[ Dropping my previous email from the CC list ]
On Fri, Feb 14 2025, Jeff Layton wrote:
> On Fri, 2025-02-14 at 03:28 +0000, Al Viro wrote:
>> On Fri, Feb 14, 2025 at 02:47:56AM +0000, Al Viro wrote:
>>
>> [snip]
>>
>> > Am I missing something subtle here? Can elen be non-positive at that point?
>>
>> Another fun question: for dentries with name of form _<something>_<inumber>
>> we end up looking at fscrypt_has_encryption_key() not for the parent,
>> but for inode with inumber encoded in dentry name. Fair enough, but...
>> what happens if we run into such dentry in ceph_mdsc_build_path()?
>>
>> There the call of ceph_encode_encrypted_fname() is under
>> if (fscrypt_has_encryption_key(d_inode(parent)))
>>
>> Do we need the keys for both?
>>
>
> That sounds like a bug, but I don't fully recall whether snapshots have
> a special case here for some reason. Let me rephrase Al's question:
>
> If I have a snapshot dir that is prefixed with '_', why does it use a
> different filename encryption key than other snapshot dirs that don't
> start with that character?
>
> My guess here is that this code ought not overwrite "dir" with the
> result of parse_longname(), but I don't recall the significance of a
> snapshot name that starts with '_'.
This bit I _think_ I remember. Imagine this tree structure:
/mnt/ceph
|-- mydir1
|-- mydir2
If you create a snapshot in /mnt/ceph:
mkdir /mnt/ceph/.snap/my-snapshot
you'll see this:
/mnt/ceph
|-- .snap
| |-- my-snapshot
|-- mydir1
| |-- _my-snapshot_1099511627782
|-- mydir2
|-- _my-snapshot_1099511627782
('1099511627782' is the inode number where the snapshot was created.)
So, IIRC, when encrypting the snapshot name (the "my-snapshot" string),
you'll use key from the original inode. That's why we need to handle
snapshot names starting with '_' differently. And why we have a
customized base64 encoding function.
Cheers,
--
Luís
> /* Handle the special case of snapshot names that start with '_' */
> if ((ceph_snap(dir) == CEPH_SNAPDIR) && (name_len > 0) &&
> (iname.name[0] == '_')) {
> dir = parse_longname(parent, iname.name, &name_len);
> if (IS_ERR(dir))
> return PTR_ERR(dir);
> iname.name++; /* skip initial '_' */
> }
> iname.len = name_len;
>
> if (!fscrypt_has_encryption_key(dir)) {
> memcpy(buf, d_name->name, d_name->len);
> elen = d_name->len;
> goto out;
> }
>
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
>
