[PATCH net] bridge: clean the nf_bridge status when forwarding the skb

[Antonio Quartulli <antonio@meshcoding.com>]

From: Antonio Quartulli <antonio@open-mesh.com>

Even if it is forbidden to enslave a bridge interface into
another one, it is still possible to create a chain of
virtual interfaces including two distinct bridges.

In this case, the skb entering the second bridge could have
the nf_bridge field already set due to a previous operation
and consequently lead to wrong a processing of the packet
itself.

To prevent this behaviour release and set to NULL the
nf_bridge field of the skb when forwarding the packet.

Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Antonio Quartulli <antonio@open-mesh.com>
---

I know that not using "extern" when declaring the prototype is not consistent
with the surrounding code, but checkpatch complaints about using "extern" in .h
file and I prefer to not do something "wrong" even if stylistically ugly.

Cheers,


 net/bridge/br_forward.c   |  2 ++
 net/bridge/br_netfilter.c | 10 ++++++++++
 net/bridge/br_private.h   |  2 ++
 3 files changed, 14 insertions(+)

diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index 4b81b14..62955f3 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -49,6 +49,8 @@ int br_dev_queue_push_xmit(struct sk_buff *skb)
 	} else {
 		skb_push(skb, ETH_HLEN);
 		br_drop_fake_rtable(skb);
+		br_netfilter_skb_free(skb);
+
 		dev_queue_xmit(skb);
 	}
 
diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index f877362..7cad3e2 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -1086,3 +1086,13 @@ void br_netfilter_fini(void)
 #endif
 	dst_entries_destroy(&fake_dst_ops);
 }
+
+/**
+ * br_netfilter_skb_free - clean the NF bridge data in an skb
+ * @skb: the skb which the data to free belongs to
+ */
+void br_netfilter_skb_free(struct sk_buff *skb)
+{
+	nf_bridge_put(skb->nf_bridge);
+	skb->nf_bridge = NULL;
+}
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index efb57d9..2a5f637 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -730,10 +730,12 @@ static inline u16 br_get_pvid(const struct net_port_vlans *v)
 extern int br_netfilter_init(void);
 extern void br_netfilter_fini(void);
 extern void br_netfilter_rtable_init(struct net_bridge *);
+void br_netfilter_skb_free(struct sk_buff *skb);
 #else
 #define br_netfilter_init()	(0)
 #define br_netfilter_fini()	do { } while(0)
 #define br_netfilter_rtable_init(x)
+#define br_netfilter_skb_free(x)
 #endif
 
 /* br_stp.c */
-- 
1.8.3.2