netdev - Re: [PATCH] sctp: send abort chunk when max

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Date:	Tue, 20 Nov 2012 14:15:14 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH] sctp: send abort chunk when max_retrans exceeded

On Tue, Nov 20, 2012 at 01:44:23PM -0500, Vlad Yasevich wrote:
> On 11/20/2012 12:59 PM, Neil Horman wrote:
> >In the event that an association exceeds its max_retrans attempts, we should
> >send an ABORT chunk indicating that we are closing the assocation as a result.
> >Because of the nature of the error, its unlikely to be received, but its a nice
> >clean way to close the association if it does make it through, and it will give
> >anyone watching via tcpdump a clue as to what happened.
> >
> >Signed-off-by: Neil Horman <nhorman@...driver.com>
> >CC: Vlad Yasevich <vyasevich@...il.com>
> >CC: "David S. Miller" <davem@...emloft.net>
> >CC: linux-sctp@...r.kernel.org
> >---
> >  include/net/sctp/sm.h    |  2 ++
> >  net/sctp/sm_make_chunk.c | 26 +++++++++++++++++++++-----
> >  net/sctp/sm_sideeffect.c |  9 ++++++++-
> >  3 files changed, 31 insertions(+), 6 deletions(-)
> >
> >diff --git a/include/net/sctp/sm.h b/include/net/sctp/sm.h
> >index b5887e1..2a82d13 100644
> >--- a/include/net/sctp/sm.h
> >+++ b/include/net/sctp/sm.h
> >@@ -234,6 +234,8 @@ struct sctp_chunk *sctp_make_abort_violation(const struct sctp_association *,
> >  struct sctp_chunk *sctp_make_violation_paramlen(const struct sctp_association *,
> >  				   const struct sctp_chunk *,
> >  				   struct sctp_paramhdr *);
> >+struct sctp_chunk *sctp_make_violation_max_retrans(const struct sctp_association *,
> >+						   const struct sctp_chunk *);
> >  struct sctp_chunk *sctp_make_heartbeat(const struct sctp_association *,
> >  				  const struct sctp_transport *);
> >  struct sctp_chunk *sctp_make_heartbeat_ack(const struct sctp_association *,
> >diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> >index fbe1636..d6a8c80 100644
> >--- a/net/sctp/sm_make_chunk.c
> >+++ b/net/sctp/sm_make_chunk.c
> >@@ -1074,17 +1074,33 @@ struct sctp_chunk *sctp_make_violation_paramlen(
> >  {
> >  	struct sctp_chunk *retval;
> >  	static const char error[] = "The following parameter had invalid length:";
> >-	size_t payload_len = sizeof(error) + sizeof(sctp_errhdr_t) +
> >-				sizeof(sctp_paramhdr_t);
> >+	size_t payload_len = sizeof(error) + sizeof(sctp_errhdr_t);
> >
> >  	retval = sctp_make_abort(asoc, chunk, payload_len);
> >  	if (!retval)
> >  		goto nodata;
> >
> >-	sctp_init_cause(retval, SCTP_ERROR_PROTO_VIOLATION,
> >-			sizeof(error) + sizeof(sctp_paramhdr_t));
> >+	sctp_init_cause(retval, SCTP_ERROR_PROTO_VIOLATION, sizeof(error));
> >+	sctp_addto_chunk(retval, sizeof(error), error);
> >+
> >+nodata:
> >+	return retval;
> >+}
> 
> Neil
> 
> You ended dropping the parameter information of the parameter that
> caused the violation.  Was that intentional?
> 
Yes, it was, because theres not really IMO a specific parameter that causes this
abort condition.  If a chunk needs to be resent more than max_retrans times, we
abort the connection, theres no specific parameter that we can point to that
says "this caused the problem", we're just aborting because we can't get a SACK 
from the peer.  Likewise, I can't think of any information that we can include
that would give the peer, or the anyone tcpdumping the connection an improved
view as to why the abort happened, beyond the string this patch currently
includes.

I know I had privately sent you an early version of the patch as a rough draft
which did include space for a param header, but that patch never filled that
space out, since we don't have any valid information to fill it out with.

Thanks & Regards
Neil
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