Security

This document describes the following security related features in Alluxio.

  1. User Authentication: Alluxio filesystem will differentiate users accessing the service when the authentication mode is SIMPLE (i.e., alluxio.security.authentication.type=SIMPLE). Alluxio also supports other authentication modes like NOSASL which ignores the difference among users. Having authentication mode to be SIMPLE is required for authorization.
  2. User Authorization: Alluxio filesystem will grant or deny user access based on the requesting user and the POSIX permissions model of the files or directories to access, when alluxio.security.authorization.permission.enabled=true. Note that, authentication cannot be NOSASL as authorization requires user information.
  3. Impersonation: Alluxio supports user impersonation so one user can access Alluxio on the behalf of another user. This can be useful if an Alluxio client is part of a service which provides access to Alluxio for many different users.
  4. Auditing: If alluxio.master.audit.logging.enabled=true, Alluxio file system maintains an audit log for user accesses to file metadata.

See Security specific configuration for different security properties.

Authentication

The authentication protocol is determined by the configuration property alluxio.security.authentication.type, with a default value of SIMPLE.

SIMPLE

Authentication is enabled when the authentication type is SIMPLE.

A client must identify itself with a username to the Alluxio service. If the property alluxio.security.login.username is set on the client, its value will be used as the login user, otherwise, the login user is inferred from the operating system. The provided user information is attached to the corresponding metadata when the client creates directories or files.

NOSASL

Authentication is disabled when the authentication type is NOSASL.

Alluxio service will ignore the user of the client and no user information will be attached to the corresponding metadata when the client creates directories or files.

CUSTOM

Authentication is enabled when the authentication type is CUSTOM.

Alluxio clients retrieves user information via the class provided by the alluxio.security.authentication.custom.provider.class property. The specified class must implement alluxio.security.authentication.AuthenticationProvider.

This mode is currently experimental and should only be used in tests.

Authorization

The Alluxio file system implements a permissions model similar to the POSIX permissions model.

Each file and directory is associated with:

  • An owner, which is the user of the client process to create the file or directory.
  • A group, which is the group fetched from user-groups-mapping service. See User group mapping.
  • Permissions, which consist of three parts:
    • Owner permission defines the access privileges of the file owner
    • Group permission defines the access privileges of the owning group
    • Other permission defines the access privileges of all users that are not in any of above two classes

Each permission has three actions:

  1. read (r)
  2. write (w)
  3. execute (x)

For files:

  • Read permissions are required to read files
  • Write permission are required to write files

For directories:

  • Read permissions are required to list its contents
  • Write permissions are required to create, rename, or delete files or directories under it
  • Execute permissions are required to access a child of the directory

The output of the ls shell command when authorization is enabled is:

./bin/alluxio fs ls /
drwxr-xr-x jack           staff                       24       PERSISTED 11-20-2017 13:24:15:649  DIR /default_tests_files
-rw-r--r-- jack           staff                       80   NOT_PERSISTED 11-20-2017 13:24:15:649 100% /default_tests_files/BASIC_CACHE_PROMOTE_MUST_CACHE

User group mapping

For a given user, the list of groups is determined by a group mapping service, configured by the alluxio.security.group.mapping.class property, with a default implementation of alluxio.security.group.provider.ShellBasedUnixGroupsMapping. This implementation executes the groups shell command to fetch the group memberships of the given user. The user group mapping is cached, with an expiration period configured by the alluxio.security.group.mapping.cache.timeout property, with a default value of 60s. If set to a value of 0, caching is disabled.

Alluxio has super user, a user with special privileges typically needed to administer and maintain the system. The alluxio.security.authorization.permission.supergroup property defines a super group. Any users belong to this group are also super users.

Initialized directory and file permissions

When a file is created, it is initially assigned fully opened permissions of 666 by default. Similarly, a directory is initially assigned with 777 permissions. A umask is applied on the initial permissions; this is configured by the alluxio.security.authorization.permission.umask property, with a default of 022. Without any property modifications, files and directories are created with 644 and 755 permissions respectively.

Update directory and file permission model

The owner, group, and permissions can be changed by two ways:

  1. User application invokes the setAttribute(...) method of FileSystem API or Hadoop API.
  2. CLI command in shell. See chown, chgrp, chmod.

The owner attribute can only be changed by a super user. The group and permission attributes can be changed by a super user or the owner.

Impersonation

Alluxio supports user impersonation in order for a user to access Alluxio on the behalf of another user. This can be useful if an Alluxio client is part of a service which provides access to Alluxio for different users. In this scenario, the Alluxio client is configured to connect to Alluxio servers as a connection user, but act on behalf of, or impersonate, other users. In order to configure Alluxio for impersonation, both client and master configurations are required.

Master Configuration

To enable a particular user to impersonate other users, set the alluxio.master.security.impersonation.<USERNAME>.users property, where <USERNAME> is the name of the connection user.

The property value is a comma-separated list of users that <USERNAME> is allowed to impersonate. The wildcard value * can be used to indicate the user can impersonate any other user. Some examples:

  • alluxio.master.security.impersonation.alluxio_user.users=user1,user2 means the connection user alluxio_user is allowed to impersonate user1 and user2.
  • alluxio.master.security.impersonation.client.users=* means the connection user client is allowed to impersonate any user.

To enable a particular user to impersonate other groups, set the alluxio.master.security.impersonation.<USERNAME>.groups property, where again <USERNAME> is the name of the connection user.

Similar to the above, the value is a comma-separated list of groups and the wildcard value * can be used to indicate all groups. Some examples:

  • alluxio.master.security.impersonation.alluxio_user.groups=group1,group2 means the connection user alluxio_user is allowed to impersonate any users from groups group1 and group2.
  • alluxio.master.security.impersonation.client.groups=* means the connection user client is allowed to impersonate users from any group.

In summary, impersonation of a given user is only enabled if at least one of the two impersonation properties are be set; setting both are allowed for the same user.

Client Configuration

After enabling impersonation on the master for a given user, the client must indicate which user it wants to impersonate. This is configured by the alluxio.security.login.impersonation.username property.

If the property is set to an empty string or _NONE_, impersonation is disabled. If the property is set to _HDFS_USER_, the Alluxio client will impersonate as the same user as the HDFS client when using the Hadoop compatible client. This property can also be set to a particular string to indicate a user name.

Auditing

Alluxio supports audit logging to allow system administrators to track users’ access to file metadata.

The audit log file at master_audit.log contains entries corresponding to file metadata access operations. The format of Alluxio audit log entry is shown in the table below:

keyvalue
succeeded True if the command has succeeded. To succeed, it must also have been allowed.
allowed True if the command has been allowed. Note that a command can still fail even if it has been allowed.
ugi User group information, including username, primary group, and authentication type.
ip Client IP address.
cmd Command issued by the user.
src Path of the source file or directory.
dst Path of the destination file or directory. If not applicable, the value is null.
perm User:group:mask or null if not applicable.

This is similar to the format of HDFS audit log wiki.

To enable Alluxio audit logging, set the JVM property alluxio.master.audit.logging.enabled to true in alluxio-env.sh. See Configuration settings.

Encryption

Service level encryption is not supported yet. Users can encrypt sensitive data at the application level or enable encryption features in the respective under file system, such as HDFS transparent encryption or Linux disk encryption.

Deployment

It is recommended to start Alluxio master and workers under the same user. In the case where there is a user mismatch, file operations may fail because of permission checks.