[PATCH 1/1] net: bridge: fix a bug on using a neighbour cache entry without checking its state

From: kchen
Date: Sat Jan 05 2019 - 22:35:41 EST

From: JianJhen Chen <kchen@xxxxxxxxxxxx>

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@xxxxxxxxxxxx>
Reviewed-by: JinLin Chen <jlchen@xxxxxxxxxxxx>
net/bridge/br_netfilter_hooks.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
index b1b5e85..ed683e5 100644
--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -278,7 +278,7 @@ int br_nf_pre_routing_finish_bridge(struct net *net, struct sock *sk, struct sk_
struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
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(net, sk, skb);