d1-goog