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From: Patrick Magauran <1889943@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1889943] Re: Improper TCP/IP packet splitting on e1000e/vmxnet3
Date: Sun, 02 Aug 2020 04:29:37 -0000
Message-ID: <159634257744.3361.8442021489420408279.malone@gac.canonical.com> (raw)
In-Reply-To: <159622949743.5060.8912306868276612545.malonedeb@soybean.canonical.com>

After stepping through the code, it has become clear that the
e1000e/vmxnet3 emulated models do not implement TCP segmentation,
however they still "advertise" it as a feature to the guest OS.

Regarding my prior interpretation, the implementation is written to
forward the entire packet to the host OS if the has_vnet_hdr variable is
set, which is passed all the way up from the IFF_VNET_HDR on the tap/tun
interface. I am not sure what the kernel considers when setting that
flag, but it appears that it is true when in a host-only configuration,
and false otherwise. I may look into the virtio implementation to see
how it affects that because they are linked.

In order to fix this, it would likely be possible to modify the
net_tx_pkt_do_sw_fragmentation function in net_tx_pkt.c to incorporate
the full set of offloads, not just ipv4.

Because both the e1000e and the vmxnet3 implmentations share net_tx_pkt
functions, this could fix both.

You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

  Improper TCP/IP packet splitting on e1000e/vmxnet3

Status in QEMU:

Bug description:
  Problem Description:
  When using a tap interface and the guest sends a TCP packet that would need to be segmented, it is fragmented using IP fragmentation. The host does not reassemble the IP fragments and forwards them to the next hop. This causes issues on certain ISPs, which seemingly reject IP fragments(Verizon Fios). 
  This issue occurs on the e1000e and vmxnet3 NIC models, and possibly others. It does not occur on the virtio(which passes the entire packet through to the host w/o fragmentation or segmentation) or the e1000 model(). 

  Test scenario:
  Setup a tap and network bridge using the directions here: https://gist.github.com/extremecoders-re/e8fd8a67a515fee0c873dcafc81d811c
  Boot the machine into any modern guest(a Fedora 31 live iso was used for testing)
  Begin a wireshark capture on the host machine
  On the host(or another machine on the network) run: npx http-echo-server(See https://github.com/watson/http-echo-server)
  On the guest run
  Curl -d “Lorem ipsum dolor sit amet, consectetur adipiscing elit. Maecenas venenatis viverra ipsum, ac tincidunt est rhoncus eu. Suspendisse vehicula congue ante, non rhoncus elit tempus vitae. Duis ac leo massa. Donec rutrum condimentum turpis nec ultricies. Duis laoreet elit eu arcu pulvinar, vitae congue neque mattis. Mauris sed ante nunc. Vestibulum vitae urna a tellus maximus sagittis. Vivamus luctus pellentesque neque, vel tempor purus porta ut. Phasellus at quam bibendum, fermentum libero sit amet, ullamcorper mauris. In rutrum sit amet dui id maximus. Ut lectus ligula, hendrerit nec aliquam non, finibus a turpis. Proin scelerisque convallis ante, et pharetra elit. Donec nunc nisl, viverra vitae dui at, posuere rhoncus nibh. Mauris in massa quis neque posuere placerat quis quis massa. Donec quis lacus ligula. Donec mollis vel nisi eget elementum. Nam id magna porta nunc consectetur efficitur ac quis lorem. Cras faucibus vel ex porttitor mattis. Praesent in mattis tortor. In venenatis convallis quam, in posuere nibh. Proin non dignissim massa. Cras at mi ut lorem tristique fringilla. Nulla ac quam condimentum metus tincidunt vulputate ut at leo. Nunc pellentesque, nunc vel rhoncus condimentum, arcu sem molestie augue, in suscipit mauris odio mollis odio. Integer hendrerit lectus a leo facilisis, in accumsan urna maximus. Nam nec odio volutpat, varius est id, tempus libero. Vestibulum lobortis tortor quam, ac scelerisque urna rhoncus in. Etiam tempor, est sit amet vulputate molestie, urna neque sodales leo, sit amet blandit risus felis sed est. Nulla eu eros nec tortor dapibus maximus faucibus ut erat. Ut pharetra tempor massa in bibendum. Interdum et malesuada fames ac ante ipsum primis in faucibus. Etiam mattis molestie felis eu efficitur. Morbi tincidunt consectetur diam tincidunt feugiat. Morbi euismod ut lorem finibus pellentesque. Aliquam eu porta ex. Aliquam cursus, orci sit amet volutpat egestas, est est pulvinar erat, sed luctus nisl ligula eget justo vestibulum.” <ECHOSERVERIP:PORT>

  2000 bytes of Lorem Ipsum taken from https://www.lipsum.com/

  Compare results from an e1000, a virtio, and a e1000e card:
  | Model  | Fragment  | Segment | Wire Size  |
  | e1000e | Yes       | NO      | 1484 + 621 |
  | e1000  | No        | Yes     | 1516 + 620 |
  | Virtio | NO        | NO      | 2068       |

  Expected Results:
  TCP Segment to proper size OR pass full size to host and let the host split if necessary.

  Configuration changes that did not work:
  Disable host, guest, router firewalls
  Different Hosts
  Different Physical NICs
  Libvirt based NAT/Routed modes
  Fedora 32 vs 31
  Qemu 4.2.0 vs github commit d74824cf7c8b352f9045e949dc636c7207a41eee

  System Information:
  lsb_release -rd
  Description:	Fedora release 32 (Thirty Two)
  Release:	32

  uname -a
  Linux pats-laptop-linux 5.7.10-201.fc32.x86_64 #1 SMP Thu Jul 23 00:58:39 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

  I can provide additional logs, debug info, etc. if needed.

To manage notifications about this bug go to:

  parent reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-31 21:04 [Bug 1889943] [NEW] " Patrick Magauran
2020-08-01  1:23 ` [Bug 1889943] " Patrick Magauran
2020-08-02  4:29 ` Patrick Magauran [this message]
2020-08-02 15:59 ` Patrick Magauran
2020-08-03  6:37   ` [Bug 1889943] " Yan Vugenfirer
2020-08-03  8:53     ` Andrew Melnichenko
2020-08-03 19:28     ` Patrick J. Magauran
2020-08-03 19:28       ` Patrick Magauran

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