batman-adv: Correct rcu refcounting for batman_if
It might be possible that 2 threads access the same data in the same
rcu grace period. The first thread calls call_rcu() to decrement the
refcount and free the data while the second thread increases the
refcount to use the data. To avoid this race condition all refcount
operations have to be atomic.
Reported-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index e2b001a..8982485 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -40,13 +40,13 @@
struct packet_type *ptype,
struct net_device *orig_dev);
-static void hardif_free_rcu(struct rcu_head *rcu)
+void hardif_free_rcu(struct rcu_head *rcu)
{
struct batman_if *batman_if;
batman_if = container_of(rcu, struct batman_if, rcu);
dev_put(batman_if->net_dev);
- kref_put(&batman_if->refcount, hardif_free_ref);
+ kfree(batman_if);
}
struct batman_if *get_batman_if_by_netdev(struct net_device *net_dev)
@@ -55,16 +55,14 @@
rcu_read_lock();
list_for_each_entry_rcu(batman_if, &if_list, list) {
- if (batman_if->net_dev == net_dev)
+ if (batman_if->net_dev == net_dev &&
+ atomic_inc_not_zero(&batman_if->refcount))
goto out;
}
batman_if = NULL;
out:
- if (batman_if)
- kref_get(&batman_if->refcount);
-
rcu_read_unlock();
return batman_if;
}
@@ -105,16 +103,14 @@
if (batman_if->soft_iface != soft_iface)
continue;
- if (batman_if->if_status == IF_ACTIVE)
+ if (batman_if->if_status == IF_ACTIVE &&
+ atomic_inc_not_zero(&batman_if->refcount))
goto out;
}
batman_if = NULL;
out:
- if (batman_if)
- kref_get(&batman_if->refcount);
-
rcu_read_unlock();
return batman_if;
}
@@ -137,14 +133,14 @@
struct batman_packet *batman_packet;
struct batman_if *old_if;
- if (batman_if)
- kref_get(&batman_if->refcount);
+ if (batman_if && !atomic_inc_not_zero(&batman_if->refcount))
+ batman_if = NULL;
old_if = bat_priv->primary_if;
bat_priv->primary_if = batman_if;
if (old_if)
- kref_put(&old_if->refcount, hardif_free_ref);
+ hardif_free_ref(old_if);
if (!bat_priv->primary_if)
return;
@@ -290,6 +286,9 @@
if (batman_if->if_status != IF_NOT_IN_USE)
goto out;
+ if (!atomic_inc_not_zero(&batman_if->refcount))
+ goto out;
+
batman_if->soft_iface = dev_get_by_name(&init_net, iface_name);
if (!batman_if->soft_iface) {
@@ -328,7 +327,6 @@
batman_if->batman_adv_ptype.type = __constant_htons(ETH_P_BATMAN);
batman_if->batman_adv_ptype.func = batman_skb_recv;
batman_if->batman_adv_ptype.dev = batman_if->net_dev;
- kref_get(&batman_if->refcount);
dev_add_pack(&batman_if->batman_adv_ptype);
atomic_set(&batman_if->seqno, 1);
@@ -371,6 +369,7 @@
return 0;
err:
+ hardif_free_ref(batman_if);
return -ENOMEM;
}
@@ -387,7 +386,6 @@
bat_info(batman_if->soft_iface, "Removing interface: %s\n",
batman_if->net_dev->name);
dev_remove_pack(&batman_if->batman_adv_ptype);
- kref_put(&batman_if->refcount, hardif_free_ref);
bat_priv->num_ifaces--;
orig_hash_del_if(batman_if, bat_priv->num_ifaces);
@@ -399,7 +397,7 @@
set_primary_if(bat_priv, new_if);
if (new_if)
- kref_put(&new_if->refcount, hardif_free_ref);
+ hardif_free_ref(new_if);
}
kfree(batman_if->packet_buff);
@@ -416,6 +414,7 @@
softif_destroy(batman_if->soft_iface);
batman_if->soft_iface = NULL;
+ hardif_free_ref(batman_if);
}
static struct batman_if *hardif_add_interface(struct net_device *net_dev)
@@ -445,7 +444,8 @@
batman_if->soft_iface = NULL;
batman_if->if_status = IF_NOT_IN_USE;
INIT_LIST_HEAD(&batman_if->list);
- kref_init(&batman_if->refcount);
+ /* extra reference for return */
+ atomic_set(&batman_if->refcount, 2);
check_known_mac_addr(batman_if->net_dev);
@@ -453,8 +453,6 @@
list_add_tail_rcu(&batman_if->list, &if_list);
spin_unlock(&if_list_lock);
- /* extra reference for return */
- kref_get(&batman_if->refcount);
return batman_if;
free_if:
@@ -476,7 +474,7 @@
batman_if->if_status = IF_TO_BE_REMOVED;
sysfs_del_hardif(&batman_if->hardif_obj);
- call_rcu(&batman_if->rcu, hardif_free_rcu);
+ hardif_free_ref(batman_if);
}
void hardif_remove_interfaces(void)
@@ -548,7 +546,7 @@
};
hardif_put:
- kref_put(&batman_if->refcount, hardif_free_ref);
+ hardif_free_ref(batman_if);
out:
return NOTIFY_DONE;
}