Commit 8d23e166 authored May 13, 2021 by Tao Liu Committed by Greg Kroah-Hartman Jun 03, 2021

openvswitch: meter: fix race when getting now_ms.

[ Upstream commit e4df1b0c24350a0f00229ff895a91f1072bd850d ]

We have observed meters working unexpected if traffic is 3+Gbit/s
with multiple connections.

now_ms is not pretected by meter->lock, we may get a negative
long_delta_ms when another cpu updated meter->used, then:
    delta_ms = (u32)long_delta_ms;
which will be a large value.

    band->bucket += delta_ms * band->rate;
then we get a wrong band->bucket.

OpenVswitch userspace datapath has fixed the same issue[1] some
time ago, and we port the implementation to kernel datapath.

[1] https://patchwork.ozlabs.org/project/openvswitch/patch/20191025114436.9746-1-i.maximets@ovn.org/



Fixes: 96fbc13d ("openvswitch: Add meter infrastructure")
Signed-off-by: Tao Liu <thomas.liu@ucloud.cn>
Suggested-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent e1c38c2f

net/openvswitch/meter.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -464,6 +464,14 @@ bool ovs_meter_execute(struct datapath dp, struct sk_buff skb,
		spin_lock(&meter->lock);

		long_delta_ms = (now_ms - meter->used); /* ms */
		if (long_delta_ms < 0) {
		/* This condition means that we have several threads fighting
		* for a meter lock, and the one who received the packets a
		* bit later wins. Assuming that all racing threads received
		* packets at the same time to avoid overflow.
		*/
		long_delta_ms = 0;
		}

		/* Make sure delta_ms will not be too large, so that bucket will not
		* wrap around below.