Linux Ethernet Bridging - Nov 2007 - [PATCH (resubmit)][BRIDGE] Properly dereference the br_should_route_hook

This hook is protected with the RCU, so simple

	if (br_should_route_hook)
		br_should_route_hook(...)

is not enough on some architectures.

Use the rcu_dereference/rcu_assign_pointer in this case.

Fixed Stephen's comment concerning using the typeof().

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

---

diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index 3cedd4e..0ee79a7 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -122,6 +122,7 @@ static inline int is_link_local(const unsigned char *dest)
 struct sk_buff *br_handle_frame(struct net_bridge_port *p, struct sk_buff *skb)
 {
 	const unsigned char *dest = eth_hdr(skb)->h_dest;
+	int (*rhook)(struct sk_buff *skb);
 
 	if (!is_valid_ether_addr(eth_hdr(skb)->h_source))
 		goto drop;
@@ -147,9 +148,9 @@ struct sk_buff *br_handle_frame(struct net_bridge_port *p,
struct sk_buff *skb)
 
 	switch (p->state) {
 	case BR_STATE_FORWARDING:
-
-		if (br_should_route_hook) {
-			if (br_should_route_hook(skb))
+		rhook = rcu_dereference(br_should_route_hook);
+		if (rhook != NULL) {
+			if (rhook(skb))
 				return skb;
 			dest = eth_hdr(skb)->h_dest;
 		}
diff --git a/net/bridge/netfilter/ebtable_broute.c
b/net/bridge/netfilter/ebtable_broute.c
index e44519e..be6f186 100644
--- a/net/bridge/netfilter/ebtable_broute.c
+++ b/net/bridge/netfilter/ebtable_broute.c
@@ -70,13 +70,13 @@ static int __init ebtable_broute_init(void)
 	if (ret < 0)
 		return ret;
 	/* see br_input.c */
-	br_should_route_hook = ebt_broute;
+	rcu_assign_pointer(br_should_route_hook, ebt_broute);
 	return ret;
 }
 
 static void __exit ebtable_broute_fini(void)
 {
-	br_should_route_hook = NULL;
+	rcu_assign_pointer(br_should_route_hook, NULL);
 	synchronize_net();
 	ebt_unregister_table(&broute_table);
 }

On Tue, Nov 27, 2007 at 07:21:08PM +0300, Pavel Emelyanov
wrote:
> This hook is protected with the RCU, so simple
> 
> 	if (br_should_route_hook)
> 		br_should_route_hook(...)
> 
> is not enough on some architectures.
> 
> Use the rcu_dereference/rcu_assign_pointer in this case.
> 
> Fixed Stephen's comment concerning using the typeof().
> 
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Applied to net-2.6.  Thanks Pavel!
>  static void __exit ebtable_broute_fini(void)
>  {
> -	br_should_route_hook = NULL;
> +	rcu_assign_pointer(br_should_route_hook, NULL);
Just for the record, rcu_assign_pointer is never necessary when
you're assigning NULL.  The reason is that rcu_assign_pointer serves
as a barrier between the initialisation of the content of what you're
assigning and the actual assignment.  Since NULL does not need to be
initialised you don't need the barrier :)

Hmm, perhaps we could even build this logic into rcu_assign_pointer.

Then again, who still uses an Alpha? Mine died years ago :)

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt