linux-kernel - Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]

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Date:   Tue, 4 Jun 2019 13:57:30 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Casey Schaufler <casey@...aufler-ca.com>, 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: Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]

On Tue, Jun 4, 2019 at 1:39 PM David Howells <dhowells@...hat.com> wrote:
>
> Andy Lutomirski <luto@...nel.org> wrote:
>
> > > Here's a set of patches to add a general variable-length notification queue
> > > concept and to add sources of events for:
> >
> > I asked before and didn't see a response, so I'll ask again.  Why are you
> > paying any attention at all to the creds that generate an event?
>
> Casey responded to you.  It's one of his requirements.
>

It being a "requirement" doesn't make it okay.

> However, the LSMs (or at least SELinux) ignore f_cred and use current_cred()
> when checking permissions.  See selinux_revalidate_file_permission() for
> example - it uses current_cred() not file->f_cred to re-evaluate the perms,
> and the fd might be shared between a number of processes with different creds.

That's a bug.  It's arguably a rather severe bug.  If I ever get
around to writing the patch I keep thinking of that will warn if we
use creds from invalid contexts, it will warn.

Let's please not repeat this.