Re: Nested NTFS volumes within Windows SMB share may result in inode collisions in linux client

[Andrew Walker <awalker@ixsystems.com>]

On Thu, Mar 2, 2023 at 1:32 PM Tom Talpey <tom@talpey.com> wrote:
>
> On 3/2/2023 2:23 PM, Steve French wrote:
> >> Why isn't this behavior simply the default?
> >
> > Without persisted inode numbers (UniqueId) it would cause problems
> > with hardlinks (ie mounting with noserverino).  We could try a trick
> > of hashing them with the volume id if we could detect the transition
> > to a different volume (as original thread was discussing) -
> > fortunately in Linux you have to walk a path component by component so
> > might be possible to spot these more easily.
>
> Well yeah, it can't be a random assignment, and the fileid is only
> unique within the scope of a volumeid. Blindly using the server's
> fileid as a client inode without checking for a volume crossing is
> a client protocol violation, right?
>
>
> > On Thu, Mar 2, 2023 at 1:19 PM Tom Talpey <tom@talpey.com> wrote:
> >>
> >> On 3/1/2023 8:49 PM, Steve French wrote:
> >>> I would expect when the inode collision is noted that
> >>> "cifs_autodisable_serverino()" will get called in the Linux client and
> >>> you should see: "Autodisabling the user of server inode numbers on
> >>> ..."
> >>> "Consider mounting with noserverino to silence this message"
> >>
> >> Why isn't this behavior simply the default? It's going to be
> >> data corruption (sev 1 issue) if the inode number is the same
> >> for two different fileid's, so this seems entirely backwards.
> >>
> >> Also, the words "to silence this message" really don't convey
> >> the severity of the situation.
> >>
> >> Tom.
> >
> >
> >

Just glancing briefly at the kernel NFS client, it appears there is
dynamic handling for crossing mountpoints:
```
/*
 * nfs_d_automount - Handle crossing a mountpoint on the server
 * @path - The mountpoint
 *
 * When we encounter a mountpoint on the server, we want to set up
 * a mountpoint on the client too, to prevent inode numbers from
 * colliding, and to allow "df" to work properly.
 * On NFSv4, we also want to allow for the fact that different
 * filesystems may be migrated to different servers in a failover
 * situation, and that different filesystems may want to use
 * different security flavours.
 */
struct vfsmount *nfs_d_automount(struct path *path)
{
```
c.f. fs/nfs/namespace.c

and

```
                } else if (S_ISDIR(inode->i_mode)) {
                        inode->i_op =
NFS_SB(sb)->nfs_client->rpc_ops->dir_inode_ops;
                        inode->i_fop = &nfs_dir_operations;
                        inode->i_data.a_ops = &nfs_dir_aops;
                        nfs_inode_init_dir(nfsi);
                        /* Deal with crossing mountpoints */
                        if (fattr->valid & NFS_ATTR_FATTR_MOUNTPOINT ||
                                        fattr->valid &
NFS_ATTR_FATTR_V4_REFERRAL) {
                                if (fattr->valid & NFS_ATTR_FATTR_V4_REFERRAL)
                                        inode->i_op =
&nfs_referral_inode_operations;
                                else
                                        inode->i_op =
&nfs_mountpoint_inode_operations;
                                inode->i_fop = NULL;
                                inode->i_flags |= S_AUTOMOUNT;
                        }
```

in fs/nfs/inode.c

Andrew