From: Tong Zhu zhutong@amazon.com

stable inclusion from linux-4.19.189 commit d8a841f43677e74d64c46a025eb095ec590c22ce

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[ Upstream commit d47ec7a0a7271dda08932d6208e4ab65ab0c987c ]

After a short network outage, the dst_entry is timed out and put in DST_OBSOLETE_DEAD. We are in this code because arp reply comes from this neighbour after network recovers. There is a potential race condition that dst_entry is still in DST_OBSOLETE_DEAD. With that, another neighbour lookup causes more harm than good.

In best case all packets in arp_queue are lost. This is counterproductive to the original goal of finding a better path for those packets.

I observed a worst case with 4.x kernel where a dst_entry in DST_OBSOLETE_DEAD state is associated with loopback net_device. It leads to an ethernet header with all zero addresses. A packet with all zero source MAC address is quite deadly with mac80211, ath9k and 802.11 block ack. It fails ieee80211_find_sta_by_ifaddr in ath9k (xmit.c). Ath9k flushes tx queue (ath_tx_complete_aggr). BAW (block ack window) is not updated. BAW logic is damaged and ath9k transmission is disabled.

Signed-off-by: Tong Zhu zhutong@amazon.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Yang Yingliang yangyingliang@huawei.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 6e890f51b7d86..e471c32e448f6 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;