Commit e7d0c885 authored by Stephen Hemminger's avatar Stephen Hemminger Committed by David S. Miller
Browse files

[TCP]: cubic - eliminate use of receive time stamp 



Remove use of received timestamp option value from RTT calculation in Cubic.
A hostile receiver may be returning a larger timestamp option than the original
value. This would cause the sender to believe the malevolent receiver had
a larger RTT and because Cubic tries to provide some RTT friendliness, the
sender would then favor the liar.

Instead, use the jiffie resolutionRTT value already computed and
passed back after ack.

Signed-off-by: default avatarStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 30cfd0ba

net/ipv4/tcp_cubic.c

+18 −28
Original line number Diff line number Diff line
@@ -246,38 +246,12 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 
		ca->cnt = 1;

}





/* Keep track of minimum rtt */

static inline void measure_delay(struct sock *sk)

{

	const struct tcp_sock *tp = tcp_sk(sk);

	struct bictcp *ca = inet_csk_ca(sk);

	u32 delay;



	/* No time stamp */

	if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||

	     /* Discard delay samples right after fast recovery */

	    (s32)(tcp_time_stamp - ca->epoch_start) < HZ)

		return;



	delay = (tcp_time_stamp - tp->rx_opt.rcv_tsecr)<<3;

	if (delay == 0)

		delay = 1;



	/* first time call or link delay decreases */

	if (ca->delay_min == 0 || ca->delay_min > delay)

		ca->delay_min = delay;

}



static void bictcp_cong_avoid(struct sock *sk, u32 ack,

			      u32 in_flight, int data_acked)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct bictcp *ca = inet_csk_ca(sk);



	if (data_acked)

		measure_delay(sk);



	if (!tcp_is_cwnd_limited(sk, in_flight))

		return;
@@ -337,14 +311,30 @@ static void bictcp_state(struct sock *sk, u8 new_state) 
static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)

{

	const struct inet_connection_sock *icsk = inet_csk(sk);

	struct bictcp *ca = inet_csk_ca(sk);

	u32 delay;



	if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {

		struct bictcp *ca = inet_csk_ca(sk);

		cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;

		ca->delayed_ack += cnt;

	}

}



	/* Some calls are for duplicates without timetamps */

	if (rtt_us < 0)

		return;



	/* Discard delay samples right after fast recovery */

	if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)

		return;



	delay = usecs_to_jiffies(rtt_us) << 3;

	if (delay == 0)

		delay = 1;



	/* first time call or link delay decreases */

	if (ca->delay_min == 0 || ca->delay_min > delay)

		ca->delay_min = delay;

}



static struct tcp_congestion_ops cubictcp = {

	.init		= bictcp_init,

CRA Git | Maintained and supported by SUSTech CRA and CCSE