From 7d2b554826195372764910da2f0dcb0d9b869108 Mon Sep 17 00:00:00 2001 From: Marek Lindner Date: Thu, 10 Feb 2011 14:33:50 +0000 Subject: [PATCH] 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 Signed-off-by: Marek Lindner --- net/batman-adv/soft-interface.c | 31 +++++++++++++++---------------- net/batman-adv/types.h | 2 +- 2 files changed, 16 insertions(+), 17 deletions(-) diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c index 7e37077ed81..152beaafae1 100644 --- a/net/batman-adv/soft-interface.c +++ b/net/batman-adv/soft-interface.c @@ -76,20 +76,18 @@ int my_skb_head_push(struct sk_buff *skb, unsigned int len) return 0; } -static void softif_neigh_free_ref(struct kref *refcount) +static void softif_neigh_free_rcu(struct rcu_head *rcu) { struct softif_neigh *softif_neigh; - softif_neigh = container_of(refcount, struct softif_neigh, refcount); + softif_neigh = container_of(rcu, struct softif_neigh, rcu); kfree(softif_neigh); } -static void softif_neigh_free_rcu(struct rcu_head *rcu) +static void softif_neigh_free_ref(struct softif_neigh *softif_neigh) { - struct softif_neigh *softif_neigh; - - softif_neigh = container_of(rcu, struct softif_neigh, rcu); - kref_put(&softif_neigh->refcount, softif_neigh_free_ref); + 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 @@ void softif_neigh_purge(struct bat_priv *bat_priv) 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 @@ static struct softif_neigh *softif_neigh_get(struct bat_priv *bat_priv, 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 @@ static struct softif_neigh *softif_neigh_get(struct bat_priv *bat_priv, 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 @@ static void softif_batman_recv(struct sk_buff *skb, struct net_device *dev, 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 @@ static void softif_batman_recv(struct sk_buff *skb, struct net_device *dev, } 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 cfbeb45cd9b..96f7c224975 100644 --- a/net/batman-adv/types.h +++ b/net/batman-adv/types.h @@ -268,7 +268,7 @@ struct softif_neigh { uint8_t addr[ETH_ALEN]; unsigned long last_seen; short vid; - struct kref refcount; + atomic_t refcount; struct rcu_head rcu; }; -- 2.20.1