** Description changed: + [Impact] + + Using systemd-resolved to resolve a hostname which has more than 8 CNAME + redirects will fail because of the hard-coded limit. While this case is + somewhat rare, the original reporter demonstrated a real-world scenario + where this happened (although that particular hostname seems to be fixed + now). + + [Test Plan] + + This test plan uses a LXC container to test systemd-resolved on Focal. + If LXD has not been configured on your system, start with: + + $ lxd init --auto + + Then, create a Focal container with: + + $ lxc launch ubuntu-daily:focal focal + + Install dnsmasq-base if needed: + + $ apt install dnsmasq-base + + Stop other DNS servers: + + $ systemctl stop systemd-resolved + $ kill -9 $(pgrep dnsmasq) + + Now, on the host start a new DNS server that listens on lxdbr0, and sets + up an A record, and many CNAME records which ultimately redirect to the + A record: + + $ dnsmasq \ + --cname=test10.lan,test9.lan \ + --cname=test9.lan,test8.lan \ + --cname=test8.lan,test7.lan \ + --cname=test7.lan,test6.lan \ + --cname=test6.lan,test5.lan \ + --cname=test5.lan,test4.lan \ + --cname=test4.lan,test3.lan \ + --cname=test3.lan,test2.lan \ + --cname=test2.lan,test1.lan \ + --cname=test1.lan,test0.lan \ + -k -i lxdbr0 -z -I lo --host-record=test0.lan,$IP + + where $IP is any host on your network. + + Now, obtain a shell in the Focal container: + + $ lxc exec focal bash + + Attempt to resolve test10.lan: + + $ resolvectl query test10.lan + test10.lan: resolve call failed: CNAME loop detected, or CNAME resolving disabled on 'test2.lan' + + On an affected system, the above error will be seen. On a patched + system, the hostname should be resolved. + + [Where problems could occur] + + The patch simply increases the maximum CNAME redirects that are allowed + from 8 to 16, so a reasonable limit is still imposed. If an application + specifically relied on systemd-resolved's limit being at 8, then that + application would potentially see new behavior. + + [Original Description] + On Ubuntu 20.04 (systemd v245.4-4ubuntu3.21), hostname resolution only follows 8 CNAME redirections maximum. So when using a service like Azure Virtual Desktop that has between 9 and 12 redirections, name resolution fails. $ host client.wvd.microsoft.com Host client.wvd.microsoft.com not found: 2(SERVFAIL) $ resolvectl query client.wvd.microsoft.com client.wvd.microsoft.com: resolve call failed: CNAME loop detected, or CNAME resolving disabled on 'waws-prod-zrh-ff7172dd.sip.p.azurewebsites.windows.net' On the other hand it's working fine on Ubuntu 20.04 because CNAME loop limit has been raised from 8 to 16. $ host client.wvd.microsoft.com client.wvd.microsoft.com is an alias for client.privatelink-global.wvd.microsoft.com. client.privatelink-global.wvd.microsoft.com is an alias for client.privatelink.wvd.microsoft.com. client.privatelink.wvd.microsoft.com is an alias for rdweb.wvd.microsoft.com. rdweb.wvd.microsoft.com is an alias for rdweb.privatelink-global.wvd.microsoft.com. rdweb.privatelink-global.wvd.microsoft.com is an alias for rdweb.privatelink.wvd.microsoft.com. rdweb.privatelink.wvd.microsoft.com is an alias for rdweb-prod-geo.trafficmanager.net. rdweb-prod-geo.trafficmanager.net is an alias for mrs-chnor1c101-rdweb-prod.wvd-ase-chnor1c101-prod.p.azurewebsites.net. mrs-chnor1c101-rdweb-prod.wvd-ase-chnor1c101-prod.p.azurewebsites.net is an alias for waws-prod-zrh-63daa049.sip.p.azurewebsites.windows.net. waws-prod-zrh-63daa049.sip.p.azurewebsites.windows.net is an alias for waws-prod-zrh-63daa049.cloudapp.net. waws-prod-zrh-63daa049.cloudapp.net has address 51.107.69.35 - - Here's a quick fix that raises the max CNAME limit from 8 to 16 like it is in Ubuntu 22.04, it fixes the problem for me. + Here's a quick fix that raises the max CNAME limit from 8 to 16 like it + is in Ubuntu 22.04, it fixes the problem for me. Best regards, Vincent. --- systemd-245.4.ORIG/src/resolve/resolved-dns-query.c 