netdev - Re: [PATCH nf] netfilter: set default timeout to 3 secs for sctp shutdown send and recv state

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Date: Tue, 15 Aug 2023 10:01:41 -0400
From: Xin Long <lucien.xin@...il.com>
To: Sriram Yagnaraman <sriram.yagnaraman@....tech>
Cc: network dev <netdev@...r.kernel.org>, 
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>, 
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>, "davem@...emloft.net" <davem@...emloft.net>, 
	"kuba@...nel.org" <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	Pablo Neira Ayuso <pablo@...filter.org>, Jozsef Kadlecsik <kadlec@...filter.org>, 
	Florian Westphal <fw@...len.de>, Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH nf] netfilter: set default timeout to 3 secs for sctp
 shutdown send and recv state

On Tue, Aug 15, 2023 at 3:59 AM Sriram Yagnaraman
<sriram.yagnaraman@....tech> wrote:
>
>
>
> > -----Original Message-----
> > From: Xin Long <lucien.xin@...il.com>
> > Sent: Sunday, 13 August 2023 18:56
> > To: network dev <netdev@...r.kernel.org>; netfilter-devel@...r.kernel.org;
> > linux-sctp@...r.kernel.org
> > Cc: davem@...emloft.net; kuba@...nel.org; Eric Dumazet
> > <edumazet@...gle.com>; Paolo Abeni <pabeni@...hat.com>; Pablo Neira
> > Ayuso <pablo@...filter.org>; Jozsef Kadlecsik <kadlec@...filter.org>; Florian
> > Westphal <fw@...len.de>; Marcelo Ricardo Leitner
> > <marcelo.leitner@...il.com>
> > Subject: [PATCH nf] netfilter: set default timeout to 3 secs for sctp shutdown
> > send and recv state
> >
> > In SCTP protocol, it is using the same timer (T2 timer) for SHUTDOWN and
> > SHUTDOWN_ACK retransmission. However in sctp conntrack the default
> > timeout value for SCTP_CONNTRACK_SHUTDOWN_ACK_SENT state is 3 secs
> > while it's 300 msecs for SCTP_CONNTRACK_SHUTDOWN_SEND/RECV state.
> >
> > As Paolo Valerio noticed, this might cause unwanted expiration of the ct entry.
> > In my test, with 1s tc netem delay set on the NAT path, after the SHUTDOWN is
> > sent, the sctp ct entry enters SCTP_CONNTRACK_SHUTDOWN_SEND state.
> > However, due to 300ms (too short) delay, when the SHUTDOWN_ACK is sent
> > back from the peer, the sctp ct entry has expired and been deleted, and then
> > the SHUTDOWN_ACK has to be dropped.
> >
> > Also, it is confusing these two sysctl options always show 0 due to all timeout
> > values using sec as unit:
> >
> >   net.netfilter.nf_conntrack_sctp_timeout_shutdown_recd = 0
> >   net.netfilter.nf_conntrack_sctp_timeout_shutdown_sent = 0
> >
> > This patch fixes it by also using 3 secs for sctp shutdown send and recv state in
> > sctp conntrack, which is also RTO.initial value in SCTP protocol.
> >
> > Note that the very short time value for
> > SCTP_CONNTRACK_SHUTDOWN_SEND/RECV was probably used for a rare
> > scenario where SHUTDOWN is sent on 1st path but SHUTDOWN_ACK is replied
> > on 2nd path, then a new connection started immediately on 1st path. So this
> > patch also moves from SHUTDOWN_SEND/RECV to CLOSE when receiving INIT
> > in the ORIGINAL direction.
> >
> > Fixes: 9fb9cbb1082d ("[NETFILTER]: Add nf_conntrack subsystem.")
> > Reported-by: Paolo Valerio <pvalerio@...hat.com>
> > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > ---
> >  net/netfilter/nf_conntrack_proto_sctp.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/netfilter/nf_conntrack_proto_sctp.c
> > b/net/netfilter/nf_conntrack_proto_sctp.c
> > index 91eacc9b0b98..b6bcc8f2f46b 100644
> > --- a/net/netfilter/nf_conntrack_proto_sctp.c
> > +++ b/net/netfilter/nf_conntrack_proto_sctp.c
> > @@ -49,8 +49,8 @@ static const unsigned int
> > sctp_timeouts[SCTP_CONNTRACK_MAX] = {
> >       [SCTP_CONNTRACK_COOKIE_WAIT]            = 3 SECS,
> >       [SCTP_CONNTRACK_COOKIE_ECHOED]          = 3 SECS,
> >       [SCTP_CONNTRACK_ESTABLISHED]            = 210 SECS,
> > -     [SCTP_CONNTRACK_SHUTDOWN_SENT]          = 300 SECS /
> > 1000,
> > -     [SCTP_CONNTRACK_SHUTDOWN_RECD]          = 300 SECS /
> > 1000,
> > +     [SCTP_CONNTRACK_SHUTDOWN_SENT]          = 3 SECS,
> > +     [SCTP_CONNTRACK_SHUTDOWN_RECD]          = 3 SECS,
> >       [SCTP_CONNTRACK_SHUTDOWN_ACK_SENT]      = 3 SECS,
> >       [SCTP_CONNTRACK_HEARTBEAT_SENT]         = 30 SECS,
> >  };
> > @@ -105,7 +105,7 @@ static const u8
> > sctp_conntracks[2][11][SCTP_CONNTRACK_MAX] = {
> >       {
> >  /*   ORIGINAL        */
> >  /*                  sNO, sCL, sCW, sCE, sES, sSS, sSR, sSA, sHS */
> > -/* init         */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sCW},
> > +/* init         */ {sCL, sCL, sCW, sCE, sES, sCL, sCL, sSA, sCW},
> >  /* init_ack     */ {sCL, sCL, sCW, sCE, sES, sSS, sSR, sSA, sCL},
> >  /* abort        */ {sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL, sCL},
> >  /* shutdown     */ {sCL, sCL, sCW, sCE, sSS, sSS, sSR, sSA, sCL},
> > --
> > 2.39.1
>
> FWIW, I like this patch. Should Documentation/networking/nf_conntrack-sysctl.rst be updated to reflect the new timeout values?
Good catch, will post v2 with the 0.3 -> 3 change in nf_conntrack-sysctl.rst.

Thanks for the review.