Cloud Data Access
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Security Model and Operations on S3

The security and permissions model of Amazon S3 is very different from this of a UNIX-style filesystem: on Amazon S3, operations which query or manipulate permissions are generally unsupported. Operations to which this applies include: chgrp, chmod, chown, getfacl, and setfacl. The related attribute commands getfattr andsetfattr are also unavailable. In addition, operations which try to preserve permissions (for example fs -put -p) do not preserve permissions.

Although these operations are unsupported, filesystem commands which list permission and user/group details usually simulate these details. As a consequence, when interacting with read-only object stores, the permissions found in "list" and "stat" commands may indicate that the user has write access — when in fact he does't.

Amazon S3 has a permissions model of its own. This model can be manipulated through store-specific tooling. Be aware that some of the permissions which can be set — such as write-only paths, or various permissions on the root path — may be incompatible with the S3A client. It expects full read and write access to the entire bucket with trying to write data, and may fail if it does not have these permissions.

As an example of how permissions are simulated, here is a listing of Amazon's public, read-only bucket of Landsat images:

$ hadoop fs -ls s3a://landsat-pds/
Found 10 items
drwxrwxrwx   - mapred          0 2016-09-26 12:16 s3a://landsat-pds/L8
-rw-rw-rw-   1 mapred      23764 2015-01-28 18:13 s3a://landsat-pds/index.html
drwxrwxrwx   - mapred          0 2016-09-26 12:16 s3a://landsat-pds/landsat-pds_stats
-rw-rw-rw-   1 mapred        105 2016-08-19 18:12 s3a://landsat-pds/robots.txt
-rw-rw-rw-   1 mapred         38 2016-09-26 12:16 s3a://landsat-pds/run_info.json
drwxrwxrwx   - mapred          0 2016-09-26 12:16 s3a://landsat-pds/runs
-rw-rw-rw-   1 mapred   27458808 2016-09-26 12:16 s3a://landsat-pds/scene_list.gz
drwxrwxrwx   - mapred          0 2016-09-26 12:16 s3a://landsat-pds/tarq
drwxrwxrwx   - mapred          0 2016-09-26 12:16 s3a://landsat-pds/tarq_corrupt
drwxrwxrwx   - mapred          0 2016-09-26 12:16 s3a://landsat-pds/test

As you can see:

  • All files are listed as having full read/write permissions.

  • All directories appear to have full rwx permissions.

  • The replication count of all files is "1".

  • The owner of all files and directories is declared to be the current user (mapred).

  • The timestamp of all directories is actually that of the time the -ls operation was executed. This is because these directories are not actual objects in the store; they are simulated directories based on the existence of objects under their paths.

When an attempt is made to delete one of the files, the operation fails — despite the permissions shown by the ls command:

$ hadoop fs -rm s3a://landsat-pds/scene_list.gz
rm: s3a://landsat-pds/scene_list.gz: delete on s3a://landsat-pds/scene_list.gz: Access Denied (Service: Amazon S3;
  Status Code: 403; Error Code: AccessDenied; Request ID: 1EF98D5957BCAB3D),
  S3 Extended Request ID: wi3veOXFuFqWBUCJgV3Z+NQVj9gWgZVdXlPU4KBbYMsw/gA+hyhRXcaQ+PogOsDgHh31HlTCebQ=

This demonstrates that the listed permissions cannot be taken as evidence of write access; only object manipulation can determine this.