netdev - Re: [RFC 0/2] Account for duplicate ACKs with invalid SACK-blocks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 20 Aug 2013 09:36:21 +0200
From:	Christoph Paasch <christoph.paasch@...ouvain.be>
To:	Corey Hickey <bugfood-ml@...ooh.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	Phil Oester <kernel@...uxace.com>,
	Benjamin Hesmans <benjamin.hesmans@...ouvain.be>
Subject: Re: [RFC 0/2] Account for duplicate ACKs with invalid SACK-blocks

On 19/08/13 - 14:22:46, Corey Hickey wrote:
> On 2013-08-19 12:29, Christoph Paasch wrote:
> > There exist sequence-number rewriting middleboxes, who do not modify the 
> > sequence-number in the SACK-blocks.
> > Duplicate acknowledgments with these (invalid) SACK-blocks will not be
> > accounted in sacked_out, and thus no fast-retransmit will trigger.
> > So, the only way to recover from a packet-loss is through an RTO,
> > effectively killing the performance of TCP in this case.
> > 
> > Performance-results can be seen here:
> > http://tools.ietf.org/agenda/87/slides/slides-87-tcpm-11.pdf
> > 
> > Another solution might be to simply disable SACK, as soon as an invalid
> > SACK-block has been received (as suggested by Phil Oester). This however
> > might be too aggressive.
> > 
> > Christoph Paasch (2):
> >   Use acked_out for reno-style ack acounting instead of sacked_out
> >   Account acked_out in sack, if the sack is invalid
> > 
> >  include/linux/tcp.h      |   1 +
> >  include/net/tcp.h        |  17 +++++---
> >  net/ipv4/tcp_input.c     | 103 ++++++++++++++++++++++++++++++++---------------
> >  net/ipv4/tcp_minisocks.c |   1 +
> >  net/ipv4/tcp_output.c    |   6 +--
> >  net/ipv4/tcp_timer.c     |   2 +-
> >  6 files changed, 89 insertions(+), 41 deletions(-)
> 
> I tested this patchset, and, unfortunately, the behavior seems to be the
> same.

Yes, because the problem is still on conntrack's side too.

As soon as conntrack will let pass the invalid SACK-blocks, you will
experience bad performance because every packet-loss can only be recovered
by an RTO.
My patchset tries to fix this last issue.


Cheers,
Christoph

> 
> I'm still planning on working with the Cisco device, when I can get some
> of the network admin's time, but that won't happen immediately.
> 
> Thanks,
> Corey
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html