RE: [CFT][PATCH] proc: Update /proc/net to point at the accessing threads network namespace

David Laight
2022-10-04T08:53:57Z

From: Eric W. Biederman
> Sent: 03 October 2022 18:07
>
> David Laight <David.Laight@ACULAB.COM> writes:
>
> > From: Eric W. Biederman
...
> > Part of the problem is that changing the net namespace isn't
> > enough, you also have to remount /sys - which isn't entirely
> > trivial.
>
> Yes. That is actually a much more maintainable model. But it is still
> imperfect. I was thinking about the proc/net directories when
> I made my comment. Unlike proc where we have task ids there is nothing
> in /proc that can do anything.
>
> > It might be possibly to mount a network namespace version
> > of /sys on a different mountpoint - I've not tried very
> > hard to do that.
>
> It is a bug if that doesn't work.

The difficultly is picking the 'spell'.
I think you need to run mount after switching to the namespace.
But you don't want the unshare() that 'ip netns exec' does.
So I think it needs a silly wrapper program.

> >> > Notwithstanding the apparmor issues, /proc/net could actuall be
> >> > a symlink to (say) /proc/net_namespaces/namespace_name with
> >> > readlink returning the name based on the threads actual namespace.
> >>
> >> There really aren't good names for namespaces at the kernel level. As
> >> one of their use cases is to make process migration possible between
> >> machines. So any kernel level name would need to be migrated as well.
> >> So those kernel level names would need a name in another namespace,
> >> or an extra namespace would have to be created for those names.
> >
> > Network namespaces do seem to have names.
> > Although I gave up working out how to change to a named network
> > namespace from within the kernel (especially in a non-GPL module).
>
> Network namespaces have mount points. The mount points have names.
>
> It is just a matter of finding the right filesystem and calling
> sys_rename().

I wanted to lookup a net namespace by name - so I could create
a kernel socket in a namespace specified in configuration data.
Not change the name of a namespace.

I ended up only giving a few options - basically saving the
namespace of code that called into the driver.
(Harder in a non-gpl driver since you can't directly hold/release
the namespace itself - fortunately you can create a socket!)

David

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