This bug was fixed in the package isc-dhcp - 4.4.1-2.1ubuntu5.20.04.5
---
isc-dhcp (4.4.1-2.1ubuntu5.20.04.5) focal; urgency=medium
[ Mauricio Faria de Oliveira ]
* Prevent race condition that might ignore DHCP OFFERs/ACKs
when dhclient receives DHCP traffic noise. (LP:
This bug was fixed in the package isc-dhcp - 4.4.1-2.3ubuntu2.4
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isc-dhcp (4.4.1-2.3ubuntu2.4) jammy; urgency=medium
[ Mauricio Faria de Oliveira ]
* Prevent race condition that might ignore DHCP OFFERs/ACKs
when dhclient receives DHCP traffic noise. (LP: #1926139)
The
The -proposed packages have also been verified by the Microsoft Azure team.
14k+ VM deployments with the fix didn't observe the issue over the weekend.
Marking jammy/focal as verified based on that plus 2 synthetic tests
above.
** Tags removed: verification-needed verification-needed-focal
verification done on focal
(full steps in comment #9)
The issue is not reproducible with the package in -proposed,
and is reproducible with the 2 switches for the old behavior
(DHCP_FD_FLAGS_POKE=0 or dhcp.fd_flags_poke=0), as expected.
...
# add-apt-repository -y 'deb
verification done on jammy
(full steps in comment #9)
The issue is not reproducible with the package in -proposed,
and is reproducible with the 2 switches for the old behavior
(DHCP_FD_FLAGS_POKE=0 or dhcp.fd_flags_poke=0), as expected.
...
# add-apt-repository -yp proposed
# apt policy
Hello Martijn, or anyone else affected,
Accepted isc-dhcp into focal-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/isc-
dhcp/4.4.1-2.1ubuntu5.20.04.5 in a few hours, and then in the -proposed
repository.
Please help us by testing this new package.
Hello Martijn, or anyone else affected,
Accepted isc-dhcp into jammy-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/isc-
dhcp/4.4.1-2.3ubuntu2.4 in a few hours, and then in the -proposed
repository.
Please help us by testing this new package. See
** Tags added: se-sru-sponsor-mfo
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https://bugs.launchpad.net/bugs/1926139
Title:
dhclient: thread concurrency race leads to DHCPOFFER packets not being
>From the 'Where problems could occur' section.
Considerations on regressions and approaches.
[Where problems could occur]
isc-dhcp is a core package, and any change comes with the risk that
users would not be able to receive dhcp leases with dhclient, leaving
their systems with no IP address
From the 'Other Info' section.
Detailed analysis of the issue and more.
[Other Info]
Full log: https://paste.ubuntu.com/p/8yBfw2KR5h/
Log of a working run: https://paste.ubuntu.com/p/N3ZgqrxyQD/
When you tcpdump dhclient, we see all DHCPDISCOVER packets being replied
to with DHCPOFFER packets,
Pressing Page Down 17 times to go over the bug description sounds like a
new record! ;-)
Just in case future reviewers don't find that as exciting while going
through reviews, I'll move some text into comments and reference them
from the description.
** Bug watch added:
Jammy/22.04:
- test packages in ppa:mfo/lp1926139
- reproduction steps delta (based on comment #9)
...
Reproducer based on GDB and DHCP noise injection.
It uses 3 veth pairs (DHCP server/client/injector,
the latter two under namespaces) on a linux bridge.
...
LXD VM:
lxc launch ubuntu:jammy
** Patch added: "lp1926139_focal_isc-dhcp_v2.debdiff"
https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1926139/+attachment/5643626/+files/lp1926139_focal_isc-dhcp_v2.debdiff
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Test packages:
https://launchpad.net/~mfo/+archive/ubuntu/lp1926139
isc-dhcp 4.4.1-2.1ubuntu5.20.04.4+lp1926139.2
Default behavior: issue fixed.
---
(gdb) break omapip/dispatch.c:333
(gdb) commands
shell sleep 0.2
continue
end
(gdb) run -d -v
Hey Matthew, Chris,
Apparently there's a simpler, less intrusive, and more specific way to
do this.
Apologies that I missed this earlier, but I found more about the
possibilities in bind9-libs functions while checking the previous fix
approach for regressions.
Could you please provide your
** Description changed:
[Impact]
Occasionally, during instance boot or machine start-up, dhclient will
attempt to acquire a dhcp lease and fail, leaving the instance with no
IP address and making it unreachable.
This happens about once every 100 reboots on bare metal, or Chris
Great work Maurico, I think you make several excellent points and I
appreciate your efforts on a better reproducer and alternative patch.
FWIW I began testing the Matthew's initial build (which disabled
threads) against a large number of VMs and that appeared to address the
issues we're seeing.
** Patch added: "lp1926139_focal_isc-dhcp.debdiff"
https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1926139/+attachment/5642442/+files/lp1926139_focal_isc-dhcp.debdiff
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Hi Matthew,
Thanks for the excellent analysis and considerate fix proposal, as
always!
I looked at this for the last couple of days, for potential sponsorship.
I have attentively gone through the SRU template and Other Info section,
and considered the proposal to switch bind9-libs into
Reproducer based on GDB and DHCP noise injection.
It uses 3 veth pairs (DHCP server/client/injector,
the latter two under namespaces) on a linux bridge.
LXD VM:
$ lxc launch ubuntu:focal lp1926139-focal --vm
$ lxc shell lp1926139-focal
Network Setup:
# ip link add br0
** Tags removed: sts-sponsor
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https://bugs.launchpad.net/bugs/1926139
Title:
dhclient: thread concurrency race leads to DHCPOFFER packets not being
** Tags added: sts-sponsor
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https://bugs.launchpad.net/bugs/1926139
Title:
dhclient: thread concurrency race leads to DHCPOFFER packets not being
Screenshot of wireshark.
** Attachment added: "Screenshot of wireshark"
https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1926139/+attachment/5641811/+files/Screenshot_2023-01-17-16-14-21_1920x1200%250A1920x1080%250A1920x1080.png
** Description changed:
[Impact]
Occasionally,
packet capture from a reproduction run
** Description changed:
- Platform: Qemu/libvirt on AMD64
- Ubuntu version: 20.04
- isc-dhcp-client version: 4.4.1-2.1ubuntu5
- Problem: When dhclient is used during boot every few reboots the DHCP OFFER
packets aren't pushed from the kernel to dhclient.
** Summary changed:
- dhclient doesn't receive dhcp offer from kernel
+ dhclient: thread concurrency race leads to DHCPOFFER packets not being
received
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