[PATCH RESEND v2 16/18] fuse: Support fuse filesystems outside of init_user_ns

[Miklos Szeredi]

On Wed, Mar 9, 2016 at 3:18 PM, Seth Forshee <seth.forshee at 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?

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

Thanks,
Miklos