Directory/File Access Permissions for COPY and Generic File Access Functions

All,

The attached patch for review implements a directory permission system that
allows for providing a directory read/write capability to directories for
COPY TO/FROM and Generic File Access Functions to non-superusers. This is
not a complete solution as it does not currently contain documentation or
regression tests. Though it is my hopes to get some feedback as I am sure
there are some aspects of it that need to be reworked. So I thought I'd
put it out there for comments/review.

The approach taken is to create "directory aliases" that have a unique name
and path, as well as an associated ACL list. A superuser can create a new
alias to any directory on the system and then provide READ or WRITE
permissions to any non-superuser. When a non-superuser then attempts to
execute a COPY TO/FROM or any one of the generic file access functions, a
permission check is performed against the aliases for the user and target
directory. Superusers are allowed to bypass all of these checks. All
alias paths must be an absolute path in order to avoid potential risks.
However, in the generic file access functions superusers are still allowed
to execute the functions with a relative path where non-superusers are
required to provide an absolute path.

- Implementation Details -

System Catalog:
pg_diralias
- dirname - the name of the directory alias
- dirpath - the directory path - must be absolute
- diracl - the ACL for the directory

Syntax:
CREATE DIRALIAS <name> AS '<path>'
ALTER DIRALIAS <name> AS '<path>'
ALTER DIRALIAS <name> RENAME TO <new_name>
DROP DIRALIAS <name>

This is probably the area that I would really appreciate your thoughts and
recommendations. To GRANT permissions to a directory alias, I had to create
a special variant of GRANT since READ and WRITE are not reserved keywords
and causes grammar issues. Therefore, I chose to start with the following
syntax:

GRANT ON DIRALIAS <name> <permissions> TO <roles>

where <permissions> is either READ, WRITE or ALL.

Any comments, suggestions or feedback would be greatly appreciated.

Thanks,
Adam

--
Adam Brightwell - adam(dot)brightwell(at)crunchydatasolutions(dot)com
Database Engineer - www.crunchydatasolutions.com