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Message-ID: <b11d08ee-d298-d11a-5caf-4a3c8860ddb4@leemhuis.info>
Date: Fri, 30 Sep 2022 09:36:28 +0200
From: Thorsten Leemhuis <regressions@...mhuis.info>
To: Mike Manning <mvrmanning@...il.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Maximilien Cuony <maximilien.cuony@...anite.ch>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
"regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Subject: Re: [REGRESSION] Unable to NAT own TCP packets from another VRF with
tcp_l3mdev_accept = 1
Hi, this is your Linux kernel regression tracker.
CCing the regression mailing list, as it should be in the loop for all
regressions, as explained here:
https://www.kernel.org/doc/html/latest/admin-guide/reporting-issues.html
Also adding the author of the bisected commit, Mike Manning to the list
of recipients.
For the rest of this mail:
[TLDR: I'm adding this regression report to the list of tracked
regressions; all text from me you find below is based on a few templates
paragraphs you might have encountered already already in similar form.]
On 28.09.22 16:02, Maximilien Cuony wrote:
>
> We're using VRF with a machine used as a router and have a specific
> issue where the router doesn't handle his own packets correctly during
> NATing if the packet is coming from a different VRF.
>
> We had the issue with debian buster (4.19), but the issue solved itself
> when we updated to debian bullseye (5.10.92).
>
> However, during an upgrade of debian bullseye to the latest kernel, the
> issue appeared again (5.10.140).
>
> We did a bisection and this leaded us to
> "b0d67ef5b43aedbb558b9def2da5b4fffeb19966 net: allow unbound socket for
> packets in VRF when tcp_l3mdev_accept set [ Upstream commit
> 944fd1aeacb627fa617f85f8e5a34f7ae8ea4d8e ]".
>
> Simplified case setup:
>
> There is two machines in the setup. They both forward packets
> (net.ipv4.ip_forward = 1) and there is two interface between them.
>
> The main machine has two VRF. The default VRF is using the second
> machine as the default route, on a specific interface.
> The second machine has as default route to main machine, on the other
> VRF using the second pair of interfaces.
>
> On the main machine, the second interface is in a specific VRF. In that
> VRF, packets are NATed to the internet on a third interface.
>
> A visual schema with the normal flow is available there:
> https://etinacra.ch/kernel.png
>
> Configuration command:
>
> Main machine:
> sysctl -w net.ipv4.tcp_l3mdev_accept = 1
> sysctl -w systnet.ipv4.ip_forward = 1
> iptables -t raw -A PREROUTING -i eth0 -j CT --zone 5
> iptables -t raw -A OUTPUT -o eth0 -j CT --zone 5
> iptables -t nat -A POSTROUTING -o eth2 -j SNAT --to 192.168.1.1
> cat /etc/network/interfaces
>
> auto firewall
> iface firewall
> vrf-table 1200
>
> auto eth0
> iface eth0
> address 192.168.5.1/24
> gateway 192.168.5.2
>
> auto eth1
> iface eth1
> address 192.168.10.1/24
> vrf firewall
> up ip route add 192.168.5.0/24 via 192.168.10.2 vrf firewall
>
> auto eth2
> iface eth2
> address 192.168.1.1/24
> gateway 192.168.1.250
> vrf firewall
>
> ==
>
> Second machine:
>
> sysctl -w net.ipv4.ip_forward = 1
>
> cat /etc/network/interfaces
>
> auto eth0
> iface eth0
> address 192.168.5.2/24
>
> auto eth1
> iface eth1
> address 192.168.10.2/24
> gateway 192.168.10.1
>
> ==
>
> Without issue, if we look at a tcpdump on all interface on the main
> machine, everything is fine (output truncated):
>
> 10:28:32.811283 eth0 Out IP 192.168.5.1.55750 > 99.99.99.99.80: Flags
> [S], seq 2216112145
> 10:28:32.811666 eth1 In IP 192.168.5.1.55750 > 99.99.99.99.80: Flags
> [S], seq 2216112145
> 10:28:32.811679 eth2 Out IP 192.168.1.1.55750 > 99.99.99.99.80: Flags
> [S], seq 2216112145
> 10:28:32.835138 eth2 In IP 99.99.99.99.80 > 192.168.1.1.55750: Flags
> [S.], seq 383992840, ack 2216112146
> 10:28:32.835152 eth1 Out IP 99.99.99.99.80 > 192.168.5.1.55750: Flags
> [S.], seq 383992840, ack 2216112146
> 10:28:32.835457 eth0 In IP 99.99.99.99.80 > 192.168.5.1.55750: Flags
> [S.], seq 383992840, ack 2216112146
> 10:28:32.835511 eth0 Out IP 192.168.5.1.55750 > 99.99.99.99.80: Flags
> [.], ack 1, win 502
>
> However when the issue is present, the SYNACK does arrives on eth2, but
> is never "unNATed" back to eth1:
>
> 10:25:07.644433 eth0 Out IP 192.168.5.1.48684 > 99.99.99.99.80: Flags
> [S], seq 3207393154
> 10:25:07.644782 eth1 In IP 192.168.5.1.48684 > 99.99.99.99.80: Flags
> [S], seq 3207393154
> 10:25:07.644793 eth2 Out IP 192.168.1.1.48684 > 99.99.99.99.80: Flags
> [S], seq 3207393154
> 10:25:07.668551 eth2 In IP 54.36.61.42.80 > 192.168.1.1.48684: Flags
> [S.], seq 823335485, ack 3207393155
>
> The issue is only with TCP connections. UDP or ICMP works fine.
>
> Turing off net.ipv4.tcp_l3mdev_accept back to 0 also fix the issue, but
> we need this flag since we use some sockets that does not understand VRFs.
>
> We did have a look at the diff and the code of inet_bound_dev_eq, but we
> didn't understand much the real problem - but it does seem now that
> bound_dev_if if now checked not to be False before the bound_dev_if ==
> dif || bound_dev_if == sdif comparison, something that was not the case
> before (especially since it's dependent on l3mdev_accept).
>
> Maybe our setup is wrong and we should not be able to route packets like
> that?
>
> Thanks a lot and have a nice day!
>
> Maximilien Cuony
Thanks for the report. To be sure below issue doesn't fall through the
cracks unnoticed, I'm adding it to regzbot, my Linux kernel regression
tracking bot:
#regzbot ^introduced b0d67ef5b43aedbb558b9d
#regzbot ignore-activity
This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply -- ideally with also
telling regzbot about it, as explained here:
https://linux-regtracking.leemhuis.info/tracked-regression/
Reminder for developers: When fixing the issue, add 'Link:' tags
pointing to the report (the mail this one replies to), as explained for
in the Linux kernel's documentation; above webpage explains why this is
important for tracked regressions.
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