[PATCH 0/2] Fix /proc/net in presence of net namespaces

[Pavel Emelyanov <xemul@openvz.org>]

Current /proc/net is done with so called "shadows", but current
implementation is broken and has little chances to get fixed.

The problem is that dentries subtree of /proc/net directory has
fancy revalidation rules to make processes living in different
net namespaces see different entries in /proc/net subtree, but
currently, tasks see in the /proc/net subdir the contents of any
other namespace, depending on who opened the file first.

The proposed fix is to turn /proc/net into a symlink, which behaves
similar to /proc/self link - it points to .netns/<id> directory 
where the <id> is the id of net namespace, current task lives in.

# ls -l /proc/net
lrwxrwxrwx  1 root root 8 Feb 28 18:38 /proc/net -> .netns/0

The /proc/.netns dir contains subtrees for all the namespaces in 
the system:

# ls -l /proc/.netns/
total 0
dr-xr-xr-x  5 root root 0 Feb 28 18:39 0
dr-xr-xr-x  3 root root 0 Feb 28 18:39 1

To provide some security each /proc/.netns/<id> directory allows
access to tasks that live in the owning namespace only (with the
exception, that init_net tasks can see everything).

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>