Re: [Bug 1889943] Improper TCP/IP packet splitting on e1000e/vmxnet3

[Andrew Melnichenko]

Hi,

Also, as far as I can tell, qemu doesn't support segmentation(if there is no vheader) - performs fragmentation.

And also check https://www.mail-archive.com/qemu-devel@nongnu.org/msg717496.html - there was an issue with IPv6 CSO.

Those patches provide basic IPv6 fragmentation, for now, qemu requires proper work with IPv6 extensions.

On Mon, Aug 3, 2020 at 9:37 AM Yan Vugenfirer <yvugenfi@redhat.com> wrote:

Hello Patrick,

If you are using  QEMU version 4.2, then it is missing recent patches fixing IPv6 and TSO behaviour:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg723411.html
https://www.mail-archive.com/qemu-devel@nongnu.org/msg723412.html

Can you check that the above patches solve your issues?


Best regards,
Yan.

> On 2 Aug 2020, at 6:59 PM, Patrick Magauran <1889943@bugs.launchpad.net> wrote:
>
> Some more clarifications:
> It appears the QEMU does turn on the vnet_hdr flag of the tap interface in most cases, not just host-only networks. My previous assumption was due to the way the libvirt manages it, only setting it if the virtio interface is used.
>
> Still, for software fragmentation implementations, ip fragmentation
> should be a last resort.
>
> I have also confirmed a suspicion that the current implementation of sw
> fragmentation will not work with IPV6. It creates malformed packets as
> ipv6 requires a different setup of headers to fragment. Thanks to the
> many redundancies in the network stack, the packets eventually arrive at
> the host server correctly formed, but we should not rely on this fact.
>
> ** Description changed:
>
> + Update: The sw implementation of fragmentation also creates malformed
> + IPv6 packets when their size is above the MTU. See comment #3
> +
>  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().
> + 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.
>
> --
> You received this bug notification because you are a member of qemu-
> devel-ml, which is subscribed to QEMU.
> https://bugs.launchpad.net/bugs/1889943
>
> Title:
>  Improper TCP/IP packet splitting on e1000e/vmxnet3
>
> Status in QEMU:
>  New
>
> Bug description:
>  Update: The sw implementation of fragmentation also creates malformed
>  IPv6 packets when their size is above the MTU. See comment #3
>
>  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:
> https://bugs.launchpad.net/qemu/+bug/1889943/+subscriptions
>