linux-kernel - Re: linux-next: manual merge of the selinux tree with the vfs tree

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Date:   Mon, 3 Dec 2018 21:56:39 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Ondrej Mosnacek <omosnace@...hat.com>
Cc:     Paul Moore <paul@...l-moore.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-next@...r.kernel.org,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>, selinux@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: linux-next: manual merge of the selinux tree with the vfs tree

On Mon, Dec 03, 2018 at 11:12:59AM +0100, Ondrej Mosnacek wrote:

> I think I figured out what's the problem. NFS still creates the
> submount via the old vfs_submount() call, which calls
> vfs_kern_mount(), which creates an fs_context with
> FS_CONTEXT_FOR_USER_MOUNT because FS_CONTEXT_FOR_SUBMOUNT needs the
> mountpoint dentry reference and there is currently no way to pass that
> to vfs_kern_mount(). This is further complicated by the fact that
> vfs_submount() accepts only a const reference to the mountpoint, while
> vfs_new_fs_context() expects a non-const one...
> 
> I think all users of the old vfs_submount call should be converted to
> the new API before the VFS changes are merged into mainline, otherwise
> they will break the SELinux submount fix. We could work around it in
> the SELinux hook by checking the fc->sb_flags[_mask] for SB_SUBMOUNT,
> but I guess that would be a hack.

Could you take a look at vfs.git#Q28?  There's still a massive reshuffling
going on, so there will be more branches; this one is the latest at the
moment.

I really hate the situation around sb_clone_mnt_opts/sb_set_mnt_opts and
I'm none too fond of the way fs_context_validate is done, so there will
be quite a bit of LSM tweaking.  If we are doing that, let's do it
right...