linux-image-4.15.0-33-generic breaks WiFi

[pureblood]

Since the upgrade from linux-image-4.15.0-32-generic to linux-image-4.15.0-33-generic my Dell XPS 13 L322X laptop is unable to connect to my home WiFi network. It is unable to obtain an IP through DHCP but more in general it seems unable to receive packets. If I set up an IP address manually I still cannot ping my router. There are no noteworthy messages coming through dmesg though. The laptop uses an AR9462 Wireless Network Adapter and not all WiFi networks fail to work (but my home network fails to connect in a reproducible manner). The following step were used to diagnose the problem:

$ uname -a
Linux apol1 4.15.0-33-generic #36-Ubuntu SMP Wed Aug 15 16:00:05 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

$ sudo /etc/init.d/network-manager stop

$ echo -e "network={\n ssid=\"HT_B23514\"\n psk=\"xxxxxxxx\"\n}" > /tmp/wpa_supplicant.conf

$ sudo wpa_supplicant -B -iwlp1s0 -c/tmp/wpa_supplicant.conf -Dwext

$ iwconfig wlp1s0
wlp1s0 IEEE 802.11 ESSID:"HT_B23514"
          Mode:Managed Frequency:2.412 GHz Access Point: 00:16:FB:B2:35:14
          Bit Rate=60 Mb/s Tx-Power=19 dBm
          Retry short limit:7 RTS thr:off Fragment thr:off
          Power Management:off
          Link Quality=70/70 Signal level=-33 dBm
          Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
          Tx excessive retries:1 Invalid misc:48 Missed beacon:0

$ ifconfig wlp1s0
wlp1s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
        inet6 fe80::be85:56ff:fe8f:45f5 prefixlen 64 scopeid 0x20<link>
        ether bc:85:56:8f:45:f5 txqueuelen 1000 (Ethernet)
        RX packets 49 bytes 9692 (9.6 KB)
        RX errors 0 dropped 0 overruns 0 frame 0
        TX packets 68 bytes 15466 (15.4 KB)
        TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

$ sudo dhclient -v wlp1s0
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/wlp1s0/bc:85:56:8f:45:f5
Sending on LPF/wlp1s0/bc:85:56:8f:45:f5
Sending on Socket/fallback
DHCPREQUEST of 10.10.10.2 on wlp1s0 to 255.255.255.255 port 67 (xid=0x247b5867)
DHCPREQUEST of 10.10.10.2 on wlp1s0 to 255.255.255.255 port 67 (xid=0x247b5867)
DHCPDISCOVER on wlp1s0 to 255.255.255.255 port 67 interval 3 (xid=0x16dac52f)
DHCPDISCOVER on wlp1s0 to 255.255.255.255 port 67 interval 4 (xid=0x16dac52f)
DHCPDISCOVER on wlp1s0 to 255.255.255.255 port 67 interval 7 (xid=0x16dac52f)
DHCPDISCOVER on wlp1s0 to 255.255.255.255 port 67 interval 18 (xid=0x16dac52f)
DHCPDISCOVER on wlp1s0 to 255.255.255.255 port 67 interval 20 (xid=0x16dac52f)
DHCPDISCOVER on wlp1s0 to 255.255.255.255 port 67 interval 17 (xid=0x16dac52f)
DHCPDISCOVER on wlp1s0 to 255.255.255.255 port 67 interval 15 (xid=0x16dac52f)
...

The dhclient command never succeeds. If I revert to kernel linux-image-4.15.0-32-generic everything works fine instead:

$ uname -a
Linux apol1 4.15.0-32-generic #35-Ubuntu SMP Fri Aug 10 17:58:07 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

$ sudo /etc/init.d/network-manager stop

$ echo -e "network={\n ssid=\"HT_B23514\"\n psk=\"xxxxxxxx\"\n}" > /tmp/wpa_supplicant.conf

$ sudo wpa_supplicant -B -iwlp1s0 -c/tmp/wpa_supplicant.conf -Dwext

$ iwconfig wlp1s0
wlp1s0 IEEE 802.11 ESSID:"HT_B23514"
          Mode:Managed Frequency:2.412 GHz Access Point: 00:16:FB:B2:35:14
          Bit Rate=144.4 Mb/s Tx-Power=19 dBm
          Retry short limit:7 RTS thr:off Fragment thr:off
          Power Management:off
          Link Quality=70/70 Signal level=-24 dBm
          Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
          Tx excessive retries:1 Invalid misc:12 Missed beacon:0

$ ifconfig wlp1s0
wlp1s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
        inet6 fe80::be85:56ff:fe8f:45f5 prefixlen 64 scopeid 0x20<link>
        ether bc:85:56:8f:45:f5 txqueuelen 1000 (Ethernet)
        RX packets 586 bytes 364645 (364.6 KB)
        RX errors 0 dropped 0 overruns 0 frame 0
        TX packets 684 bytes 191764 (191.7 KB)
        TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

$ sudo dhclient -v wlp1s0
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/wlp1s0/bc:85:56:8f:45:f5
Sending on LPF/wlp1s0/bc:85:56:8f:45:f5
Sending on Socket/fallback
DHCPREQUEST of 10.10.10.2 on wlp1s0 to 255.255.255.255 port 67 (xid=0x518398de)
DHCPACK of 10.10.10.2 from 10.10.10.251
bound to 10.10.10.2 -- renewal in 36342 seconds.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.15.0-33-generic 4.15.0-33.36
ProcVersionSignature: Ubuntu 4.15.0-33.36-generic 4.15.18
Uname: Linux 4.15.0-33-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: genovese 1664 F.... pulseaudio
CurrentDesktop: ubuntu:GNOME
Date: Mon Aug 27 23:35:32 2018
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-12-02 (999 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
MachineType: Dell Inc. Dell System XPS L322X
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-33-generic root=UUID=d3789bb5-1e1a-4f7b-9b85-a43c69bfd1c4 ro quiet splash video.only_lcd=0 vt.handoff=1
RelatedPackageVersions:
 linux-restricted-modules-4.15.0-33-generic N/A
 linux-backports-modules-4.15.0-33-generic N/A
 linux-firmware 1.173.1
SourcePackage: linux
UpgradeStatus: Upgraded to bionic on 2018-04-27 (122 days ago)
dmi.bios.date: 05/15/2013
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A09
dmi.board.name: 0PJHXN
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: 0.1
dmi.modalias: dmi:bvnDellInc.:bvrA09:bd05/15/2013:svnDellInc.:pnDellSystemXPSL322X:pvr:rvnDellInc.:rn0PJHXN:rvrA00:cvnDellInc.:ct8:cvr0.1:
dmi.product.family: ChiefRiver System
dmi.product.name: Dell System XPS L322X
dmi.sys.vendor: Dell Inc.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Would it be possible for you to test the latest upstream stable kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.15 stable kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel-unable-to-test-upstream'.
Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.15.18/

[pureblood (freeseek)]

Okay, I will test this when I get back at home later this evening (EST time). The WiFi at my workplace works fine. Not sure why it selectively fails to work with my home WiFi. If you want to gather any additional info about what differences could be involved please let me know.

[pureblood (freeseek)]

The bug is indeed fixed in the latest v4.15 stable kernel:
$ uname -a
Linux apol1 4.15.18-041518-generic #201804190330 SMP Thu Apr 19 07:34:21 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux