On Mon, Jun 28, 2021 at 09:14:10PM +0800, yang.yang29@xxxxxxxxxx wrote: > > I'm confused about what the actual problem is tbh: > > > > root@h3:~# stat -c "%A %a %n" /proc/sys/net/ipv4/ip_forward > > -rw-r--r-- 644 /proc/sys/net/ipv4/ip_forward > > > > root@h3:~# echo 0 > /proc/sys/net/ipv4/ip_forward > > > > root@h3:~# cat /proc/sys/net/ipv4/ip_forward > > 0 > > > > root@h3:~# cat /proc/self/uid_map > > 0 100000 1000000000 > > Sorry to describe too simple. More specific: > 1.Run dockerd with user namespace enbled > echo dockremap:296608:65536 > /etc/subuid;echo dockremap:296608:65536 > /etc/subgid > dockerd ... --userns-remap=default > 2.Create a container > docker run -it ... sh > > Then root account in the container is 296608 account in the host: > / # cat /proc/self/uid_map > 0 296608 65536 > > In the container, /proc/sys/net/ipv4/ip_forward's owner is root, but root can't modify it: > / # whoami > root > / # ls -l /proc/sys/net/ipv4/ip_forward > -rw-r--r-- 1 root root 0 Jun 28 12:46 /proc/sys/net/ipv4/ip_forward > / # cat /proc/sys/net/ipv4/ip_forward > 1 > / # echo 0 > /proc/sys/net/ipv4/ip_forward > sh: can't create /proc/sys/net/ipv4/ip_forward: Permission denied > > And /proc/sys/net/ipv4/ip_forward has considerd about net namespace, > see net_ctl_set_ownership() in net\sysctl_net.c. > So root in container should be able to modify /proc/sys/net/ipv4/ip_forward. > This doesn't impact /proc/sys/net/ipv4/ip_forward in the host or other container with other net namespace. Sorry to resort to "It works on my machine" but I just pasted you the exact same setup and showed you that this works as expected. So the reason here is likely that you're lacking capabilities specifically CAP_NET_ADMIN. If I reproduce with your setup I can't even create a dummy network device: / # ip link add bla type dummy ip: RTNETLINK answers: Operation not permitted whereas on any unprivileged container that reatins CAP_NET_ADMIN that just works fine. So I would think that if you retain CAP_NET_ADMIN things will work out just fine. Take a look at net_ctl_permissions. There's really no reason to drop CAP_NET_ADMIN in a network namespace that is owned by a non-initial user namespace anyway. Christian
