Messages in this thread | | | From | Eric Dumazet <> | Date | Sat, 19 Mar 2022 04:14:43 -0700 | Subject | Re: [PATCH v2] net:ipv4: send an ack when seg.ack > snd.nxt |
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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.
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 >
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