net: bridge: fix a bug on using a neighbour cache entry without checking its state

[ Upstream commit 4c84edc11b76590859b1e45dd676074c59602dc4 ]

When handling DNAT'ed packets on a bridge device, the neighbour cache entry
from lookup was used without checking its state. It means that a cache entry
in the NUD_STALE state will be used directly instead of entering the NUD_DELAY
state to confirm the reachability of the neighbor.

This problem becomes worse after commit 2724680bceee ("neigh: Keep neighbour
cache entries if number of them is small enough."), since all neighbour cache
entries in the NUD_STALE state will be kept in the neighbour table as long as
the number of cache entries does not exceed the value specified in gc_thresh1.

This commit validates the state of a neighbour cache entry before using
the entry.

Signed-off-by: JianJhen Chen <kchen@synology.com>
Reviewed-by: JinLin Chen <jlchen@synology.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index f076a8ede00b4244e21d291a61093ba86973f104..6aec6b264f8e99ff3dbe39a9a048666a70d9c5f1 100644 (file)
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -287,7 +287,7 @@ static int br_nf_pre_routing_finish_bridge(struct sk_buff *skb)
        if (neigh) {
                int ret;
 
-               if (neigh->hh.hh_len) {
+               if ((neigh->nud_state & NUD_CONNECTED) && neigh->hh.hh_len) {
                        neigh_hh_bridge(&neigh->hh, skb);
                        skb->dev = nf_bridge->physindev;
                        ret = br_handle_frame_finish(skb);