Messages in this thread | | | From | Zhouyi Zhou <> | Date | Sat, 19 Mar 2022 19:34:40 +0800 | Subject | Re: [PATCH v2] net:ipv4: send an ack when seg.ack > snd.nxt |
| |
Thanks for reviewing my patch
On Sat, Mar 19, 2022 at 7:14 PM Eric Dumazet <edumazet@google.com> wrote: > > On Sat, Mar 19, 2022 at 4:04 AM <zhouzhouyi@gmail.com> wrote: > > > > From: Zhouyi Zhou <zhouzhouyi@gmail.com> > > > > In RFC 793, page 72: "If the ACK acks something not yet sent > > (SEG.ACK > SND.NXT) then send an ACK, drop the segment, > > and return." > > > > Fix Linux's behavior according to RFC 793. > > > > Reported-by: Wei Xu <xuweihf@ustc.edu.cn> > > Signed-off-by: Wei Xu <xuweihf@ustc.edu.cn> > > Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com> > > --- > > Thank Florian Westphal for pointing out > > the potential duplicated ack bug in patch version 1. > > I am travelling this week, but I think your patch is not necessary and > might actually be bad. > > Please provide more details of why nobody complained of this until today. > > Also I doubt you actually fully tested this patch, sending a V2 30 > minutes after V1. > > If yes, please provide a packetdrill test. I am a beginner to TCP, although I have submitted once a patch to netdev in 2013 (aaa0c23cb90141309f5076ba5e3bfbd39544b985), this is first time I learned packetdrill test. I think I should do the packetdrill test in the coming days, and provide more details of how this (RFC793 related) can happen.
Apologize sincerely in advance if I have made noise.
Thank you for your time
Sincerely Zhouyi > > Thank you. > > > -- > > net/ipv4/tcp_input.c | 21 +++++++++++++-------- > > 1 file changed, 13 insertions(+), 8 deletions(-) > > > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > > index bfe4112e000c..4bbf85d7ea8c 100644 > > --- a/net/ipv4/tcp_input.c > > +++ b/net/ipv4/tcp_input.c > > @@ -3771,11 +3771,13 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) > > goto old_ack; > > } > > > > - /* If the ack includes data we haven't sent yet, discard > > - * this segment (RFC793 Section 3.9). > > + /* If the ack includes data we haven't sent yet, then send > > + * an ack, drop this segment, and return (RFC793 Section 3.9 page 72). > > */ > > - if (after(ack, tp->snd_nxt)) > > - return -1; > > + if (after(ack, tp->snd_nxt)) { > > + tcp_send_ack(sk); > > + return -2; > > + } > > > > if (after(ack, prior_snd_una)) { > > flag |= FLAG_SND_UNA_ADVANCED; > > @@ -6385,6 +6387,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb) > > struct request_sock *req; > > int queued = 0; > > bool acceptable; > > + int ret; > > > > switch (sk->sk_state) { > > case TCP_CLOSE: > > @@ -6451,14 +6454,16 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb) > > return 0; > > > > /* step 5: check the ACK field */ > > - acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH | > > - FLAG_UPDATE_TS_RECENT | > > - FLAG_NO_CHALLENGE_ACK) > 0; > > + ret = tcp_ack(sk, skb, FLAG_SLOWPATH | > > + FLAG_UPDATE_TS_RECENT | > > + FLAG_NO_CHALLENGE_ACK); > > + acceptable = ret > 0; > > > > if (!acceptable) { > > if (sk->sk_state == TCP_SYN_RECV) > > return 1; /* send one RST */ > > - tcp_send_challenge_ack(sk); > > + if (ret > -2) > > + tcp_send_challenge_ack(sk); > > goto discard; > > } > > switch (sk->sk_state) { > > -- > > 2.25.1 > >
| |