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[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 <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Patrick McHardy 2007-03-22 12:25:20 -07:00 committed by David S. Miller
parent ec25615b9d
commit b19cbe2a16
1 changed files with 2 additions and 2 deletions
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4
net/bridge/br_fdb.c
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@ -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;
}