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 07:59:21 +0000
From: Sriram Yagnaraman <sriram.yagnaraman@....tech>
To: Xin Long <lucien.xin@...il.com>, 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>
CC: "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



> -----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?