Date: Wed, 9 Mar 2016 09:25:05 -0600
From: Seth Forshee <seth.forshee@canonical.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Richard Weinberger <richard.weinberger@gmail.com>,
        Austin S Hemmelgarn <ahferroin7@gmail.com>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-bcache@vger.kernel.org, dm-devel@redhat.com,
        linux-raid@vger.kernel.org, linux-mtd@lists.infradead.org,
        Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
        fuse-devel <fuse-devel@lists.sourceforge.net>,
        LSM <linux-security-module@vger.kernel.org>, selinux@tycho.nsa.gov
Subject: Re: [PATCH RESEND v2 16/18] fuse: Support fuse filesystems outside
 of init_user_ns
Message-ID: <20160309152505.GA28779@ubuntu-hedt>
References: <1451930639-94331-1-git-send-email-seth.forshee@canonical.com>
 <1451930639-94331-17-git-send-email-seth.forshee@canonical.com>
 <20160309112923.GF8655@tucsk>
 <20160309141840.GC23399@ubuntu-xps13>
 <CAJfpegv5JmB15yHpjYxVeOYdWWkoLMftr9-e_iS93Y_7m=t4Zw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAJfpegv5JmB15yHpjYxVeOYdWWkoLMftr9-e_iS93Y_7m=t4Zw@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1831
Lines: 42

On Wed, Mar 09, 2016 at 03:48:22PM +0100, Miklos Szeredi wrote:
> On Wed, Mar 9, 2016 at 3:18 PM, Seth Forshee <seth.forshee@canonical.com> wrote:
> > On Wed, Mar 09, 2016 at 12:29:23PM +0100, Miklos Szeredi wrote:
> >> On Mon, Jan 04, 2016 at 12:03:55PM -0600, Seth Forshee wrote:
> 
> >> > -static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev)
> >> > +static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev,
> >> > +                     struct user_namespace *user_ns)
> >> >  {
> >> >     char *p;
> >> >     memset(d, 0, sizeof(struct fuse_mount_data));
> >> >     d->max_read = ~0;
> >> >     d->blksize = FUSE_DEFAULT_BLKSIZE;
> >> > +   d->user_id = make_kuid(user_ns, 0);
> >> > +   d->group_id = make_kgid(user_ns, 0);
> >>
> >> It is true that if "user_id=" or "group_id" options were omitted we used the
> >> zero uid/gid values.  However, this isn't actually used by anybody AFAIK, and
> >> generalizing it for userns doesn't seem to make much sense.
> >>
> >> So I suggest we that we instead return an error if mounting from a userns AND
> >> neither "allow_other" nor both "user_id" and "group_id" are specified.
> >
> > But those are also used for ownership of the connection files in
> > fusectl. In an allow_other mount shouldn't those files by owned by
> > namespace root and not global root?
> 
> Yes.
> 
> Can't we use current_cred()->uid/gid? Or fsuid/fsgid maybe?

That would be a departure from the current behavior in the !allow_other
case for unprivileged users. Since those mounts are done by an suid
helper all of those ids would be root in the userns, wouldn't they?

> When we have true unprivileged mounts, the user_id/group_id options
> become redundant anyway and we can just use the current credentials.

True, but we don't yet have that.

Thanks,
Seth