[Bug 1424143] [NEW] lxc-net should attempt to use ip before ifconfig, not vice-versa

[Steve Beattie]

Public bug reported:

The lxc-net script in /usr/lib/$archtriplet/lxc/lxc-net attempts to use
ifconfig first and then falls back to trying to use ip(8) in the ifup()
and ifdown() shell functions. This behavior should be reversed, as ip
has been preferred over ifconfig for several years now.

As an example of why, lxc-net breaks the network setup within virtualbox
guests. After starting lxc-net, the route table looks like:

  ubuntu at vivid-i386:~$ route -n
  Kernel IP routing table
  Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
  0.0.0.0         10.0.2.2        0.0.0.0         UG    1024   0        0 eth0
  10.0.0.0        0.0.0.0         255.0.0.0       U     0      0        0 lxcbr0
  10.0.2.0        0.0.0.0         255.255.255.0   U     0      0        0 eth0
  169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0

This is despite the following settings in /etc/default/lxc-net:

  LXC_BRIDGE="lxcbr0"
  LXC_ADDR="10.0.3.1"
  LXC_NETMASK="255.255.255.0"
  LXC_NETWORK="10.0.3.0/24"

Switching the order in ifup and ifdown to try using ip first results in
the correct netmask being applied:

  ubuntu at vivid-i386:~$ route -n
  Kernel IP routing table
  Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
  0.0.0.0         10.0.2.2        0.0.0.0         UG    1024   0        0 eth0
  10.0.2.0        0.0.0.0         255.255.255.0   U     0      0        0 eth0
  10.0.3.0        0.0.0.0         255.255.255.0   U     0      0        0 lxcbr0
  169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0

Looking at sh -x output when running lxc-net manually, it *looks* like
ifconfig is being invoked correctly, so I don't know why it's getting
the netmask wrong:

+ use_iptables_lock=-w
+ iptables -w -L -n
+ [ -d /sys/class/net/lxcbr0 ]
+ brctl addbr lxcbr0
+ echo 1
+ [ ! -d /run/lxc ]
+ ifup lxcbr0 10.0.3.1 255.255.255.0
+ which ifconfig
+ [ 0 = 0 ]
+ ifconfig lxcbr0 10.0.3.1 netmask 255.255.255.0 up
+ return

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: lxc 1.1.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.18.0-13.14-generic 3.18.5
Uname: Linux 3.18.0-13-generic i686
ApportVersion: 2.16.1-0ubuntu2
Architecture: i386
Date: Sat Feb 21 00:13:27 2015
InstallationDate: Installed on 2014-12-12 (70 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Alpha i386 (20141212)
ProcEnviron:
 TERM=screen
 SHELL=/bin/bash
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 XDG_RUNTIME_DIR=<set>
SourcePackage: lxc
UpgradeStatus: No upgrade log present (probably fresh install)
defaults.conf:
 lxc.network.type = veth
 lxc.network.link = lxcbr0
 lxc.network.flags = up
 lxc.network.hwaddr = 00:16:3e:xx:xx:xx
modified.conffile..etc.default.lxc: [modified]
mtime.conffile..etc.default.lxc: 2015-02-20T18:15:56.552501

** Affects: lxc (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: apparmor apport-bug i386 third-party-packages vivid

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Title:
  lxc-net should attempt to use ip before ifconfig, not vice-versa

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