Date: Wed, 9 Jun 2021 00:20:47 GMT From: Michael Tuexen <tuexen@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: fc53b7269fed - stable/13 - tcp: A better fix for the previously attempted fix of the ack-war issue with tcp. Message-ID: <202106090020.1590KlIb082545@gitrepo.freebsd.org>
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The branch stable/13 has been updated by tuexen: URL: https://cgit.FreeBSD.org/src/commit/?id=fc53b7269fedf53b5fb13e4587d017d6bd833cf3 commit fc53b7269fedf53b5fb13e4587d017d6bd833cf3 Author: Randall Stewart <rrs@FreeBSD.org> AuthorDate: 2021-06-04 09:26:43 +0000 Commit: Michael Tuexen <tuexen@FreeBSD.org> CommitDate: 2021-06-09 00:19:47 +0000 tcp: A better fix for the previously attempted fix of the ack-war issue with tcp. So it turns out that my fix before was not correct. It ended with us failing some of the "improved" SYN tests, since we are not in the correct states. With more digging I have figured out the root of the problem is that when we receive a SYN|FIN the reassembly code made it so we create a segq entry to hold the FIN. In the established state where we were not in order this would be correct i.e. a 0 len with a FIN would need to be accepted. But if you are in a front state we need to strip the FIN so we correctly handle the ACK but ignore the FIN. This gets us into the proper states and avoids the previous ack war. I back out some of the previous changes but then add a new change here in tcp_reass() that fixes the root cause of the issue. We still leave the rack panic fixes in place however. Reviewed by: mtuexen Sponsored by: Netflix Inc Differential Revision: https://reviews.freebsd.org/D30627 (cherry picked from commit 4747500deaaa7765ba1c0413197c23ddba4faf49) --- sys/netinet/tcp_input.c | 12 +++--------- sys/netinet/tcp_reass.c | 14 ++++++++++++++ sys/netinet/tcp_stacks/bbr.c | 12 +++--------- sys/netinet/tcp_stacks/rack.c | 13 ++++--------- sys/netinet/tcp_usrreq.c | 16 ---------------- 5 files changed, 24 insertions(+), 43 deletions(-) diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c index b6a198b49eef..5e25b38c45e2 100644 --- a/sys/netinet/tcp_input.c +++ b/sys/netinet/tcp_input.c @@ -3184,15 +3184,9 @@ dodata: /* XXX */ * when trimming from the head. */ tcp_seq temp = save_start; - if (tlen || (th->th_seq != tp->rcv_nxt)) { - /* - * We add the th_seq != rcv_nxt to - * catch the case of a stand alone out - * of order FIN. - */ - thflags = tcp_reass(tp, th, &temp, &tlen, m); - tp->t_flags |= TF_ACKNOW; - } + + thflags = tcp_reass(tp, th, &temp, &tlen, m); + tp->t_flags |= TF_ACKNOW; } if ((tp->t_flags & TF_SACK_PERMIT) && (save_tlen > 0) && diff --git a/sys/netinet/tcp_reass.c b/sys/netinet/tcp_reass.c index 310d7d540507..e708b6db14c0 100644 --- a/sys/netinet/tcp_reass.c +++ b/sys/netinet/tcp_reass.c @@ -571,6 +571,7 @@ tcp_reass(struct tcpcb *tp, struct tcphdr *th, tcp_seq *seq_start, * the rcv_nxt <-> rcv_wnd but thats * already done for us by the caller. */ +strip_fin: #ifdef TCP_REASS_COUNTERS counter_u64_add(tcp_zero_input, 1); #endif @@ -579,6 +580,19 @@ tcp_reass(struct tcpcb *tp, struct tcphdr *th, tcp_seq *seq_start, tcp_reass_log_dump(tp); #endif return (0); + } else if ((*tlenp == 0) && + (th->th_flags & TH_FIN) && + !TCPS_HAVEESTABLISHED(tp->t_state)) { + /* + * We have not established, and we + * have a FIN and no data. Lets treat + * this as the same as if the FIN were + * not present. We don't want to save + * the FIN bit in a reassembly buffer + * we want to get established first before + * we do that (the peer will retransmit). + */ + goto strip_fin; } /* * Will it fit? diff --git a/sys/netinet/tcp_stacks/bbr.c b/sys/netinet/tcp_stacks/bbr.c index a10235f94c89..a3f7961af345 100644 --- a/sys/netinet/tcp_stacks/bbr.c +++ b/sys/netinet/tcp_stacks/bbr.c @@ -8321,15 +8321,9 @@ bbr_process_data(struct mbuf *m, struct tcphdr *th, struct socket *so, * trimming from the head. */ tcp_seq temp = save_start; - if (tlen || (th->th_seq != tp->rcv_nxt)) { - /* - * We add the th_seq != rcv_nxt to - * catch the case of a stand alone out - * of order FIN. - */ - thflags = tcp_reass(tp, th, &temp, &tlen, m); - tp->t_flags |= TF_ACKNOW; - } + + thflags = tcp_reass(tp, th, &temp, &tlen, m); + tp->t_flags |= TF_ACKNOW; } if ((tp->t_flags & TF_SACK_PERMIT) && (save_tlen > 0) && diff --git a/sys/netinet/tcp_stacks/rack.c b/sys/netinet/tcp_stacks/rack.c index 63574691112c..4a547e900c4f 100644 --- a/sys/netinet/tcp_stacks/rack.c +++ b/sys/netinet/tcp_stacks/rack.c @@ -10236,15 +10236,10 @@ rack_process_data(struct mbuf *m, struct tcphdr *th, struct socket *so, * trimming from the head. */ tcp_seq temp = save_start; - if (tlen || (th->th_seq != tp->rcv_nxt)) { - /* - * We add the th_seq != rcv_nxt to - * catch the case of a stand alone out - * of order FIN. - */ - thflags = tcp_reass(tp, th, &temp, &tlen, m); - tp->t_flags |= TF_ACKNOW; - } + + thflags = tcp_reass(tp, th, &temp, &tlen, m); + tp->t_flags |= TF_ACKNOW; + } if ((tp->t_flags & TF_SACK_PERMIT) && (save_tlen > 0) && diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c index 55aa609fd084..bd847426681e 100644 --- a/sys/netinet/tcp_usrreq.c +++ b/sys/netinet/tcp_usrreq.c @@ -2635,22 +2635,6 @@ tcp_usrclosed(struct tcpcb *tp) tcp_state_change(tp, TCPS_LAST_ACK); break; } - if ((tp->t_state == TCPS_LAST_ACK) && - (tp->t_flags & TF_SENTFIN)) { - /* - * If we have reached LAST_ACK, and - * we sent a FIN (e.g. via MSG_EOR), then - * we really should move to either FIN_WAIT_1 - * or FIN_WAIT_2 depending on snd_max/snd_una. - */ - if (tp->snd_una == tp->snd_max) { - /* The FIN is acked */ - tcp_state_change(tp, TCPS_FIN_WAIT_2); - } else { - /* The FIN is still outstanding */ - tcp_state_change(tp, TCPS_FIN_WAIT_1); - } - } if (tp->t_state >= TCPS_FIN_WAIT_2) { soisdisconnected(tp->t_inpcb->inp_socket); /* Prevent the connection hanging in FIN_WAIT_2 forever. */
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