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    Subject[PATCH 4.4 06/32] neighbour: Disregard DEAD dst in neigh_update
    Date
    From: Tong Zhu <zhutong@amazon.com>

    [ 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>
    ---
    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 40d33431bc58..17997902d316 100644
    --- a/net/core/neighbour.c
    +++ b/net/core/neighbour.c
    @@ -1234,7 +1234,7 @@ 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;
    --
    2.30.2


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