linux-kernel - Rational model for UID based controls

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Date:   Wed, 05 Jun 2019 17:56:47 +0100
From:   David Howells <dhowells@...hat.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     dhowells@...hat.com, Andy Lutomirski <luto@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>, raven@...maw.net,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-block@...r.kernel.org, keyrings@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Rational model for UID based controls

Casey Schaufler <casey@...aufler-ca.com> wrote:

> YES!

I'm trying to decide if that's fervour or irritation at this point ;-)

> And it would be really great if you put some thought into what
> a rational model would be for UID based controls, too.

I have put some thought into it, but I don't see a single rational model.  It
depends very much on the situation.

In any case, that's what I was referring to when I said I might need to call
inode_permission().  But UIDs don't exist for all filesystems, for example,
and there are no UIDs on superblocks, mount objects or hardware events.

Now, I could see that you ignore UIDs on things like keys and
hardware-triggered events, but how does this interact with things like mount
watches that see directories that have UIDs?

Are you advocating making it such that process B can only see events triggered
by process A if they have the same UID, for example?

David