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

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

[kchen]

From: JianJhen Chen <kchen@synology.com>

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>
---
 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);
-- 
2.7.4

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

[David Miller]

From: kchen <kchen@synology.com>
Date: Sun,  6 Jan 2019 11:28:13 +0800

> From: JianJhen Chen <kchen@synology.com>
> 
> 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>

Indeed, this looks correct.

Applied and queued up for -stable, thanks.

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

[kchen]

From: David Miller <davem@davemloft.net>
Date: Mon, 07 Jan 2019 09:10:31 -0800

 > From: David Miller <davem@davemloft.net>
 >
> From: kchen <kchen@synology.com>
> Date: Sun,  6 Jan 2019 11:28:13 +0800
> 
>> From: JianJhen Chen <kchen@synology.com>
>>
>> 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>
> 
> Indeed, this looks correct.
> 
> Applied and queued up for -stable, thanks.
> 

Thank you for the confirmation.