CephFS Client Capabilities

Use Ceph authentication capabilities to restrict your file system clientsto the lowest possible level of authority needed.

Note

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

Note

Using Erasure Coded(EC) pools with CephFS is supported only with theBlueStore Backend. They cannot be used as metadata pools and overwrites mustbe enabled on the data pools.

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 notby default verify that subsequent operationsare ‘locked’ within that directory.

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

Syntax

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

  1. ceph fs authorize *file_system_name* client.*client_name* /*specified_directory* rw

For example, to restrict client foo to writing only in the bar directory of file system cephfs, use

  1. ceph fs authorize cephfs client.foo / r /bar rw
  2.  
  3. results in:
  4.  
  5. client.foo
  6. key: *key*
  7. caps: [mds] allow r, allow rw path=/bar
  8. caps: [mon] allow r
  9. caps: [osd] allow rw tag cephfs data=cephfs_a

To completely restrict the client to the bar directory, omit theroot directory

  1. ceph fs authorize cephfs client.foo /bar rw

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

Supplying all or as the file system name will grant access to everyfile system. Note that it is usually necessary to quote to protect it fromthe shell.

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

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

  1. ./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.

  1. ./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 reportingthe overall amount of space used on the cluster.

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

  1. 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 file system will be reported irrespective ofthe value of this setting.

Layout and Quota restriction (the ‘p’ flag)

To set layouts or quotas, clients require the ‘p’ flag in addition to ‘rw’.This restricts all the attributes that are set by special extended attributeswith a “ceph.” prefix, as well as restricting other means of settingthese fields (such as openc operations with layouts).

For example, in the following snippet client.0 can modify layouts and quotason the file system cephfs_a, but client.1 cannot.

  1. client.0
  2. key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
  3. caps: [mds] allow rwp
  4. caps: [mon] allow r
  5. caps: [osd] allow rw tag cephfs data=cephfs_a
  6.  
  7. client.1
  8. key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
  9. caps: [mds] allow rw
  10. caps: [mon] allow r
  11. caps: [osd] allow rw tag cephfs data=cephfs_a

Snapshot restriction (the ‘s’ flag)

To create or delete snapshots, clients require the ‘s’ flag in addition to ‘rw’.Note that when capability string also contains the ‘p’ flag, the ‘s’ flag mustappear after it (all flags except ‘rw’ must be specified in alphabetical order).

For example, in the following snippet client.0 can create or delete snapshotsin the bar directory of file system cephfs_a.

  1. client.0
  2. key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
  3. caps: [mds] allow rw, allow rws path=/bar
  4. caps: [mon] allow r
  5. caps: [osd] allow rw tag cephfs data=cephfs_a

Network restriction

  1. client.foo
  2. key: *key*
  3. caps: [mds] allow r network 10.0.0.0/8, allow rw path=/bar network 10.0.0.0/8
  4. caps: [mon] allow r network 10.0.0.0/8
  5. caps: [osd] allow rw tag cephfs data=cephfs_a network 10.0.0.0/8

The optional {network/prefix} is a standard network name andprefix length in CIDR notation (e.g., 10.3.0.0/16). If present,the use of this capability is restricted to clients connecting fromthis network.