net, neigh: Set lower cap for neigh_managed_work rearming

Yuwei reported that plain reuse of DELAY_PROBE_TIME to rearm work queue
in neigh_managed_work is problematic if user explicitly configures the
DELAY_PROBE_TIME to 0 for a neighbor table. Such misconfig can then hog
CPU to 100% processing the system work queue. Instead, set lower interval
bound to HZ which is totally sufficient. Yuwei is additionally looking
into making the interval separately configurable from DELAY_PROBE_TIME.

Reported-by: Yuwei Wang <wangyuweihx@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/netdev/797c3c53-ce1b-9f60-e253-cda615788f4a@iogearbox.net
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/3b8c5aa906c52c3a8c995d1b2e8ccf650ea7c716.1653432794.git.daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 47b6c1f..5462528 100644 (file)
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1579,7 +1579,7 @@ static void neigh_managed_work(struct work_struct *work)
        list_for_each_entry(neigh, &tbl->managed_list, managed_list)
                neigh_event_send_probe(neigh, NULL, false);
        queue_delayed_work(system_power_efficient_wq, &tbl->managed_work,
-                          NEIGH_VAR(&tbl->parms, DELAY_PROBE_TIME));
+                          max(NEIGH_VAR(&tbl->parms, DELAY_PROBE_TIME), HZ));
        write_unlock_bh(&tbl->lock);
 }