Public bug reported:
[ Impact ]
* Systemd upstream commit [0] added the new property ID_NET_MANAGED_BY
to allow system admins to explicitly choose what will manage interfaces.
(See bug tracker [1] for details).
* However, in some cases (for example when link state changes), the
ID_NET_MANAGED_BY value is ignored, and systemd-networkd attempts to
reconfigure the interface regardless of the property value.
* This behavior causes conflicts on systems relying on different
network managers alongside systemd-networkd.
* This issue was fixed upstream in [2] and is associated with bug
tracker [3].
[ Test Plan ]
* The original test plan is described in [3] and relies on rebooting VMs.
* To test the change locally without reboots, we can use virtio interfaces on
a VM with the ID_NET_MANAGED_BY property set via udev.
1. Create a custom udev rule to set ID_NET_MANAGED_BY:
$ cat /etc/udev/rules.d/99-debug-unmanaged.rules
SUBSYSTEM=="net", ACTION!="remove", KERNEL=="enp1s0",
ENV{ID_NET_MANAGED_BY}="unmanaged", RUN+="/bin/sh -c 'logger -t debug-udev-test
marked enp1s0 as unmanaged'"
2. Trigger the rule:
$ udevadm trigger --verbose --action=add /sys/class/net/enp1s0
3. Check the state of the interface (Expected: unmanaged):
$ networkctl list
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
2 enp1s0 ether routable unmanaged
4. Change the link state:
$ ip link set enp1s0 down
$ ip link set enp1s0 up
5. Verify state of the interface:
[ FAIL - Current Behavior ]
$ networkctl list
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
2 enp1s0 ether routable configured <-- Incorrectly took control
[ PASS - With Fix Applied ]
$ networkctl list
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
2 enp1s0 ether off unmanaged <-- Correctly ignored
NOTES:
- To set an interface to 'unmanaged', ID_NET_MANAGED_BY can be set to any
string value other than "io.systemd.Network".
[ Where problems could occur ]
* The patch modifies the logic systemd-networkd uses to determine if it
should manage an interface when link is reconfigured. If the logic is
flawed, networkd might incorrectly identify a managed interface as
"unmanaged," leading to a loss of connectivity because networkd will
refuse to configure it.
* Users who have unknowingly set ID_NET_MANAGED_BY (via leftover udev
rules) but were previously relying on the incorrect behavior (where
networkd ignored the flag on link-change and configured the interface
anyway) will have their interfaces unmanaged.
* Patch is already applied to questing and resolute, which reduces
risks of regression.
[ Other Info ]
* Resolute and Questing already include the fix, the change is required in
Noble and Plucky.
* Jammy and older do not implement support for the ID_NET_MANAGED_BY property.
[0] -
https://github.com/systemd/systemd/commit/ba87a61d05d637be9f0b21707f7fe3b0a74c5a05
[1] - https://github.com/systemd/systemd/issues/29768
[2] -
https://github.com/systemd/systemd/commit/78f8d5ed71ecc16ad36d1c215d2d57433d127679
[3] - https://github.com/systemd/systemd/issues/36997
** Affects: systemd (Ubuntu)
Importance: Undecided
Status: Fix Released
** Affects: systemd (Ubuntu Noble)
Importance: Undecided
Status: New
** Affects: systemd (Ubuntu Plucky)
Importance: Undecided
Status: New
** Affects: systemd (Ubuntu Questing)
Importance: Undecided
Status: Fix Released
** Affects: systemd (Ubuntu Resolute)
Importance: Undecided
Status: Fix Released
** Also affects: systemd (Ubuntu Plucky)
Importance: Undecided
Status: New
** Also affects: systemd (Ubuntu Resolute)
Importance: Undecided
Status: New
** Also affects: systemd (Ubuntu Noble)
Importance: Undecided
Status: New
** Also affects: systemd (Ubuntu Questing)
Importance: Undecided
Status: New
** Changed in: systemd (Ubuntu Questing)
Status: New => Fix Released
** Changed in: systemd (Ubuntu Resolute)
Status: New => Fix Released
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https://bugs.launchpad.net/bugs/2133159
Title:
systemd-networkd does not respect ID_NET_MANAGED_BY in all cases
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