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

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Message-ID: <CANn89iLVjY+KWs3y=cYW_OpwCLAOt9=x=iTnsPatwzCMYxUpTA@mail.gmail.com>
Date:   Thu, 13 Sep 2018 05:44:20 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     gregkh@...ux-foundation.org
Cc:     mkubecek@...e.cz, maowenan@...wei.com,
        David Woodhouse <dwmw2@...radead.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>,
        Yuchung Cheng <ycheng@...gle.com>, jdw@...zon.de,
        stable@...r.kernel.org, tiwai@...e.de
Subject: Re: [PATCH stable 4.4 0/9] fix SegmentSmack in stable branch (CVE-2018-5390)

On Thu, Sep 13, 2018 at 5:32 AM Greg KH <gregkh@...ux-foundation.org> wrote:
>
> On Thu, Aug 16, 2018 at 05:24:09PM +0200, Greg KH wrote:
> > On Thu, Aug 16, 2018 at 02:33:56PM +0200, Michal Kubecek wrote:
> > > On Thu, Aug 16, 2018 at 08:05:50PM +0800, maowenan wrote:
> > > > On 2018/8/16 19:39, Michal Kubecek wrote:
> > > > >
> > > > > I suspect you may be doing something wrong with your tests. I checked
> > > > > the segmentsmack testcase and the CPU utilization on receiving side
> > > > > (with sending 10 times as many packets as default) went down from ~100%
> > > > > to ~3% even when comparing what is in stable 4.4 now against older 4.4
> > > > > kernel.
> > > >
> > > > There seems no obvious problem when you send packets with default
> > > > parameter in Segmentsmack POC, Which is also very related with your
> > > > server's hardware configuration. Please try with below parameter to
> > > > form OFO packets
> > >
> > > I did and even with these (questionable, see below) changes, I did not
> > > get more than 10% (of one core) by receiving ksoftirqd.
> > >
> > > >       for (i = 0; i < 1024; i++)      // 128->1024
> > > ...
> > > >       usleep(10*1000); // Adjust this and packet count to match the target!, sleep 100ms->10ms
> > >
> > > The comment in the testcase source suggests to do _one_ of these two
> > > changes so that you generate 10 times as many packets as the original
> > > testcase. You did both so that you end up sending 102400 packets per
> > > second. With 55 byte long packets, this kind of attack requires at least
> > > 5.5 MB/s (44 Mb/s) of throughput. This is no longer a "low packet rate
> > > DoS", I'm afraid.
> > >
> > > Anyway, even at this rate, I only get ~10% of one core (Intel E5-2697).
> > >
> > > What I can see, though, is that with current stable 4.4 code, modified
> > > testcase which sends something like
> > >
> > >   2:3, 3:4, ..., 3001:3002, 3003:3004, 3004:3005, ... 6001:6002, ...
> > >
> > > I quickly eat 6 MB of memory for receive queue of one socket while
> > > earlier 4.4 kernels only take 200-300 KB. I didn't test latest 4.4 with
> > > Takashi's follow-up yet but I'm pretty sure it will help while
> > > preserving nice performance when using the original segmentsmack
> > > testcase (with increased packet ratio).
> >
> > Ok, for now I've applied Takashi's fix to the 4.4 stable queue and will
> > push out a new 4.4-rc later tonight.  Can everyone standardize on that
> > and test and let me know if it does, or does not, fix the reported
> > issues?
> >
> > If not, we can go from there and evaluate this much larger patch series.
> > But let's try the simple thing first.
>
> So, is the issue still present on the latest 4.4 release?  Has anyone
> tested it?  If not, I'm more than willing to look at backported patches,
> but I want to ensure that they really are needed here.
>
> thanks,

Honestly, TCP stack without rb-tree for the OOO queue is vulnerable,
even with non malicious sender,
but with big enough TCP receive window and a not favorable network.

So a malicious peer can definitely send packets needed to make TCP
stack behave in O(N), which is pretty bad if N is big...

9f5afeae51526b3ad7b7cb21ee8b145ce6ea7a7a ("tcp: use an RB tree for ooo
receive queue")
was proven to be almost bug free [1], and should be backported if possible.

[1] bug fixed :
76f0dcbb5ae1a7c3dbeec13dd98233b8e6b0b32a tcp: fix a stale ooo_last_skb
after a replace