netdev - [PATCH net-next v2 1/2] tcp: ensure to use the most recently sent skb when filling the rate sample

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 16 Apr 2022 17:19:08 +0800
From:   Pengcheng Yang <yangpc@...gsu.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Pengcheng Yang <yangpc@...gsu.com>
Subject: [PATCH net-next v2 1/2] tcp: ensure to use the most recently sent skb when filling the rate sample

If an ACK (s)acks multiple skbs, we favor the information
from the most recently sent skb by choosing the skb with
the highest prior_delivered count. But in the interval
between receiving ACKs, we send multiple skbs with the same
prior_delivered, because the tp->delivered only changes
when we receive an ACK.

We used RACK's solution, copying tcp_rack_sent_after() as
tcp_skb_sent_after() helper to determine "which packet was
sent last?". Later, we will use tcp_skb_sent_after() instead
in RACK.

Signed-off-by: Pengcheng Yang <yangpc@...gsu.com>
Cc: Neal Cardwell <ncardwell@...gle.com>
---
 include/net/tcp.h   |  6 ++++++
 net/ipv4/tcp_rate.c | 11 ++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6d50a66..fcd69fc 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1042,6 +1042,7 @@ struct rate_sample {
 	int  losses;		/* number of packets marked lost upon ACK */
 	u32  acked_sacked;	/* number of packets newly (S)ACKed upon ACK */
 	u32  prior_in_flight;	/* in flight before this ACK */
+	u32  last_end_seq;	/* end_seq of most recently ACKed packet */
 	bool is_app_limited;	/* is sample from packet with bubble in pipe? */
 	bool is_retrans;	/* is sample from retransmission? */
 	bool is_ack_delayed;	/* is this (likely) a delayed ACK? */
@@ -1158,6 +1159,11 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
 		  bool is_sack_reneg, struct rate_sample *rs);
 void tcp_rate_check_app_limited(struct sock *sk);
 
+static inline bool tcp_skb_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2)
+{
+	return t1 > t2 || (t1 == t2 && after(seq1, seq2));
+}
+
 /* These functions determine how the current flow behaves in respect of SACK
  * handling. SACK is negotiated with the peer, and therefore it can vary
  * between different flows.
diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index 617b818..a8f6d9d 100644
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -74,27 +74,32 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
  *
  * If an ACK (s)acks multiple skbs (e.g., stretched-acks), this function is
  * called multiple times. We favor the information from the most recently
- * sent skb, i.e., the skb with the highest prior_delivered count.
+ * sent skb, i.e., the skb with the most recently sent time and the highest
+ * sequence.
  */
 void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
 			    struct rate_sample *rs)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+	u64 tx_tstamp;
 
 	if (!scb->tx.delivered_mstamp)
 		return;
 
+	tx_tstamp = tcp_skb_timestamp_us(skb);
 	if (!rs->prior_delivered ||
-	    after(scb->tx.delivered, rs->prior_delivered)) {
+	    tcp_skb_sent_after(tx_tstamp, tp->first_tx_mstamp,
+			       scb->end_seq, rs->last_end_seq)) {
 		rs->prior_delivered_ce  = scb->tx.delivered_ce;
 		rs->prior_delivered  = scb->tx.delivered;
 		rs->prior_mstamp     = scb->tx.delivered_mstamp;
 		rs->is_app_limited   = scb->tx.is_app_limited;
 		rs->is_retrans	     = scb->sacked & TCPCB_RETRANS;
+		rs->last_end_seq     = scb->end_seq;
 
 		/* Record send time of most recently ACKed packet: */
-		tp->first_tx_mstamp  = tcp_skb_timestamp_us(skb);
+		tp->first_tx_mstamp  = tx_tstamp;
 		/* Find the duration of the "send phase" of this window: */
 		rs->interval_us = tcp_stamp_us_delta(tp->first_tx_mstamp,
 						     scb->tx.first_tx_mstamp);
-- 
1.8.3.1