ip6_gre: don't allow to remove the fb_tunnel_dev

It's possible to remove the FB tunnel with the command 'ip link del ip6gre0' but
this is unsafe, the module always supposes that this device exists. For example,
ip6gre_tunnel_lookup() may use it unconditionally.

Let's add a rtnl handler for dellink, which will never remove the FB tunnel (we
let ip6gre_destroy_tunnels() do the job).

Introduced by commit c12b395a4664 ("gre: Support GRE over IPv6").

CC: Dmitry Kozlov <xeb@mail.ru>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 0 deletions

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index c98338b81d30..9d921462b57f 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -1559,6 +1559,15 @@ static int ip6gre_changelink(struct net_device *dev, struct nlattr *tb[],
         return 0;
 }
 
+static void ip6gre_dellink(struct net_device *dev, struct list_head *head)
+{
+        struct net *net = dev_net(dev);
+        struct ip6gre_net *ign = net_generic(net, ip6gre_net_id);
+
+        if (dev != ign->fb_tunnel_dev)
+                unregister_netdevice_queue(dev, head);
+}
+
 static size_t ip6gre_get_size(const struct net_device *dev)
 {
         return
@@ -1636,6 +1645,7 @@ static struct rtnl_link_ops ip6gre_link_ops __read_mostly = {
         .validate       = ip6gre_tunnel_validate,
         .newlink        = ip6gre_newlink,
         .changelink     = ip6gre_changelink,
+        .dellink        = ip6gre_dellink,
         .get_size       = ip6gre_get_size,
         .fill_info      = ip6gre_fill_info,
 };