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

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Message-ID: <20180816065210.iq7jyscajjoiw7k4@unicorn.suse.cz>
Date:   Thu, 16 Aug 2018 08:52:10 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     maowenan <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 02:42:32PM +0800, maowenan wrote:
> On 2018/8/16 14:16, Michal Kubecek wrote:
> > 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.)
> 
> I have backport RB tree in stable 4.4, function
> tcp_collapse_ofo_queue() has been refined, which keep the same with
> mainline, so it seems no problem when apply Eric's patch 3d4bf93a(tcp:
> detect malicious patterns in tcp_collapse_ofo_queue()).
> 
> I also noticed that range_truesize != head->truesize will be always
> false which mentioned in your URL, but this only based on stable 4.4's
> codes, If I applied RB tree's patch 9f5afeae(tcp: use an RB tree for
> ooo receive queue), and after apply 3d4bf93a,the codes should be
> range_truesize += skb->truesize, and range_truesize != head->truesize
> can be true.

My point is that backporting all this into stable 4.4 is quite intrusive
so that if we can achieve similar results with a simple fix of an
obvious omission, it would be preferrable.

Michal Kubecek