2023-06-15 16:58:25.454156663 +0200 +++ systemd-245.4/src/resolve/resolved-dns-query.c 2023-06-01 14:30:09.000000000 +0200 @@ -10,7 +10,7 @@ - #include "resolved-etc-hosts.h" - #include "string-util.h" - + #include "resolved-etc-hosts.h" + #include "string-util.h" + -#define CNAME_MAX 8 +#define CNAME_MAX 16 - #define QUERIES_MAX 2048 - #define AUXILIARY_QUERIES_MAX 64 + #define QUERIES_MAX 2048 + #define AUXILIARY_QUERIES_MAX 64 ProblemType: Bug DistroRelease: Ubuntu 22.04 Package: systemd 249.11-0ubuntu3.9 [modified: usr/lib/sysctl.d/50-default.conf] ProcVersionSignature: Ubuntu 5.19.0-42.43~22.04.1-generic 5.19.17 Uname: Linux 5.19.0-42-generic x86_64 NonfreeKernelModules: nvidia_modeset nvidia ApportVersion: 2.20.11-0ubuntu82.5 Architecture: amd64 CasperMD5CheckResult: unknown CurrentDesktop: ubuntu:GNOME Date: Thu Jun 15 16:53:19 2023 InstallationDate: Installed on 2022-11-22 (205 days ago) InstallationMedia: Error: [Errno 13] Permission denied: '/var/log/installer/media-info' MachineType: Dell Inc. Latitude 5591 ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.19.0-42-generic root=/dev/mapper/AmadeUbuntu22-root ro apparmor=1 security=apparmor audit=1 acpi_rev_override load_nvme=YES nouveau.modeset=0 dis_ucode_ldr quiet splash RebootRequiredPkgs: Error: path contained symlinks. SourcePackage: systemd UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 11/21/2022 dmi.bios.release: 1.25 dmi.bios.vendor: Dell Inc. dmi.bios.version: 1.25.0 dmi.board.name: 0DVVG1 dmi.board.vendor: Dell Inc. dmi.board.version: A00 dmi.chassis.type: 10 dmi.chassis.vendor: Dell Inc. dmi.modalias: dmi:bvnDellInc.:bvr1.25.0:bd11/21/2022:br1.25:svnDellInc.:pnLatitude5591:pvr:rvnDellInc.:rn0DVVG1:rvrA00:cvnDellInc.:ct10:cvr:sku0819: dmi.product.family: Latitude dmi.product.name: Latitude 5591 dmi.product.sku: 0819 dmi.sys.vendor: Dell Inc. modified.conffile..etc.cron.daily.apport: [deleted] mtime.conffile..etc.systemd.journald.conf: 2022-11-22T13:40:37.558934
-- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/2024009 Title: [PATCH] systemd-resolved can't follow more than 8 CNAMEs Status in systemd package in Ubuntu: Fix Released Status in systemd source package in Focal: Triaged Bug description: [Impact] Using systemd-resolved to resolve a hostname which has more than 8 CNAME redirects will fail because of the hard-coded limit. While this case is somewhat rare, the original reporter demonstrated a real-world scenario where this happened (although that particular hostname seems to be fixed now). [Test Plan] This test plan uses a LXC container to test systemd-resolved on Focal. If LXD has not been configured on your system, start with: $ lxd init --auto Then, create a Focal container with: $ lxc launch ubuntu-daily:focal focal Install dnsmasq-base if needed: $ apt install dnsmasq-base Stop other DNS servers: $ systemctl stop systemd-resolved $ kill -9 $(pgrep dnsmasq) Now, on the host start a new DNS server that listens on lxdbr0, and sets up an A record, and many CNAME records which ultimately redirect to the A record: $ dnsmasq \ --cname=test10.lan,test9.lan \ --cname=test9.lan,test8.lan \ --cname=test8.lan,test7.lan \ --cname=test7.lan,test6.lan \ --cname=test6.lan,test5.lan \ --cname=test5.lan,test4.lan \ --cname=test4.lan,test3.lan \ --cname=test3.lan,test2.lan \ --cname=test2.lan,test1.lan \ --cname=test1.lan,test0.lan \ -k -i lxdbr0 -z -I lo --host-record=test0.lan,$IP where $IP is any host on your network. Now, obtain a shell in the Focal container: $ lxc exec focal bash Attempt to resolve test10.lan: $ resolvectl query test10.lan test10.lan: resolve call failed: CNAME loop detected, or CNAME resolving disabled on 'test2.lan' On an affected system, the above error will be seen. On a patched system, the hostname should be resolved. [Where problems could occur] The patch simply increases the maximum CNAME redirects that are allowed from 8 to 16, so a reasonable