Re: [PATCH 0/2] vfs/security/NFS/btrfs: clean up and fix LSM option handling

From: Ondrej Mosnacek <omosnace@redhat.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linux Security Module list 
	<linux-security-module@vger.kernel.org>,
	SElinux list <selinux@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org,
	linux-nfs <linux-nfs@vger.kernel.org>,
	linux-btrfs@vger.kernel.org, Paul Moore <paul@paul-moore.com>,
	Olga Kornievskaia <aglo@umich.edu>,
	David Howells <dhowells@redhat.com>,
	Stephen Smalley <stephen.smalley.work@gmail.com>
Subject: Re: [PATCH 0/2] vfs/security/NFS/btrfs: clean up and fix LSM option handling
Date: Fri, 9 Apr 2021 19:39:02 +0200	[thread overview]
Message-ID: <CAFqZXNuhog5YfaG9CBVmZ+C3mSzAEgZkSC-mrQGOD4vyLEz4Xw@mail.gmail.com> (raw)
In-Reply-To: <YHBITqlAfOk8IV5w@zeniv-ca.linux.org.uk>

On Fri, Apr 9, 2021 at 2:28 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Fri, Apr 09, 2021 at 01:12:52PM +0200, Ondrej Mosnacek wrote:
> > This series attempts to clean up part of the mess that has grown around
> > the LSM mount option handling across different subsystems.
>
> I would not describe growing another FS_... flag

Why is that necessarily a bad thing?

> *AND* spreading the
> FS_BINARY_MOUNTDATA further, with rather weird semantics at that,
> as a cleanup of any sort.

How is this spreading it further? The patches remove one (rather bad)
use of it in SELinux and somewhat reduce its use in btrfs.

Hold on... actually I just realized that with FS_HANDLES_LSM_OPTS it
is possible to do btrfs without FS_BINARY_MOUNTDATA and also eliminate
the need for the workaround in vfs_parse_fs_param() (i.e. [2]).

Basically instead of setting FS_BINARY_MOUNTDATA | FS_HANDLES_LSM_OPTS
in btrfs_fs_type and neither in btrfs_root_fs_type, it is enough to
set neither in btrfs_fs_type and only FS_HANDLES_LSM_OPTS in
btrfs_root_fs_type. The security opts are then applied in the outer
vfs_get_tree() call instead of the inner one, but the net effect is
the same.

That should pretty much do away with both the non-legit users of
FS_BINARY_MOUNTDATA (selinux_set_mnt_opts() and btrfs). All the rest
seem to be in line with the semantic.

Would [something like] the above stand any chance of getting your approval?

[2] https://lore.kernel.org/selinux/20210401065403.GA1363493@infradead.org/T/

--
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.