batman-adv: Disallow regular interface as mesh device

When trying to associate a net_device with another net_device which
already exists, batman-adv assumes that this interface is a fully
initialized batman mesh interface without checking it. The behaviour
when accessing data behind netdev_priv of a random net_device is
undefined and potentially dangerous.

Reported-by: Linus Lüssing <linus.luessing@ascom.ch>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>

3 files changed, 36 insertions, 12 deletions

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index 95a35b695700..b3058e46ee6b 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -79,13 +79,8 @@ static int is_valid_iface(struct net_device *net_dev)
                 return 0;
 
         /* no batman over batman */
-#ifdef HAVE_NET_DEVICE_OPS
-        if (net_dev->netdev_ops->ndo_start_xmit == interface_tx)
+        if (softif_is_valid(net_dev))
                 return 0;
-#else
-        if (net_dev->hard_start_xmit == interface_tx)
-                return 0;
-#endif
 
         /* Device is being bridged */
         /* if (net_dev->priv_flags & IFF_BRIDGE_PORT)
@@ -282,6 +277,8 @@ int hardif_enable_interface(struct hard_iface *hard_iface, char *iface_name)
 {
         struct bat_priv *bat_priv;
         struct batman_packet *batman_packet;
+        struct net_device *soft_iface;
+        int ret;
 
         if (hard_iface->if_status != IF_NOT_IN_USE)
                 goto out;
@@ -289,18 +286,30 @@ int hardif_enable_interface(struct hard_iface *hard_iface, char *iface_name)
         if (!atomic_inc_not_zero(&hard_iface->refcount))
                 goto out;
 
-        hard_iface->soft_iface = dev_get_by_name(&init_net, iface_name);
+        soft_iface = dev_get_by_name(&init_net, iface_name);
 
-        if (!hard_iface->soft_iface) {
-                hard_iface->soft_iface = softif_create(iface_name);
+        if (!soft_iface) {
+                soft_iface = softif_create(iface_name);
 
-                if (!hard_iface->soft_iface)
+                if (!soft_iface) {
+                        ret = -ENOMEM;
                         goto err;
+                }
 
                 /* dev_get_by_name() increases the reference counter for us */
-                dev_hold(hard_iface->soft_iface);
+                dev_hold(soft_iface);
+        }
+
+        if (!softif_is_valid(soft_iface)) {
+                pr_err("Can't create batman mesh interface %s: "
+                       "already exists as regular interface\n",
+                       soft_iface->name);
+                dev_put(soft_iface);
+                ret = -EINVAL;
+                goto err;
         }
 
+        hard_iface->soft_iface = soft_iface;
         bat_priv = netdev_priv(hard_iface->soft_iface);
         hard_iface->packet_len = BAT_PACKET_LEN;
         hard_iface->packet_buff = kmalloc(hard_iface->packet_len, GFP_ATOMIC);
@@ -308,6 +317,7 @@ int hardif_enable_interface(struct hard_iface *hard_iface, char *iface_name)
         if (!hard_iface->packet_buff) {
                 bat_err(hard_iface->soft_iface, "Can't add interface packet "
                         "(%s): out of memory\n", hard_iface->net_dev->name);
+                ret = -ENOMEM;
                 goto err;
         }
 
@@ -370,7 +380,7 @@ out:
 
 err:
         hardif_free_ref(hard_iface);
-        return -ENOMEM;
+        return ret;
 }
 
 void hardif_disable_interface(struct hard_iface *hard_iface)
diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 6b514ecee5a2..9ed26140a269 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -622,6 +622,19 @@ void softif_destroy(struct net_device *soft_iface)
         unregister_netdevice(soft_iface);
 }
 
+int softif_is_valid(struct net_device *net_dev)
+{
+#ifdef HAVE_NET_DEVICE_OPS
+        if (net_dev->netdev_ops->ndo_start_xmit == interface_tx)
+                return 1;
+#else
+        if (net_dev->hard_start_xmit == interface_tx)
+                return 1;
+#endif
+
+        return 0;
+}
+
 /* ethtool */
 static int bat_get_settings(struct net_device *dev, struct ethtool_cmd *cmd)
 {
diff --git a/net/batman-adv/soft-interface.h b/net/batman-adv/soft-interface.h
index 80a3607df186..4789b6f2a0b3 100644
--- a/net/batman-adv/soft-interface.h
+++ b/net/batman-adv/soft-interface.h
@@ -31,5 +31,6 @@ void interface_rx(struct net_device *soft_iface,
                   int hdr_size);
 struct net_device *softif_create(char *name);
 void softif_destroy(struct net_device *soft_iface);
+int softif_is_valid(struct net_device *net_dev);
 
 #endif /* _NET_BATMAN_ADV_SOFT_INTERFACE_H_ */