| Message ID | 41B57547-A148-49D5-8F03-18F976263CED@netapp.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
From: "Cui, Cheng" <Cheng.Cui@netapp.com> Date: Tue, 14 Feb 2017 23:14:59 +0000 > This updates tcp_acceptable_seq(), one of the oldest functions since 2.4.0, by > preventing sending out a left-shifted sequence number from a Linux sender in > response to a peer's shrunk receive-window caused by losing least significant > bits in window-scaling. > > RFC7323 page 10 (Chapter 2.4. Addressing Window Retraction) specifies sender > side responsibility to handle the sequence number out of window: >> On the sender side: >> >> 3) The initial transmission MUST be within the window announced by >> the most recent <ACK>. > > Some related discussion can be found at the IETF [tcpm] mailing list: > https://mailarchive.ietf.org/arch/msg/tcpm/pPO7cYxtky27Qto9b30eaHB_RQI > > The issue has been reproduced and the patch has been verified by scp a 20GB file > from a Linux box using kernel version 4.4.48 to a FreeBSD 11.0 box. > > [ I mainly want feedback to see if everyone is OK with the approach. ] > > Cc: "David S. Miller" <davem@davemloft.net> > Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> > Cc: James Morris <jmorris@namei.org> > Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org> > Cc: Patrick McHardy <kaber@trash.net> > Signed-off-by: Cheng Cui <Cheng.Cui@netapp.com> Patch looks fine to me, but too much parenthesis in the initial conditional and it's easier to see to high level structure if you format the check like this; if (!before(tcp_wnd_end(tp), tp->snd_nxt) || (tp->rx_opt.wscale_ok && ((tp->snd_nxt - tcp_wnd_end(tp)) < (1 << tp->rx_opt.rcv_wscale)))) THanks.
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 1d5331a..29d736d 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -85,7 +85,8 @@ static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb) tcp_skb_pcount(skb)); } -/* SND.NXT, if window was not shrunk. +/* SND.NXT, if window was not shrunk or the amount of shrunk was less than one + * window scaling factor due to loss of precision. * If window has been shrunk, what should we make? It is not clear at all. * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-( * Anything in between SND.UNA...SND.UNA+SND.WND also can be already @@ -95,7 +96,8 @@ static inline __u32 tcp_acceptable_seq(const struct sock *sk) { const struct tcp_sock *tp = tcp_sk(sk); - if (!before(tcp_wnd_end(tp), tp->snd_nxt)) + if ((!before(tcp_wnd_end(tp), tp->snd_nxt)) || (tp->rx_opt.wscale_ok && + ((tp->snd_nxt - tcp_wnd_end(tp)) < (1 << tp->rx_opt.rcv_wscale)))) return tp->snd_nxt; else return tcp_wnd_end(tp);