Commit 05dd04b2 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

inetpeer: avoid false sharing in inet_peer_xrlim_allow() 



Under DOS, inet_peer_xrlim_allow() might be called millions
of times per second from different cpus.

Make sure to write over peer->rate_tokens and peer->rate_last
only when really needed.

Note the inherent races of this function are still there,
we do not care of precise ICMP rate limiting.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarWillem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20241219150330.3159027-1-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 710aebda

net/ipv4/inetpeer.c

+11 −7
Original line number Diff line number Diff line
@@ -246,23 +246,27 @@ void inet_putpeer(struct inet_peer *p) 
#define XRLIM_BURST_FACTOR 6

bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)

{

	unsigned long now, token;

	unsigned long now, token, otoken, delta;

	bool rc = false;



	if (!peer)

		return true;



	token = peer->rate_tokens;

	token = otoken = READ_ONCE(peer->rate_tokens);

	now = jiffies;

	token += now - peer->rate_last;

	peer->rate_last = now;

	delta = now - READ_ONCE(peer->rate_last);

	if (delta) {

		WRITE_ONCE(peer->rate_last, now);

		token += delta;

		if (token > XRLIM_BURST_FACTOR * timeout)

			token = XRLIM_BURST_FACTOR * timeout;

	}

	if (token >= timeout) {

		token -= timeout;

		rc = true;

	}

	peer->rate_tokens = token;

	if (token != otoken)

		WRITE_ONCE(peer->rate_tokens, token);

	return rc;

}

EXPORT_SYMBOL(inet_peer_xrlim_allow);