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CephFS Client Capabilities¶

Use Ceph authentication capabilities to restrict your file system 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.

Note

Using Erasure Coded(EC) pools with CephFS is supported only with the BlueStore Backend. They cannot be used as metadata pools and overwrites must be 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 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 using the following syntax:

ceph fs authorize <fs_name> client.<client_id> <path-in-cephfs> rw

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

ceph fs authorize cephfs_a client.foo / r /bar rw

results in:

client.foo
  key: *key*
  caps: [mds] allow r, allow rw path=/bar
  caps: [mon] allow r
  caps: [osd] allow rw tag cephfs data=cephfs_a

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

ceph fs authorize cephfs_a client.foo /bar rw

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

Supplying all or * as the file system name will grant access to every file system. Note that it is usually necessary to quote * to protect it from the 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 specified directory while mounting using the following syntax:

ceph-fuse -n client.<client_id> <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 file system, 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 file system will be reported irrespective of the 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 attributes with a “ceph.” prefix, as well as restricting other means of setting these fields (such as openc operations with layouts).

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

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

client.1
    key: AQAz7EVWygILFRAAdIcuJ12opU/JKyfFmxhuaw==
    caps: [mds] allow rw
    caps: [mon] allow r
    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 must appear after it (all flags except ‘rw’ must be specified in alphabetical order).

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

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

Network restriction¶

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

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

File system Information Restriction¶

If desired, the monitor cluster can present a limited view of the file systems available. In this case, the monitor cluster will only inform clients about file systems specified by the administrator. Other file systems will not be reported and commands affecting them will fail as if the file systems do not exist.

Consider following example. The Ceph cluster has 2 FSs:

$ ceph fs ls
name: cephfs, metadata pool: cephfs_metadata, data pools: [cephfs_data ]
name: cephfs2, metadata pool: cephfs2_metadata, data pools: [cephfs2_data ]

But we authorize client someuser for only one FS:

$ ceph fs authorize cephfs client.someuser / rw
[client.someuser]
    key = AQAmthpf89M+JhAAiHDYQkMiCq3x+J0n9e8REQ==
$ cat ceph.client.someuser.keyring
[client.someuser]
    key = AQAmthpf89M+JhAAiHDYQkMiCq3x+J0n9e8REQ==
    caps mds = "allow rw fsname=cephfs"
    caps mon = "allow r fsname=cephfs"
    caps osd = "allow rw tag cephfs data=cephfs"

And the client can only see the FS that it has authorization for:

$ ceph fs ls -n client.someuser -k ceph.client.someuser.keyring
name: cephfs, metadata pool: cephfs_metadata, data pools: [cephfs_data ]

Standby MDS daemons will always be displayed. Note that the information about restricted MDS daemons and file systems may become available by other means, such as ceph health detail.

MDS communication restriction¶

By default, user applications may communicate with any MDS, whether or not they are allowed to modify data on an associated file system (see Path restriction above). Client’s communication can be restricted to MDS daemons associated with particular file system(s) by adding MDS caps for that particular file system. Consider the following example where the Ceph cluster has 2 FSs:

$ ceph fs ls
name: cephfs, metadata pool: cephfs_metadata, data pools: [cephfs_data ]
name: cephfs2, metadata pool: cephfs2_metadata, data pools: [cephfs2_data ]

Client someuser is authorized only for one FS:

$ ceph fs authorize cephfs client.someuser / rw
[client.someuser]
    key = AQBPSARfg8hCJRAAEegIxjlm7VkHuiuntm6wsA==
$ ceph auth get client.someuser > ceph.client.someuser.keyring
exported keyring for client.someuser
$ cat ceph.client.someuser.keyring
[client.someuser]
    key = AQBPSARfg8hCJRAAEegIxjlm7VkHuiuntm6wsA==
    caps mds = "allow rw fsname=cephfs"
    caps mon = "allow r"
    caps osd = "allow rw tag cephfs data=cephfs"

Mounting cephfs1 with someuser works:

$ sudo ceph-fuse /mnt/cephfs1 -n client.someuser -k ceph.client.someuser.keyring --client-fs=cephfs
ceph-fuse[96634]: starting ceph client
ceph-fuse[96634]: starting fuse
$ mount | grep ceph-fuse
ceph-fuse on /mnt/cephfs1 type fuse.ceph-fuse (rw,nosuid,nodev,relatime,user_id=0,group_id=0,allow_other)

But mounting cephfs2 does not:

$ sudo ceph-fuse /mnt/cephfs2 -n client.someuser -k ceph.client.someuser.keyring --client-fs=cephfs2
ceph-fuse[96599]: starting ceph client
ceph-fuse[96599]: ceph mount failed with (1) Operation not permitted

Root squash¶

The root squash feature is implemented as a safety measure to prevent scenarios such as accidental sudo rm -rf /path. You can enable root_squash mode in MDS caps to disallow clients with uid=0 or gid=0 to perform write access operations – e.g., rm, rmdir, rmsnap, mkdir, mksnap. However, the mode allows the read operations of a root client unlike in other file systems.

Following is an example of enabling root_squash in a filesystem except within ‘/volumes’ directory tree in the filesystem:

$ ceph fs authorize a client.test_a / rw root_squash /volumes rw
$ ceph auth get client.test_a
[client.test_a]
    key = AQBZcDpfEbEUKxAADk14VflBXt71rL9D966mYA==
    caps mds = "allow rw fsname=a root_squash, allow rw fsname=a path=/volumes"
    caps mon = "allow r fsname=a"
    caps osd = "allow rw tag cephfs data=a"