linux-kernel - Re: What do LSMs *actually* need for checks on notifications?

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Message-ID: <25045.1560339786@warthog.procyon.org.uk>
Date:   Wed, 12 Jun 2019 12:43:06 +0100
From:   David Howells <dhowells@...hat.com>
To:     Stephen Smalley <sds@...ho.nsa.gov>
Cc:     dhowells@...hat.com, Casey Schaufler <casey@...aufler-ca.com>,
        Andy Lutomirski <luto@...nel.org>, viro@...iv.linux.org.uk,
        linux-usb@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: What do LSMs *actually* need for checks on notifications?

Stephen Smalley <sds@...ho.nsa.gov> wrote:

> >   (6) The security attributes of all the objects between the object in (5)
> >       and the object in (4), assuming we work from (5) towards (4) if the
> >       two aren't coincident (WATCH_INFO_RECURSIVE).
> 
> Does this apply to anything other than mount notifications?

Not at the moment.  I'm considering making it such that you can make a watch
on a keyring get automatically propagated to keys that get added to the
keyring (and removed upon unlink) - the idea being that there is no 'single
parent path' concept for a keyring as there is for a directory.

I'm also pondering the idea of making it possible to have superblock watches
automatically propagated to superblocks created by automount points on the
watched superblock.

> And for mount notifications, isn't the notification actually for a change to
> the mount namespace, not a change to any file?

Yes.

> Hence, the real "object" for events that trigger mount notifications is the
> mount namespace, right?

Um... arguably.  Would that mean that that would need a label from somewhere?

> The watched path is just a way of identifying a subtree of the mount
> namespace for notifications - it isn't the real object being watched.

I like that argument.

Thanks,
David