[BRIDGE]: Fix fdb RCU race br_fdb_get use atomic_inc to increase the refcount of an element found on a RCU protected list, which can lead to the following race: CPU0 CPU1 br_fdb_get: rcu_read_lock __br_fdb_get: find element fdb_delete: hlist_del_rcu br_fdb_put br_fdb_put: atomic_dec_and_test call_rcu(fdb_rcu_free) br_fdb_get: atomic_inc rcu_read_unlock fdb_rcu_free: kmem_cache_free Use atomic_inc_not_zero instead. Signed-off-by: Patrick McHardy --- commit 6965873e9db0cb3f9a8412bd541a5309dcfb6eb6 tree 152e90dc86fe96ca7cb8f0e280827920ddb62247 parent 8559840c4ca3f2fff73a882803bc8916078fac1f author Patrick McHardy Thu, 22 Mar 2007 19:20:08 +0100 committer Patrick McHardy Thu, 22 Mar 2007 19:20:08 +0100 net/bridge/br_fdb.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c index def2e40..8d566c1 100644 --- a/net/bridge/br_fdb.c +++ b/net/bridge/br_fdb.c @@ -197,8 +197,8 @@ struct net_bridge_fdb_entry *br_fdb_get(struct net_bridge *br, rcu_read_lock(); fdb = __br_fdb_get(br, addr); - if (fdb) - atomic_inc(&fdb->use_count); + if (fdb && !atomic_inc_not_zero(&fdb->use_count)) + fdb = NULL; rcu_read_unlock(); return fdb; }