netdev - RE: [PATCH] net: sctp: Fix negotiation of the number of data streams.

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Message-ID: <a71c0fced85a4f0f98b954b37c3a76ae@AcuMS.aculab.com>
Date:   Tue, 18 Aug 2020 22:10:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Marcelo Ricardo Leitner' <marcelo.leitner@...il.com>
CC:     "'netdev@...r.kernel.org'" <netdev@...r.kernel.org>,
        "'linux-sctp@...r.kernel.org'" <linux-sctp@...r.kernel.org>
Subject: RE: [PATCH] net: sctp: Fix negotiation of the number of data streams.

From: 'Marcelo Ricardo Leitner'
> Sent: 18 August 2020 22:47
> 
> On Tue, Aug 18, 2020 at 02:36:58PM +0000, David Laight wrote:
> > The number of streams offered by the remote system was being ignored.
> > Any data sent on those streams would get discarded by the remote system.
> 
> That's quite brief and not accurate: it was only ignored if 'Xcnt <=
> stream->Xcnt'.

The number of streams (esp out ones) received from the remote
system in an INIT or INIT_ACK was ignored.
So it would always send data chunks using the number of streams
requested by the local user.
I managed to tweak our M3UA config to get invalid stream numbers
sent on both inwards and outwards connections.

I only noticed because of testing a (slightly horrid) workaround
for no longer being able to use kernel_getsockopt() to retrieve
the number of ostreams.
The number of ostreams was about the only thing we didn't trace :-(
At least my code can now obtain the correct value even for buggy
kernels.

> Other than this and the Fixes tag, LGTM. Passes the tests here. I'll
> ack the v2 then.

I wasn't sure whether DM actually wanted a V2 with the fixes
tag fixed.
I can send one tomorrow.

	David

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