limit is still imposed. If an application specifically relied on systemd-resolved's limit being at 8, then that application would potentially see new behavior. [Original Description] On Ubuntu 20.04 (systemd v245.4-4ubuntu3.21), hostname resolution only follows 8 CNAME redirections maximum. So when using a service like Azure Virtual Desktop that has between 9 and 12 redirections, name resolution fails. $ host client.wvd.microsoft.com Host client.wvd.microsoft.com not found: 2(SERVFAIL) $ resolvectl query client.wvd.microsoft.com client.wvd.microsoft.com: resolve call failed: CNAME loop detected, or CNAME resolving disabled on 'waws-prod-zrh-ff7172dd.sip.p.azurewebsites.windows.net' On the other hand it's working fine on Ubuntu 20.04 because CNAME loop limit has been raised from 8 to 16. $ host client.wvd.microsoft.com client.wvd.microsoft.com is an alias for client.privatelink-global.wvd.microsoft.com. client.privatelink-global.wvd.microsoft.com is an alias for client.privatelink.wvd.microsoft.com. client.privatelink.wvd.microsoft.com is an alias for rdweb.wvd.microsoft.com. rdweb.wvd.microsoft.com is an alias for rdweb.privatelink-global.wvd.microsoft.com. rdweb.privatelink-global.wvd.microsoft.com is an alias for rdweb.privatelink.wvd.microsoft.com. rdweb.privatelink.wvd.microsoft.com is an alias for rdweb-prod-geo.trafficmanager.net. rdweb-prod-geo.trafficmanager.net is an alias for mrs-chnor1c101-rdweb-prod.wvd-ase-chnor1c101-prod.p.azurewebsites.net. mrs-chnor1c101-rdweb-prod.wvd-ase-chnor1c101-prod.p.azurewebsites.net is an alias for waws-prod-zrh-63daa049.sip.p.azurewebsites.windows.net. waws-prod-zrh-63daa049.sip.p.azurewebsites.windows.net is an alias for waws-prod-zrh-63daa049.cloudapp.net. waws-prod-zrh-63daa049.cloudapp.net has address 51.107.69.35 Here's a quick fix that raises the max CNAME limit from 8 to 16 like it is in Ubuntu 22.04, it fixes the problem for me. Best regards, Vincent. --- systemd-245.4.ORIG/src/resolve/resolved-dns-query.c 2023-06-15 16:58:25.454156663 +0200 +++ systemd-245.4/src/resolve/resolved-dns-query.c 2023-06-01 14:30:09.000000000 +0200 @@ -10,7 +10,7 @@ #include "resolved-etc-hosts.h" #include "string-util.h" -#define CNAME_MAX 8 +#define CNAME_MAX 16 #define QUERIES_MAX 2048 #define AUXILIARY_QUERIES_MAX 64 ProblemType: Bug DistroRelease: Ubuntu 22.04 Package: systemd 249.11-0ubuntu3.9 [modified: usr/lib/sysctl.d/50-default.conf] ProcVersionSignature: Ubuntu 5.19.0-42.43~22.04.1-generic 5.19.17 Uname: Linux 5.19.0-42-generic x86_64 NonfreeKernelModules: nvidia_modeset nvidia ApportVersion: 2.20.11-0ubuntu82.5 Architecture: amd64 CasperMD5CheckResult: unknown CurrentDesktop: ubuntu:GNOME Date: Thu Jun 15 16:53:19 2023 InstallationDate: Installed on 2022-11-22 (205 days ago) InstallationMedia: Error: [Errno 13] Permission denied: '/var/log/installer/media-info' MachineType: Dell Inc. Latitude 5591 ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.19.0-42-generic root=/dev/mapper/AmadeUbuntu22-root ro apparmor=1 security=apparmor audit=1 acpi_rev_override load_nvme=YES nouveau.modeset=0 dis_ucode_ldr quiet splash RebootRequiredPkgs: Error: path contained symlinks. SourcePackage: systemd UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 11/21/2022 dmi.bios.release: 1.25 dmi.bios.vendor: Dell Inc. dmi.bios.version: 1.25.0 dmi.board.name: 0DVVG1 dmi.board.vendor: Dell Inc. dmi.board.version: A00 dmi.chassis.type: 10 dmi.chassis.vendor: Dell Inc. dmi.modalias: dmi:bvnDellInc.:bvr1.25.0:bd11/21/2022:br1.25:svnDellInc.:pnLatitude5591:pvr:rvnDellInc.:rn0DVVG1:rvrA00:cvnDellInc.:ct10:cvr:sku0819: dmi.product.family: Latitude dmi.product.name: Latitude 5591 dmi.product.sku: 0819 dmi.sys.vendor: Dell Inc. modified.conffile..etc.cron.daily.apport: [deleted] mtime.conffile..etc.systemd.journald.conf: 2022-11-22T13:40:37.558934 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/2024009/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
