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From: David Howells <dhowells@redhat.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: dhowells@redhat.com, Al Viro <viro@zeniv.linux.org.uk>,
	Casey Schaufler <casey@schaufler-ca.com>,
	raven@themaw.net, Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	linux-block@vger.kernel.org, keyrings@vger.kernel.org,
	LSM List <linux-security-module@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
Date: Tue, 04 Jun 2019 21:39:38 +0100
Message-ID: <1207.1559680778@warthog.procyon.org.uk> (raw)
In-Reply-To: <CALCETrWzDR=Ap8NQ5-YrVhXCEBgr+hwpjw9fBn0m2NkZzZ7XLQ@mail.gmail.com>

Andy Lutomirski <luto@kernel.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.

I'm not sure of the need, and I particularly don't like trying to make
indirect destruction events (mount destruction keyed on fput, for instance)
carry the creds of the triggerer.  Indeed, the trigger can come from all sorts
of places - including af_unix queue destruction, someone poking around in
procfs, a variety of processes fputting simultaneously.  Only one of them can
win, and the LSM needs to handle *all* the possibilities.

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.

> This seems like the wrong approach.  If an LSM wants to prevent covert
> communication from, say, mount actions, then it shouldn't allow the
> watch to be set up in the first place.

Yeah, I can agree to that.  Casey?

David

  parent reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-04 16:34 David Howells
2019-06-04 16:35 ` [PATCH 1/8] security: Override creds in __fput() with last fputter's creds " David Howells
2019-06-04 18:15   ` Andy Lutomirski
2019-06-04 16:35 ` [PATCH 2/8] General notification queue with user mmap()'able ring buffer " David Howells
2019-06-04 16:35 ` [PATCH 3/8] keys: Add a notification facility " David Howells
2019-06-04 16:35 ` [PATCH 4/8] vfs: Add a mount-notification " David Howells
2019-06-04 16:35 ` [PATCH 5/8] vfs: Add superblock notifications " David Howells
2019-06-04 16:36 ` [PATCH 6/8] fsinfo: Export superblock notification counter " David Howells
2019-06-04 16:36 ` [PATCH 7/8] block: Add block layer notifications " David Howells
2019-06-04 16:36 ` [PATCH 8/8] Add sample notification program " David Howells
2019-06-04 17:43 ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications " Andy Lutomirski
2019-06-04 20:31   ` Casey Schaufler
2019-06-04 21:05     ` Andy Lutomirski
2019-06-04 22:03       ` Casey Schaufler
2019-06-05  8:41   ` David Howells
2019-06-05 14:50     ` Casey Schaufler
2019-06-05 16:04       ` Andy Lutomirski
2019-06-05 17:01         ` Casey Schaufler
2019-06-05 17:47           ` Andy Lutomirski
2019-06-05 18:12             ` Casey Schaufler
2019-06-05 18:25             ` Stephen Smalley
2019-06-05 19:28               ` Greg KH
2019-06-05 21:01                 ` Stephen Smalley
2019-06-05 16:56     ` Rational model for UID based controls David Howells
2019-06-05 17:40       ` Casey Schaufler
2019-06-05 21:06       ` David Howells
2019-06-05 17:21     ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
2019-06-04 20:39 ` David Howells [this message]
2019-06-04 20:57   ` Andy Lutomirski
     [not found]     ` <CAB9W1A0AgMYOwGx9c-TmAt=1O6Bjsr2P3Nhd=2+QV39dgw0CrA@mail.gmail.com>
2019-06-05  4:19       ` Andy Lutomirski
2019-06-05 13:47         ` Stephen Smalley
2019-06-04 21:11   ` Casey Schaufler

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