Debian 10升级至11后无特权LXC容器无法通过配置文件分配IP地址

我刚把Debian从10升级到11，结果我的无特权容器现在没法通过配置文件分配IP地址了，具体情况如下：

容器配置文件内容 #

容器配置文件路径为/var/lib/lxc/DNS/config，内容如下：

# Template used to create this container: /usr/share/lxc/templates/lxc-download

# Parameters passed to the template:

# Template script checksum (SHA-1): 273c51343604eb85f7e294c8da0a5eb769d648f3

# For additional config options, please look at lxc.container.conf(5)

# Uncomment the following line to support nesting containers:

#lxc.include = /usr/share/lxc/config/nesting.conf

# (Be aware this has security implications)

# Distribution configuration

lxc.include = /usr/share/lxc/config/common.conf

lxc.include = /usr/share/lxc/config/userns.conf

lxc.arch = linux64

# Container specific configuration

lxc.apparmor.profile = unconfined

lxc.idmap = u 0 1258512 65536

lxc.idmap = g 0 1258512 65536

lxc.rootfs.path = dir:/var/lib/lxc/DNS/rootfs

lxc.uts.name = DNS

lxc.start.auto = 1

# Network configuration

lxc.net.0.type = veth

lxc.net.0.link = br.lxc

lxc.net.0.flags = up

lxc.net.0.ipv4.address = 192.168.5.2/24

lxc.net.0.ipv4.gateway = 192.168.5.1

lxc.net.0.hwaddr = DC:A6:32:xx:xx:xx

问题现象 #

执行lxc-info看不到IP，看起来配置文件直接被忽略了：

Name:           DNS
State:          RUNNING
PID:            32190
Link:           vethXPVwwA
TX bytes:      2.39 KiB
RX bytes:      778 bytes
Total bytes:   3.15 KiB

升级后容器内部还莫名出现了几个陌生的网络接口：

# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
2: gre0@NONE: <NOARP> mtu 1476 qdisc noop state DOWN group default qlen 1000
link/gre 0.0.0.0 brd 0.0.0.0
3: gretap0@NONE: <BROADCAST,MULTICAST> mtu 1462 qdisc noop state DOWN group default qlen 1000
link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
4: erspan0@NONE: <BROADCAST,MULTICAST> mtu 1450 qdisc noop state DOWN group default qlen 1000
link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
5: eth0@if46: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether dc:a6:32:xx:xx:xx brd ff:ff:ff:ff:ff:ff link-netnsid 0

我想手动给接口分配IP，但容器里既没有systemd-networking，连/etc/network/interfaces都找不到：

# ls -l /etc/network/interfaces
ls: cannot access '/etc/network/interfaces': No such file or directory

容器本身运行是正常的，所有服务都启动了，但就是网络没有IP。手动在容器里给veth分配IP后，主机上对应的veth接口也看不到这个IP。

另外，我手动给容器添加路由和IP后，dmesg里冒出了大量这样的日志：

[13417.386863] WARNING (unknown src intf):IN=br.lxc OUT= MAC=ff:ff:ff:ff:ff:ff:dc:a6:32:xx:xx:xx:xx:00 SRC=0.0.0.0 DST=255.255.255.255 LEN=314 TOS=0x00 PREC=0xC0 TTL=64 ID=0 PROTO=UDP SPT=68 DPT=67 LEN=294

但实际上这个接口根本不是未知的，主机明确知道它的存在，而且有对应的路由：

50: br.lxc: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 5e:82:0a:99:4b:fc brd ff:ff:ff:ff:ff:ff
192.168.5.0/24 dev br.lxc proto kernel scope link src 192.168.5.1

我到底漏掉了什么？为什么veth接口就是没有IP？真的急需帮助解决这个问题。

备注：内容来源于stack exchange，提问作者user609425