[PATCH] netns: add /proc/*/net/id symlink

[David Lamparter]

> ... Eric W. Biederman wrote:
> Now it probably needs to be better documented that /proc/*/net/*
> have the same inode number if the network namespace is the
> same, as everyone including myself overlooked this very handy
> existing property.

Eh, so did I. But, yes, very nice.

On Sat, May 21, 2011 at 05:15:38PM -0700, Eric W. Biederman wrote:
> Additionally that solution will work for comparing network namespaces
> that don't happen to have any processes in them at the moment.  Because
> fstat works on file descriptors.

Hm. I have a peeve here. Assume I am a... rogue admin, whatever. I have
root on a router. I create a new network namespace, put a macvlan of
eth0 in it and a macvlan of eth1. I enable ip_forward.

Then I make a mount namespace, bind-mount the net namespace, bind mount
the mount namespace and terminate all processes that reference it (yes
this does work, i just checked [!]).

Now I can use it to bypass all firewall rules, IDS, whatever.

How is any normal admin, monitoring script or whatever else able to
detect this?

> With the /proc/<pid>/ns/net file and bind mounts I have solved the
> deeper problem of how do we get userspace policy into the naming of
> namespaces.  With those files and the setns system call I have solved
> the other problem of what is a good way to refer to namespaces without
> assuming a global name.  So once those changes are merged I expect there
> to be much less pressure to misuse any kind of identifier we can have.
> 
> And if we only make the guarantee about inode consistency for the
> /proc/<pid>/ns/FILE files I don't expect it will make maintenance
> of procfs any harder than it already is.


-David