Hey Dan! I see some autopkgtests failing for this upload for artful, I re-ran them to see how frequently those are reproducible. The systemd one is flaky, but I would like someone to take a look at the network- manager ones.
-- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to isc-dhcp in Ubuntu. https://bugs.launchpad.net/bugs/1718568 Title: dhclient-script fails to wait for link-local address Status in isc-dhcp package in Ubuntu: Fix Released Status in isc-dhcp source package in Trusty: Fix Committed Status in isc-dhcp source package in Xenial: Fix Committed Status in isc-dhcp source package in Zesty: Won't Fix Status in isc-dhcp source package in Artful: Fix Committed Status in isc-dhcp source package in Bionic: Fix Released Status in isc-dhcp package in Debian: New Bug description: [impact] bug 1633479 made a change to isc-dhcp to wait for an interface's link-local ipv6 address to switch from 'tentative' to normal, because all link-local addresses briefly go through a 'tentative' state while the kernel is performing ipv6 link-local 'duplicate address detection' (DAD). While in the 'tentative' state, dhclient can't take over the interface and send out dhcpv6 requests; it must wait until DAD completes. However, the change made in that bug does not account for the case where the 'tentative' check is done before the interface has even set up a link-local address; its case statement assumes if there is no 'tentative' or 'dadfailed' string in the output, the link-local address is ready to use. When the address check finds no address at all, this will return as successful, even though it shouldn't, and dhclient will fail to get the dhcpv6 address. [test case] on a system that is configured for dhcpv6 on one or more of its interfaces, repeatedly try to get the dhcpv6 address. For interfaces that are slower to actually set up their initial tentative link-local address, they will occasionally fail, since the current code is a race between the kernel adding the tentative link-local address, and the dhclient-script.linux code checking the interface for a tentative address. with the patch to correct this, even interfaces slow to add their tentative link-local address should correctly wait for the address to get added, and then transition from tentative to normal, and then begin the dhcpv6 process. [regression potential] errors in this function can cause dhclient to fail to get a ipv6 address for an interface; regression would happen if this patch makes it fail more than it already is failing, but would not cause other failures or problems after getting an ipv6 address; this patch will affect only startup-time. additionally, the current behavior of dhclient when using an interface that has no link-local address after being brought up is to exit immediately; while after this patch dhclient will wait ~6 seconds before exiting (while waiting for the interface to get a non-tentative link-local addr). This is the point of this bug, that some NIC hw doesn't show a tentative link-local addr immediately after coming up. However, if dhclient -6 is configured to run on an interface without any link state at all (e.g. its physical cable is unplugged), then while before dhclient would exit immediately with error, it now waits 6 seconds. If the system is misconfigured like that, or if someone pulls a cable and reboots, then system boot will be delayed an extra 6 seconds. However, that short delay for misconfigured/broken systems seems acceptable to me, in exchange for allowing dhclient to work with slightly slow NIC hw. Additionally, consider that if the problem is instead no dhcpv6 server, dhclient -6 will wait a much, much longer amount of time for a dhcpv6 response before giving up. [other info] related bug 1633479 [original description] Summary: ======== If a interface does not yet have a link-local address (as it may have just been brought up), dhclient -6 <ifname> will fail. The built-in "wait for link-local address" loop does not function properly, causing DHCP failure. Discussion: =========== In trying to configure isc-dhcp-client 4.3.5-3ubuntu1 for IPv6 on Ubuntu 17.04, I was finding that on boot I was getting failures with the logged message "no link-local IPv6 address for <ifname>" I found that it took several seconds for the link-local address to be assigned when the interface came up (in this case, the ISP/modem- facing interface), and worked around it with a script that looks at /sbin/ifconfig $IFACE | /bin/fgrep -q 'scopeid 0x20' and loops for a fixed number of times for that to be successful. On looking at /sbin/dhclient-script it appears that it *tries* to do the same thing in # set the link up and wait for ipv6 link local dad to finish ipv6_link_up_and_dad() this code sets out=$(ip -6 -o address show dev "$dev" scope link) then checks it with a case statement inside of a loop for case " $out " in *\ dadfailed\ *) error "$dev: ipv6 dad failed." return 1;; *\ tentative\ *) :;; *) return 0;; esac If there is no link-local address, $out will be empty. The default case is taken, and the loop exits immediately: $ echo "'$out'" ; case " $out " in > *\ dadfailed\ *) > echo "dadfailed" > ;; > *\ tentative\ *) > echo "tentative" > ;; > *) > echo "default" > esac '' default As a result, there is no "wait for link-local address" and when there is no link-local address, dhclient fails later on. Possible Fix: ============= Adding "the missing case" for "no address" case that continues the loop is one possible solution. . case " $out " in . *\ dadfailed\ *) . error "$dev: ipv6 dad failed." . return 1;; . *\ tentative\ *) :;; + " ") + : + ;; . *) return 0;; . esac At least in my situation, this prevents the failure of dhclient due to the link-local address not being "ready" yet. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1718568/+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
