CephFS Client Capabilities

Use Ceph authentication capabilities to restrict your filesystem clients to the lowest possible level of authority needed.

Note

Path restriction and layout modification restriction are new features in the Jewel release of Ceph.

Path restriction

By default, clients are not restricted in what paths they are allowed to mount. Further, when clients mount a subdirectory, e.g., /home/user, the MDS does not by default verify that subsequent operations are ‘locked’ within that directory.

To restrict clients to only mount and work within a certain directory, use path-based MDS authentication capabilities.

Syntax

To grant rw access to the specified directory only, we mention the specified directory while creating key for a client following the undermentioned syntax.

./ceph auth get-or-create client.*client_name* mon 'allow r' mds 'allow r, allow rw path=/*specified_directory*' osd 'allow rw pool=data'

for example, to restrict client foo to writing only in the bar directory, we will use:

./ceph auth get-or-create client.foo mon 'allow r' mds 'allow r, allow rw path=/bar' osd 'allow rw pool=data'

To completely restrict the client to the bar directory, omit the unqualified “allow r” clause:

./ceph auth get-or-create client.foo mon 'allow r' mds 'allow rw path=/bar' osd 'allow rw pool=data'

Note that if a client’s read access is restricted to a path, they will only be able to mount the filesystem when specifying a readable path in the mount command (see below).

See User Management - Add a User to a Keyring. for additional details on user management

To restrict a client to the specfied sub-directory only, we mention the specified directory while mounting following the undermentioned syntax.

./ceph-fuse -n client.*client_name* *mount_path* -r *directory_to_be_mounted*

for example, to restrict client foo to mnt/bar directory, we will use.

./ceph-fuse -n client.foo mnt -r /bar

Free space reporting

By default, when a client is mounting a sub-directory, the used space (df) will be calculated from the quota on that sub-directory, rather than reporting the overall amount of space used on the cluster.

If you would like the client to report the overall usage of the filesystem, and not just the quota usage on the sub-directory mounted, then set the following config option on the client:

client quota df = false

If quotas are not enabled, or no quota is set on the sub-directory mounted, then the overall usage of the filesystem will be reported irrespective of the value of this setting.

OSD restriction

To prevent clients from writing or reading data to pools other than those in use for CephFS, set an OSD authentication capability that restricts access to the CephFS data pool(s):

client.0
    key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
    caps: [mds] allow rw
    caps: [mon] allow r
    caps: [osd] allow rw pool=data1, allow rw pool=data2

Note

Without a corresponding MDS path restriction, the OSD capabilities above do not restrict file deletions outside of the data1 and data2 pools.

You may also restrict clients from writing data by using ‘r’ instead of ‘rw’ in OSD capabilities. This does not affect the ability of the client to update filesystem metadata for these files, but it will prevent them from persistently writing data in a way that would be visible to other clients.

Layout modification restriction

To prevent clients from modifying the data pool used for files or directories, use the ‘p’ modifier in MDS authentication capabilities.

For example, in the following snippet client.0 can modify the pool used for files, but client.1 cannot.

client.0
    key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
    caps: [mds] allow rwp
    caps: [mon] allow r
    caps: [osd] allow rw pool=data

client.1
    key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
    caps: [mds] allow rw
    caps: [mon] allow r
    caps: [osd] allow rw pool=data