On Thu, Aug 29, 2024 at 2:17 PM Aleksandr Mikhalitsyn
<aleksandr.mikhalitsyn@xxxxxxxxxxxxx> wrote:
>
> On Thu, Aug 29, 2024 at 2:08 PM Christian Brauner <brauner@xxxxxxxxxx> wrote:
> >
> > On Thu, Aug 29, 2024 at 10:24:42AM GMT, Miklos Szeredi wrote:
> > > On Thu, 18 Jul 2024 at 21:12, Aleksandr Mikhalitsyn
> > > <aleksandr.mikhalitsyn@xxxxxxxxxxxxx> wrote:
> > >
> > > > This was a first Christian's idea when he originally proposed a
> > > > patchset for cephfs [2]. The problem with this
> > > > approach is that we don't have an idmapping provided in all
> > > > inode_operations, we only have it where it is supposed to be.
> > > > To workaround that, Christian suggested applying a mapping only when
> > > > we have mnt_idmap, but if not just leave uid/gid as it is.
> > > > This, of course, leads to inconsistencies between different
> > > > inode_operations, for example ->lookup (idmapping is not applied) and
> > > > ->symlink (idmapping is applied).
> > > > This inconsistency, really, is not a big deal usually, but... what if
> > > > a server does UID/GID-based permission checks? Then it is a problem,
> > > > obviously.
> > >
> > > Is it even sensible to do UID/GID-based permission checks in the
> > > server if idmapping is enabled?
>
> Dear friends,
>
> >
> > It really makes no sense.
>
> +
>
> >
> > >
> > > If not, then we should just somehow disable that configuration (i.e.
> > > by the server having to opt into idmapping), and then we can just use
> > > the in_h.[ugi]d for creates, no?
> >
> > Fwiw, that's what the patchset is doing. It's only supported if the
> > server sets "default_permissions".
>
> Yeah. Thanks, Christian!
>
> That's what we have:
>
> +++ b/fs/fuse/inode.c
> @@ -1345,6 +1345,12 @@ static void process_init_reply(struct
> fuse_mount *fm, struct fuse_args *args,
> fm->sb->s_export_op = &fuse_export_fid_operations;
> if (flags & FUSE_OWNER_UID_GID_EXT)
> fc->owner_uid_gid_ext = 1;
> + if (flags & FUSE_ALLOW_IDMAP) {
> + if (fc->owner_uid_gid_ext && fc->default_permissions)
> + fm->sb->s_iflags &= ~SB_I_NOIDMAP;
> + else
> + ok = false;
> + }
> } else {
> ra_pages = fc->max_read / PAGE_SIZE;
>
> So idmapped mounts can be enabled ONLY if "default_permissions" mode
> is set. At the same time,
> some fuse servers (glusterfs), even when "default_permissions" is set,
> still have some UID/GID-based checks.
> So, they effectively duplicate permission checking logic in the
> userspace. We can not do anything with that, but only
> fix fuse servers to stop doing so. See also my PoC for glusterfs-fuse
> idmapped mounts support:
> https://github.com/mihalicyn/glusterfs/commit/ab3ec2c7cbe22618cba9cc94a52a492b1904d0b2
and yes, latest patchset (v3) is here:
https://lore.kernel.org/all/20240815092429.103356-1-aleksandr.mikhalitsyn@xxxxxxxxxxxxx/#t
>
> Kind regards,
> Alex
