netdev - Re: [PATCH stable 4.4 0/9] fix SegmentSmack in stable branch (CVE-2018-5390)

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Date:   Thu, 16 Aug 2018 08:16:21 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Mao Wenan <maowenan@...wei.com>
Cc:     dwmw2@...radead.org, gregkh@...ux-foundation.org,
        netdev@...r.kernel.org, eric.dumazet@...il.com,
        edumazet@...gle.com, davem@...emloft.net, ycheng@...gle.com,
        jdw@...zon.de, stable@...r.kernel.org, Takashi Iwai <tiwai@...e.de>
Subject: Re: [PATCH stable 4.4 0/9] fix SegmentSmack in stable branch
 (CVE-2018-5390)

On Thu, Aug 16, 2018 at 10:50:01AM +0800, Mao Wenan wrote:
> There are five patches to fix CVE-2018-5390 in latest mainline 
> branch, but only two patches exist in stable 4.4 and 3.18: 
> dc6ae4d tcp: detect malicious patterns in tcp_collapse_ofo_queue()
> 5fbec48 tcp: avoid collapses in tcp_prune_queue() if possible
> I have tested with stable 4.4 kernel, and found the cpu usage was very high.
> So I think only two patches can't fix the CVE-2018-5390.
> test results:
> with fix patch：     78.2%   ksoftirqd
> withoutfix patch：   90%     ksoftirqd
> 
> Then I try to imitate 72cd43ba(tcp: free batches of packets in tcp_prune_ofo_queue())
> to drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks with simple queue 
> instead of RB tree. The result is not very well.
>  
> After analysing the codes of stable 4.4, and debuging the 
> system, shows that search of ofo_queue(tcp ofo using a simple queue) cost more cycles.
> 
> So I try to backport "tcp: use an RB tree for ooo receive queue" using RB tree 
> instead of simple queue, then backport Eric Dumazet 5 fixed patches in mainline,
> good news is that ksoftirqd is turn to about 20%, which is the same with mainline now.
> 
> Stable 4.4 have already back port two patches, 
> f4a3313d(tcp: avoid collapses in tcp_prune_queue() if possible)
> 3d4bf93a(tcp: detect malicious patterns in tcp_collapse_ofo_queue())
> If we want to change simple queue to RB tree to finally resolve, we should apply previous 
> patch 9f5afeae(tcp: use an RB tree for ooo receive queue.) firstly, but 9f5afeae have many 
> conflicts with 3d4bf93a and f4a3313d, which are part of patch series from Eric in 
> mainline to fix CVE-2018-5390, so I need revert part of patches in stable 4.4 firstly, 
> then apply 9f5afeae, and reapply five patches from Eric.

There seems to be an obvious mistake in one of the backports. Could you
check the results with Takashi's follow-up fix submitted at

  http://lkml.kernel.org/r/20180815095846.7734-1-tiwai@suse.de

(I would try myself but you don't mention what test you ran.)

Michal Kubecek