batman-adv: Don't increase MTU when set by user

commit d8e42a2b0addf238be8b3b37dcd9795a5c1be459 upstream.

If the user set an MTU value, it usually means that there are special
requirements for the MTU. But if an interface gots activated, the MTU was
always recalculated and then the user set value was overwritten.

The only reason why this user set value has to be overwritten, is when the
MTU has to be decreased because batman-adv is not able to transfer packets
with the user specified size.

Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol")
Cc: stable@vger.kernel.org
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index ae5762af0146763215b500b3ecbb4590a3901f88..24c9c0c3f3166f66d5696175fe8dd55f1fdce8c7 100644 (file)
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -630,7 +630,19 @@ out:
  */
 void batadv_update_min_mtu(struct net_device *soft_iface)
 {
-       dev_set_mtu(soft_iface, batadv_hardif_min_mtu(soft_iface));
+       struct batadv_priv *bat_priv = netdev_priv(soft_iface);
+       int limit_mtu;
+       int mtu;
+
+       mtu = batadv_hardif_min_mtu(soft_iface);
+
+       if (bat_priv->mtu_set_by_user)
+               limit_mtu = bat_priv->mtu_set_by_user;
+       else
+               limit_mtu = ETH_DATA_LEN;
+
+       mtu = min(mtu, limit_mtu);
+       dev_set_mtu(soft_iface, mtu);
 
        /* Check if the local translate table should be cleaned up to match a
         * new (and smaller) MTU.

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 0f5c0679b55a296603282aa5c7047d7dc6c95234..38d411a52f3315232bb16fe6c6445fa0abc92e41 100644 (file)
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -154,11 +154,14 @@ static int batadv_interface_set_mac_addr(struct net_device *dev, void *p)
 
 static int batadv_interface_change_mtu(struct net_device *dev, int new_mtu)
 {
+       struct batadv_priv *bat_priv = netdev_priv(dev);
+
        /* check ranges */
        if (new_mtu < 68 || new_mtu > batadv_hardif_min_mtu(dev))
                return -EINVAL;
 
        dev->mtu = new_mtu;
+       bat_priv->mtu_set_by_user = new_mtu;
 
        return 0;
 }

diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index 758cd797a063b565ef1d2512793020db90374624..76791815b26ba46540d32a2053ed61c5cc7757d6 100644 (file)
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -1546,6 +1546,12 @@ struct batadv_priv {
        /** @soft_iface: net device which holds this struct as private data */
        struct net_device *soft_iface;
 
+       /**
+        * @mtu_set_by_user: MTU was set once by user
+        * protected by rtnl_lock
+        */
+       int mtu_set_by_user;
+
        /**
         * @bat_counters: mesh internal traffic statistic counters (see
         *  batadv_counters)