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 51a82379ac5e9fd2f96a4f71783264459dddf98c..fe79bfc6d2dd17cce735757be9353789132911fe 100644 (file)
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -632,7 +632,19 @@ 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 8f7c778255fba74f51e9f84ad094c5beb492b0f9..7ac16d7b94a2f702231043fedbedd4e824371f73 100644 (file)
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -156,11 +156,14 @@ 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 965336a3b89d554364d40b45bbee8d25e6e3a714..7d47fe7534c184f36f396167bc3896120e9da6f0 100644 (file)
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -1566,6 +1566,12 @@ 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)