Date: Thu, 25 Jul 2024 20:57:13 GMT From: Michael Tuexen <tuexen@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 40299c55a05f - main - tcp: implement challenge ACK throttling for the base stack Message-ID: <202407252057.46PKvD5J077768@gitrepo.freebsd.org>
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The branch main has been updated by tuexen: URL: https://cgit.FreeBSD.org/src/commit/?id=40299c55a05ff008102e24269d5f2d7fa7b6842d commit 40299c55a05ff008102e24269d5f2d7fa7b6842d Author: Michael Tuexen <tuexen@FreeBSD.org> AuthorDate: 2024-07-25 11:54:52 +0000 Commit: Michael Tuexen <tuexen@FreeBSD.org> CommitDate: 2024-07-25 11:54:52 +0000 tcp: implement challenge ACK throttling for the base stack Implement ACK throttling of challenge ACKs as described in RFC 5961. Reviewed by: Peter Lei, rscheff, cc MFC after: 1 week Sponsored by: Netflix, Inc. Differential Revision: https://reviews.freebsd.org/D46066 --- sys/netinet/tcp_input.c | 15 +++------------ sys/netinet/tcp_subr.c | 39 +++++++++++++++++++++++++++++++++++++++ sys/netinet/tcp_var.h | 6 ++++++ 3 files changed, 48 insertions(+), 12 deletions(-) diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c index ad17a9fdfb93..b64a71837ab4 100644 --- a/sys/netinet/tcp_input.c +++ b/sys/netinet/tcp_input.c @@ -2208,10 +2208,7 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th, } } else { TCPSTAT_INC(tcps_badrst); - /* Send challenge ACK. */ - tcp_respond(tp, mtod(m, void *), th, m, - tp->rcv_nxt, tp->snd_nxt, TH_ACK); - tp->last_ack_sent = tp->rcv_nxt; + tcp_send_challenge_ack(tp, th, m); m = NULL; } } @@ -2233,10 +2230,7 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th, rstreason = BANDLIM_UNLIMITED; } else { tcp_ecn_input_syn_sent(tp, thflags, iptos); - /* Send challenge ACK. */ - tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt, - tp->snd_nxt, TH_ACK); - tp->last_ack_sent = tp->rcv_nxt; + tcp_send_challenge_ack(tp, th, m); m = NULL; } goto drop; @@ -2474,10 +2468,7 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th, TCPSTAT_INC(tcps_rcvghostack); else TCPSTAT_INC(tcps_rcvacktooold); - /* Send a challenge ACK. */ - tcp_respond(tp, mtod(m, void *), th, m, - tp->rcv_nxt, tp->snd_nxt, TH_ACK); - tp->last_ack_sent = tp->rcv_nxt; + tcp_send_challenge_ack(tp, th, m); m = NULL; goto drop; } diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c index 42d29d64e09f..0665564955d2 100644 --- a/sys/netinet/tcp_subr.c +++ b/sys/netinet/tcp_subr.c @@ -2181,6 +2181,45 @@ tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m, lgb->tlb_errno = output_ret; } +/* + * Send a challenge ack (no data, no SACK option), but not more than + * tcp_ack_war_cnt per tcp_ack_war_time_window (per TCP connection). + */ +void +tcp_send_challenge_ack(struct tcpcb *tp, struct tcphdr *th, struct mbuf *m) +{ + sbintime_t now; + bool send_challenge_ack; + + if (tcp_ack_war_time_window == 0 || tcp_ack_war_cnt == 0) { + /* ACK war protection is disabled. */ + send_challenge_ack = true; + } else { + /* Start new epoch, if the previous one is already over. */ + now = getsbinuptime(); + if (tp->t_challenge_ack_end < now) { + tp->t_challenge_ack_cnt = 0; + tp->t_challenge_ack_end = now + + tcp_ack_war_time_window * SBT_1MS; + } + /* + * Send a challenge ACK, if less than tcp_ack_war_cnt have been + * sent in the current epoch. + */ + if (tp->t_challenge_ack_cnt < tcp_ack_war_cnt) { + send_challenge_ack = true; + tp->t_challenge_ack_cnt++; + } else { + send_challenge_ack = false; + } + } + if (send_challenge_ack) { + tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt, + tp->snd_nxt, TH_ACK); + tp->last_ack_sent = tp->rcv_nxt; + } +} + /* * Create a new TCP control block, making an empty reassembly queue and hooking * it to the argument protocol control block. The `inp' parameter must have diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h index c06efa601a81..af82d0bfeaaa 100644 --- a/sys/netinet/tcp_var.h +++ b/sys/netinet/tcp_var.h @@ -465,6 +465,11 @@ struct tcpcb { /* TCP Fast Open */ uint8_t t_tfo_client_cookie_len; /* TFO client cookie length */ uint32_t t_end_info_status; /* Status flag of end info */ + sbintime_t t_challenge_ack_end; /* End of the challenge ack epoch */ + uint32_t t_challenge_ack_cnt; /* Number of challenge ACKs sent in + * current epoch + */ + unsigned int *t_tfo_pending; /* TFO server pending counter */ union { uint8_t client[TCP_FASTOPEN_MAX_COOKIE_LEN]; @@ -1460,6 +1465,7 @@ int tcp_default_output(struct tcpcb *); void tcp_state_change(struct tcpcb *, int); void tcp_respond(struct tcpcb *, void *, struct tcphdr *, struct mbuf *, tcp_seq, tcp_seq, uint16_t); +void tcp_send_challenge_ack(struct tcpcb *, struct tcphdr *, struct mbuf *); bool tcp_twcheck(struct inpcb *, struct tcpopt *, struct tcphdr *, struct mbuf *, int); void tcp_setpersist(struct tcpcb *);
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