From: Tong Zhu <zhutong@amazon.com>
To: <davem@davemloft.net>, <kuba@kernel.org>, <kvalo@codeaurora.org>,
<johannes@sipsolutions.net>, <netdev@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Cc: <zhutong@amazon.com>
Subject: [PATCH] neighbour: Disregard DEAD dst in neigh_update
Date: Fri, 19 Mar 2021 14:33:37 -0400 [thread overview]
Message-ID: <20210319183327.GA25778@ucf43ac461c9a53.ant.amazon.com> (raw)
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>
---
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 e2982b3970b8..8379719d1dce 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1379,7 +1379,7 @@ static int __neigh_update(struct neighbour *neigh, const u8 *lladdr,
* 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
next reply other threads:[~2021-03-19 18:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-19 18:33 Tong Zhu [this message]
-- strict thread matches above, loose matches on Subject: below --
2020-12-30 22:54 [PATCH] neighbour: Disregard DEAD dst in neigh_update Tong Zhu
2021-01-06 0:05 ` David Miller
2021-01-08 2:36 ` Your Real Name
2021-01-08 7:34 ` Greg KH
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