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Date:   Wed, 30 Dec 2020 17:54:23 -0500
From:   Tong Zhu <zhutong@amazon.com>
To:     <davem@davemloft.net>, <sashal@kernel.org>, <edumazet@google.com>,
        <zhutong@amazon.com>, <vvs@virtuozzo.com>
CC:     <netdev@vger.kernel.org>, <stable@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: [PATCH] neighbour: Disregard DEAD dst in neigh_update
Message-ID: <20201230225415.GA490@ucf43ac461c9a53.ant.amazon.com>
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User-Agent: Mutt/1.9.4 (2018-02-28)
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In 4.x kernel a dst in DST_OBSOLETE_DEAD state is associated
with loopback net_device and leads to loopback neighbour. It
leads to an ethernet header with all zero addresses.

A very troubling case is working with mac80211 and ath9k.
A packet with all zero source MAC address to mac80211 will
eventually fail ieee80211_find_sta_by_ifaddr in ath9k (xmit.c).
As result, ath9k flushes tx queue (ath_tx_complete_aggr) without
updating baw (block ack window), damages baw logic and disables
transmission.

Signed-off-by: Tong Zhu <zhutong@amazon.com>
---
 net/core/neighbour.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 6e890f51b7d8..e471c32e448f 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1271,7 +1271,7 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
 			 * we can reinject the packet there.
 			 */
 			n2 = NULL;
-			if (dst) {
+			if (dst && dst->obsolete != DST_OBSOLETE_DEAD) {
 				n2 = dst_neigh_lookup_skb(dst, skb);
 				if (n2)
 					n1 = n2;
-- 
2.17.1