batman-adv: Correct rcu refcounting for softif_neigh
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/soft-interface.c b/net/batman-adv/soft-interface.c
index 7e37077..152beaa 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -76,20 +76,18 @@
return 0;
}
-static void softif_neigh_free_ref(struct kref *refcount)
-{
- struct softif_neigh *softif_neigh;
-
- softif_neigh = container_of(refcount, struct softif_neigh, refcount);
- kfree(softif_neigh);
-}
-
static void softif_neigh_free_rcu(struct rcu_head *rcu)
{
struct softif_neigh *softif_neigh;
softif_neigh = container_of(rcu, struct softif_neigh, rcu);
- kref_put(&softif_neigh->refcount, softif_neigh_free_ref);
+ kfree(softif_neigh);
+}
+
+static void softif_neigh_free_ref(struct softif_neigh *softif_neigh)
+{
+ if (atomic_dec_and_test(&softif_neigh->refcount))
+ call_rcu(&softif_neigh->rcu, softif_neigh_free_rcu);
}
void softif_neigh_purge(struct bat_priv *bat_priv)
@@ -116,11 +114,10 @@
softif_neigh->addr, softif_neigh->vid);
softif_neigh_tmp = bat_priv->softif_neigh;
bat_priv->softif_neigh = NULL;
- kref_put(&softif_neigh_tmp->refcount,
- softif_neigh_free_ref);
+ softif_neigh_free_ref(softif_neigh_tmp);
}
- call_rcu(&softif_neigh->rcu, softif_neigh_free_rcu);
+ softif_neigh_free_ref(softif_neigh);
}
spin_unlock_bh(&bat_priv->softif_neigh_lock);
@@ -141,8 +138,11 @@
if (softif_neigh->vid != vid)
continue;
+ if (!atomic_inc_not_zero(&softif_neigh->refcount))
+ continue;
+
softif_neigh->last_seen = jiffies;
- goto found;
+ goto out;
}
softif_neigh = kzalloc(sizeof(struct softif_neigh), GFP_ATOMIC);
@@ -152,15 +152,14 @@
memcpy(softif_neigh->addr, addr, ETH_ALEN);
softif_neigh->vid = vid;
softif_neigh->last_seen = jiffies;
- kref_init(&softif_neigh->refcount);
+ /* initialize with 2 - caller decrements counter by one */
+ atomic_set(&softif_neigh->refcount, 2);
INIT_HLIST_NODE(&softif_neigh->list);
spin_lock_bh(&bat_priv->softif_neigh_lock);
hlist_add_head_rcu(&softif_neigh->list, &bat_priv->softif_neigh_list);
spin_unlock_bh(&bat_priv->softif_neigh_lock);
-found:
- kref_get(&softif_neigh->refcount);
out:
rcu_read_unlock();
return softif_neigh;
@@ -264,7 +263,7 @@
softif_neigh->addr, softif_neigh->vid);
softif_neigh_tmp = bat_priv->softif_neigh;
bat_priv->softif_neigh = softif_neigh;
- kref_put(&softif_neigh_tmp->refcount, softif_neigh_free_ref);
+ softif_neigh_free_ref(softif_neigh_tmp);
/* we need to hold the additional reference */
goto err;
}
@@ -282,7 +281,7 @@
}
out:
- kref_put(&softif_neigh->refcount, softif_neigh_free_ref);
+ softif_neigh_free_ref(softif_neigh);
err:
kfree_skb(skb);
return;
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index cfbeb45..96f7c22 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -268,7 +268,7 @@
uint8_t addr[ETH_ALEN];
unsigned long last_seen;
short vid;
- struct kref refcount;
+ atomic_t refcount;
struct rcu_head rcu;
};