The branch main has been updated by tuexen: URL: https://cgit.FreeBSD.org/src/commit/?id=c2900b6e8255ba4f54dbd897cf42427db577ed3d
commit c2900b6e8255ba4f54dbd897cf42427db577ed3d Author: Michael Tuexen <[email protected]> AuthorDate: 2025-09-30 20:06:33 +0000 Commit: Michael Tuexen <[email protected]> CommitDate: 2025-09-30 20:06:33 +0000 tcp: apply rate limits to challenge ACKs When sending challenge ACKs from the SYN-cache, apply the same rate limiting as in other states. Reviewed by: cc, rrs MFC after: 3 days Sponsored by: Netflix, Inc. Differential Revision: https://reviews.freebsd.org/D52754 --- sys/netinet/tcp_syncache.c | 28 ++++++++++++++++++++++++---- sys/netinet/tcp_syncache.h | 2 ++ 2 files changed, 26 insertions(+), 4 deletions(-) diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c index 1ee6c6e31f33..72e9dccea9a5 100644 --- a/sys/netinet/tcp_syncache.c +++ b/sys/netinet/tcp_syncache.c @@ -122,6 +122,7 @@ static void syncache_drop(struct syncache *, struct syncache_head *); static void syncache_free(struct syncache *); static void syncache_insert(struct syncache *, struct syncache_head *); static int syncache_respond(struct syncache *, const struct mbuf *, int); +static int syncache_send_challenge_ack(struct syncache *, struct mbuf *); static struct socket *syncache_socket(struct syncache *, struct socket *, struct mbuf *m); static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, @@ -694,10 +695,7 @@ syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th, struct mbuf *m, "sending challenge ACK\n", s, __func__, th->th_seq, sc->sc_irs + 1, sc->sc_wnd); - if (syncache_respond(sc, m, TH_ACK) == 0) { - TCPSTAT_INC(tcps_sndacks); - TCPSTAT_INC(tcps_sndtotal); - } else { + if (syncache_send_challenge_ack(sc, m) != 0) { syncache_drop(sc, sch); TCPSTAT_INC(tcps_sc_dropped); } @@ -963,6 +961,10 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) if (sc->sc_rxmits > 1) tp->snd_cwnd = 1; + /* Copy over the challenge ACK state. */ + tp->t_challenge_ack_end = sc->sc_challenge_ack_end; + tp->t_challenge_ack_cnt = sc->sc_challenge_ack_cnt; + #ifdef TCP_OFFLOAD /* * Allow a TOE driver to install its hooks. Note that we hold the @@ -2053,6 +2055,24 @@ syncache_respond(struct syncache *sc, const struct mbuf *m0, int flags) return (error); } +static int +syncache_send_challenge_ack(struct syncache *sc, struct mbuf *m) +{ + int error; + + if (tcp_challenge_ack_check(&sc->sc_challenge_ack_end, + &sc->sc_challenge_ack_cnt)) { + error = syncache_respond(sc, m, TH_ACK); + if (error == 0) { + TCPSTAT_INC(tcps_sndacks); + TCPSTAT_INC(tcps_sndtotal); + } + } else { + error = 0; + } + return (error); +} + /* * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks * that exceed the capacity of the syncache by avoiding the storage of any diff --git a/sys/netinet/tcp_syncache.h b/sys/netinet/tcp_syncache.h index a336571f12c9..37f6ff3d6ca9 100644 --- a/sys/netinet/tcp_syncache.h +++ b/sys/netinet/tcp_syncache.h @@ -67,6 +67,8 @@ struct syncache { u_int8_t sc_requested_s_scale:4, sc_requested_r_scale:4; u_int16_t sc_flags; + u_int32_t sc_challenge_ack_cnt; /* chall. ACKs sent in epoch */ + sbintime_t sc_challenge_ack_end; /* End of chall. ack epoch */ #if defined(TCP_OFFLOAD) struct toedev *sc_tod; /* entry added by this TOE */ void *sc_todctx; /* TOE driver context */
