gre: don't allow to add the same tunnel twice

Before the patch, it was possible to add two times the same tunnel:
ip l a gre1 type gre remote local
ip l a gre2 type gre remote local

It was possible, because ip_tunnel_newlink() calls ip_tunnel_find() with the
argument dev->type, which was set only later (when calling ndo_init handler
in register_netdevice()). Let's set this type in the setup handler, which is
called before newlink handler.

Introduced by commit c54419321455 ("GRE: Refactor GRE tunneling code.").

CC: Pravin B Shelar <>
Signed-off-by: Nicolas Dichtel <>
Signed-off-by: David S. Miller <>
1 file changed