Bug#1056350: systemd: network int is stuck in "configuring" state if IPv6 RA msg deprecates a short-lived prefix

[Martin Tonusoo]

Package: systemd
Version: 252.17-1~deb12u1
Severity: normal
X-Debbugs-Cc: martin at tonusoo.ee

A network interface is stuck in "configuring" state in the output of
"networkctl" if a prefix advertised by IPv6 router advertisement
message is shortly(~1 second) deprecated by another IPv6 RA message.
Interface will stay in "configuring" state as long as the
systemd-networkd is restarted.

One can replicate this issue by executing the script below in IPv6
router:

---
#!/usr/bin/env bash

cat <<-EOF > /etc/radvd.conf
interface br0
{
    AdvSendAdvert on;
    MinRtrAdvInterval 60;
    MaxRtrAdvInterval 180;
    prefix 2001:db8:1234:1234::/64 { DecrementLifetimes on; AdvValidLifetime 60; AdvPreferredLifetime 60; };
};
EOF

systemctl reload radvd.service

sleep 1

cat <<-EOF > /etc/radvd.conf
interface br0
{
    AdvSendAdvert on;
    MinRtrAdvInterval 60;
    MaxRtrAdvInterval 180;
    prefix 2001:db8:1234:1234::/64 { DecrementLifetimes off; AdvValidLifetime 0; AdvPreferredLifetime 0; };
};
EOF

systemctl reload radvd.service
---

It often takes multiple tries to evoke the described behavior. The host network interface configuration is following:
---
[Match]
Name=ens7

[Network]
DHCP=yes
---

"IPv6AcceptRA=" is "enabled". The network interface stuck in "configuring"
state logs(systemd-networkd has debug logging enabled) following when
receiving the RA messages from the router:

Nov 21 14:27:39 hr-d1 systemd-networkd[272]: ens7: NDISC: Received Router Advertisement: flags none preference medium lifetime 540 sec
Nov 21 14:27:39 hr-d1 systemd-networkd[272]: ens7: NDISC: Invoking callback for 'router' event.
Nov 21 14:27:39 hr-d1 systemd-networkd[272]: ens7: Requesting NDisc route (configuring,configured): dst: n/a, src: n/a, gw: fe80::a7:29ff:fea6:ec61, prefsrc: n/a, scope: global, table: main(254), proto: ra, type: unicast, nexthop: 0, priority: 1024, flags: n/a
Nov 21 14:27:39 hr-d1 systemd-networkd[272]: ens7: link_check_ready(): address 2001:db8:1234:1234:5054:ff:fe34:429d/64 is not ready.
Nov 21 14:27:39 hr-d1 systemd-networkd[272]: ens7: Setting SLAAC addresses and router.
Nov 21 14:27:39 hr-d1 systemd-networkd[272]: ens7: link_check_ready(): address 2001:db8:1234:1234:5054:ff:fe34:429d/64 is not ready.
Nov 21 14:27:39 hr-d1 systemd-networkd[272]: ens7: Configuring NDisc route (requesting,configuring,configured): dst: n/a, src: n/a, gw: fe80::a7:29ff:fea6:ec61, prefsrc: n/a, scope: global, table: main(254), proto: ra, type: unicast, nexthop: 0, priority: 1024, flags: n/a
Nov 21 14:27:39 hr-d1 systemd-networkd[272]: ens7: ndisc_check_ready(): no SLAAC address is ready.


2001:db8:1234:1234:5054:ff:fe34:429d/64 is the address which was
configured on ens7 for a second. fe80::a7:29ff:fea6:ec61
is the link-local address of the router sending the RA message.

The issue seems to be fixed in version 254.5-1~bpo12+2 from
bookworm-backports.


-- Package-specific info:

-- System Information:
Debian Release: 12.2
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.1.0-13-amd64 (SMP w/2 CPU threads; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages systemd depends on:
ii  libacl1            2.3.1-3
ii  libaudit1          1:3.0.9-1
ii  libblkid1          2.38.1-5+b1
ii  libc6              2.36-9+deb12u3
ii  libcap2            1:2.66-4
ii  libcryptsetup12    2:2.6.1-4~deb12u1
ii  libfdisk1          2.38.1-5+b1
ii  libgcrypt20        1.10.1-3
ii  libkmod2           30+20221128-1
ii  liblz4-1           1.9.4-1
ii  liblzma5           5.4.1-0.2
ii  libmount1          2.38.1-5+b1
ii  libp11-kit0        0.24.1-2
ii  libseccomp2        2.5.4-1+b3
ii  libselinux1        3.4-1+b6
ii  libssl3            3.0.11-1~deb12u2
ii  libsystemd-shared  252.17-1~deb12u1
ii  libsystemd0        252.17-1~deb12u1
ii  libzstd1           1.5.4+dfsg2-5
ii  mount              2.38.1-5+b1

Versions of packages systemd recommends:
ii  dbus [default-dbus-system-bus]   1.14.10-1~deb12u1
ii  systemd-timesyncd [time-daemon]  252.17-1~deb12u1

Versions of packages systemd suggests:
ii  libfido2-1             1.12.0-2+b1
pn  libqrencode4           <none>
pn  libtss2-esys-3.0.2-0   <none>
pn  libtss2-mu0            <none>
pn  libtss2-rc0            <none>
pn  polkitd | policykit-1  <none>
pn  systemd-boot           <none>
pn  systemd-container      <none>
pn  systemd-homed          <none>
pn  systemd-resolved       <none>
pn  systemd-userdbd        <none>

Versions of packages systemd is related to:
ii  dbus-user-session  1.14.10-1~deb12u1
pn  dracut             <none>
ii  initramfs-tools    0.142
ii  libnss-systemd     252.17-1~deb12u1
ii  libpam-systemd     252.17-1~deb12u1
ii  udev               252.17-1~deb12u1

-- no debconf information