batman-adv: Request iflink once in batadv_get_real_netdevice

There is no need to call dev_get_iflink multiple times for the same
net_device in batadv_get_real_netdevice. And since some of the
ndo_get_iflink callbacks are dynamic (for example via RCUs like in
vxcan_get_iflink), it could easily happen that the returned values are not
stable. The pre-checks before __dev_get_by_index are then of course bogus.

Fixes: 5ed4a460a1d3 ("batman-adv: additional checks for virtual interfaces on top of WiFi")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index 35aa1122043b642ac4acdd5cbd805b9c8398efd3..e2760cfce1909f2a2b4aec589759dbe4a82bdf7e 100644 (file)
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -215,14 +215,16 @@ static struct net_device *batadv_get_real_netdevice(struct net_device *netdev)
        struct net_device *real_netdev = NULL;
        struct net *real_net;
        struct net *net;
-       int ifindex;
+       int iflink;
 
        ASSERT_RTNL();
 
        if (!netdev)
                return NULL;
 
-       if (netdev->ifindex == dev_get_iflink(netdev)) {
+       iflink = dev_get_iflink(netdev);
+
+       if (netdev->ifindex == iflink) {
                dev_hold(netdev);
                return netdev;
        }
@@ -232,9 +234,8 @@ static struct net_device *batadv_get_real_netdevice(struct net_device *netdev)
                goto out;
 
        net = dev_net(hard_iface->soft_iface);
-       ifindex = dev_get_iflink(netdev);
        real_net = batadv_getlink_net(netdev, net);
-       real_netdev = dev_get_by_index(real_net, ifindex);
+       real_netdev = dev_get_by_index(real_net, iflink);
 
 out:
        batadv_hardif_put(hard_iface);