linux-kernel - Re: [PATCH 3/4] proc: Point /proc/net at /proc/thread-self/net instead of /proc/self/net

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Date:   Thu, 29 Sep 2022 20:00:08 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     David Laight <David.Laight@...lab.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH 3/4] proc: Point /proc/net at /proc/thread-self/net
 instead of /proc/self/net

On Thu, Sep 29, 2022 at 07:50:36PM +0100, Al Viro wrote:
> >   https://lore.kernel.org/all/CADDKRnDD_W5yJLo2otWXH8oEgmGdMP0N_p7wenBQbh17xKGZJg@mail.gmail.com/
> > 
> > in case anybody cares.
> > 
> > I wonder if the fix is to replace the symlink with a hardcoded lookup
> > (ie basically make it *act* like a hardlink - we don't really support
> > hardlinked directories, but we could basically fake the lookup in
> > proc). Since the problem was AppArmor reacting to the name in the
> > symlink.
> > 
> > Al added the participants so that he can say "hell no".
> 
> What do you mean?  Lookup on "net" in /proc returning what, exactly?
> What would that dentry have for ->d_parent?

Looking at that thread, it seems that <censored> "policy" would not be
satisfied with anything other than /proc/*/task/*/net being seen
as /proc/<something>/net.  As in "cd there and /bin/pwd will tell you
tha you are in /proc/<some number>/net".

Which is insane, especially since the entire problem is due to wanting
that directory to be different for different threads...