On Wed, 16 Jan 2008 18:04:53 +0800
<[EMAIL PROTECTED]> wrote:
>
> In SMP, if a bridge fdb is being created when another CPU at the same time
> delete the bridge, this newly created fdb may incur a leakage:
>
> CPU0:
>
> static void del_nbp(struct net_bridge_port *p)
> {
> /*
> * CPU1 enter br_fdb_update(), bridge port is still valid.
> */
> ......
> spin_lock_bh(&br->lock);
> br_stp_disable_port(p);
> spin_unlock_bh(&br->lock);
>
> br_ifinfo_notify(RTM_DELLINK, p);
>
> br_fdb_delete_by_port(br, p, 1);
>
> /*
> * CPU1 call fdb_create() for the being deleted bridge,
> * a fdb would be add to bridge's fdb hash table, and will never
> * be freed. because when deleting a bridge, linux flush fdb for
> each
> * bridge port, but this newly created fdb belong to no bridge port
> */
> ......
> }
>
> To fix this, fdb_create() should be changed to:
> {
> struct net_bridge_fdb_entry *fdb;
>
> /*
> * if the bridge port is deleted, then return.
> */
> if (!(source->state == BR_STATE_LEARNING ||
> source->state == BR_STATE_FORWARDING))
> return;
>
> fdb = kmem_cache_alloc(br_fdb_cache, GFP_ATOMIC);
> if (fdb) {
> memcpy(fdb->addr.addr, addr, ETH_ALEN);
> atomic_set(&fdb->use_count, 1);
> hlist_add_head_rcu(&fdb->hlist, head);
>
> fdb->dst = source;
> fdb->is_local = is_local;
> fdb->is_static = is_local;
> fdb->ageing_timer = jiffies;
> }
> return fdb;
> }
>
That check is not enough, since the state might change during
fdb_create.
I think fdb_delete_by_port needs to be moved after RCU barrier event.
Something like this (untested) patch.
--- a/net/bridge/br_if.c 2008-01-16 11:00:09.000000000 -0800
+++ b/net/bridge/br_if.c 2008-01-16 11:01:11.000000000 -0800
@@ -116,6 +116,9 @@ static void destroy_nbp_rcu(struct rcu_h
{
struct net_bridge_port *p =
container_of(head, struct net_bridge_port, rcu);
+
+ br_fdb_delete_by_port(p->br, p, 1);
+
destroy_nbp(p);
}
@@ -143,8 +146,6 @@ static void del_nbp(struct net_bridge_po
br_ifinfo_notify(RTM_DELLINK, p);
- br_fdb_delete_by_port(br, p, 1);
-
list_del_rcu(&p->list);
rcu_assign_pointer(dev->br_port, NULL);
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