Access control for CASTOR storage elements

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This page is part of an investigation on How to control access rights for LFC/SRM files .

Note: CASTOR is currently not being used in the Netherlands. It is included in this investigation for the sake of completeness. Also, as there are no Dutch CASTOR systems we cannot use proxies for the Dutch VOs that were used for the other storage elements. For CASTOR we will use a dteam proxy.

Finding out which storage systems are available

There are only a few CASTOR storage systems in use within EGEE. A Google search came up with one that is accessible for the dteam VO: 

12983000000     1003000000      n.a     srm-dteam.gridpp.rl.ac.uk

Note #1 before using the srm* commands make sure that the SRM client is at least 2.1.0 as otherwise most, if not all, srm* commands will fail: 

$ srmping -version
Storage Resource Manager (SRM) Client version 2.1.0
Copyright (c) 2002-2008 Fermi National Accelerator Laborator

Note #2 The glite 3.2 UI up to version 3.2.4 contains an older (actually, too old !) version of the srm-client than the glite 3.1 UI !

You can use the srmping command to get some basic information about a storage system 

$ srmping -2  srm://srm-dteam.gridpp.rl.ac.uk/
VersionInfo : v2.2
SRM version:v2_7_15
backend_type:CASTOR
backend_version:2.1.7
Nb of active CASTOR threads:0

So host srm-dteam.gridpp.rl.ac.uk is a SRMv2.2 compliant storage system based on CASTOR.

Finding out how storage is organized

You can use the srmls command to figure out how the storage is organized: 

$ srmls -l srm://srm-dteam.gridpp.rl.ac.uk/
srm client error:
java.lang.Exception: Return status:
 - Status code:  SRM_FAILURE
 - Explanation:  Failed for all paths

It seems that CASTOR does not allow the listing of arbitary remote directories. By looking at a file that was previously stored on this host (using lcg-lr) we guess that the directory structure starts with the prefix: 

/castor/ads.rl.ac.uk/test/dteam/disk0tape0

However, an srmls on this directory returns: 

srm client error:
java.lang.Exception: Return status:
 - Status code:  SRM_TOO_MANY_RESULTS
 - Explanation:

but we can list the generated directory: 

$ srmls srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated
 /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-01-23/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-01-26/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-03-06/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-03-16/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-03-18/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-04-30/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-05-01/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-05-07/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-05-14/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-05-29/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-06-11/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-06-12/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-06-19/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-06-23/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-06-24/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-13/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-15/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-16/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-20/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-21/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-22/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-23/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-24/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-25/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-26/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-27/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-28/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-29/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-07-31/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-08-04/
     /castor/ads.rl.ac.uk/test/dteam/disk0tape0/generated/2009-08-20/

Creating your own directory in SRM-space

Before we copy a file to the CASTOR SRM we first create our own directory. If we do not do this then SRM will store the files in generated directories, over which we have little or no control. 

 srmmkdir srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/dteam/disk0tape0/janjust

The URL for this directory will be used throughout the rest of this page, hence we abbreviate it to 

SRM=srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/dteam/disk0tape0/janjust

Copying and registering your file

Next we will copy a file to our SRM directory and register it in the LFC in one go: 

$ lcg-cr -d $SRM/myfile -l lfn:/grid/pvier/janjust/my-castor-file file://$PWD/myfile
 guid:0e56765a-5e1c-495e-a997-4495a4f06f18

which returns the LFC GUID for the file upon success.

Note: the LFC location is /grid/pvier/janjust which was actually a mistake. However, the LFC allows me to write to this directory even though I used a dteam proxy !!

(For details on how to find out how the LFC directory space is organized see Access control for the LFC)

We could also have copied the file to the SRM only, bypassing the LFC registration, using the command 

lcg-cp file://$PWD/myfile $SRM/myfile

or even 

srmcp -globus_tcp_port_range=20000,25000 file://$PWD/myfile $SRM/myfile

but as we needed the LFC entry as well we used the (preferred) lcg-cr command. Please also note that the srmcp command is not very well supported.

Looking at the permissions

For a file that is copied to SRM and that is registered in the LFC there are 2 sets of permissions:

  1. SRM-level
  2. LFC-level

These permissions are not directly related to each other and need to be modified separately. In this section we explain how to modify the SRM-level permissions. The LFC-level permissions are explained in Access control for the LFC. 

$ srm-get-permissions $SRM/myfile
# file  : srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/dteam/disk0tape0/janjust/myfile
# owner : dteam001
owner:dteam001:RWX
user:dteam001:RWX
group:dteam:RWX
other:RW

Just for the fun of it, let's list a file which we did not create ourselves: 

$ srm-get-permissions srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/atlas/atlasTest/nopolicy2
# file  : srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/atlas/atlasTest/nopolicy2
# owner : gtf
owner:gtf:RW
user:gtf:RW
group:sysgroup:R
other:R

When you compare it to dCache (see Access control for dCache storage elements) this looks more like "regular" UNIX permissions:

  • the file is owned by a single user
  • there are 'group' and 'other' permissions

but there are subtle differences!

We will have to keep this in mind when we want to limit access to our files.

Modifying the permissions

Use 

srm-set-permissions -h

to get a list of options for this command. 

$ srm-set-permissions -type=CHANGE -group=NONE -other=NONE $SRM/myfile
Return code: SRM_INVALID_REQUEST
Explanation: Group 500 does not exist

Don't you just love these kind of error messages? Some experimentation shows that the -group=NONE part is wreaking havoc: 

$ srm-set-permissions -type=CHANGE -other=NONE  $SRM/myfile

returns no errors, but ... 

$ srm-get-permissions $SRM/myfile
# file  : srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/dteam/disk0tape0/janjust/myfile
# owner : dteam001
owner:dteam001:RWX
user:dteam001:RWX
group:dteam:RW
other:R             # <------------- !!!!!

it also did not do what we expected: the other permissions are still R but we requested 'NONE'.

There are other ways of using srm-set-permissions. Let's see what that gives: 

$ srm-set-permissions -type=REMOVE -group=RWX  $SRM/myfile
Return code: SRM_INVALID_REQUEST
Explanation: Group 500 does not exist

No change. Next: 

$ srm-set-permissions -type=REMOVE -other=RWX  $SRM/myfile

Ah, that command did work: the intention of this command was to remove the permissions RWX for the other group. Let's see what the permissions are now: 

$ srm-get-permissions $SRM/myfile
# file  : srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/dteam/disk0tape0/janjust/myfile
# owner : dteam001
owner:dteam001:NONE
user:dteam001:NONE
group:dteam:NONE
other:NONE

Now ALL permissions are gone ?!?!?!? This just keeps getting better and better, doesn't it ;-) ?

Verifying access control

As the original user: 

$ srm-get-permissions $SRM/myfile
# file  : srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/dteam/disk0tape0/janjust/myfile
# owner : dteam001
owner:dteam001:NONE
user:dteam001:NONE
group:dteam:NONE
other:NONE

Let's try to read it: 

$ lcg-cp $SRM/myfile file://$PWD/blah
globus_ftp_client: the server responded with an error
500 Command failed. : open error: Permission denied

lcg_cp: Permission denied

Well, at least the permissions are consistent with the lcg-cp command.

Let's give access back to the owner: 

$ srm-set-permissions -type=ADD -owner=RWX  $SRM/myfile

And try again: 

$ srm-get-permissions $SRM/myfile
# file  : srm://srm-dteam.gridpp.rl.ac.uk/castor/ads.rl.ac.uk/test/dteam/disk0tape0/janjust/myfile
# owner : dteam001
owner:dteam001:RWX
user:dteam001:RWX
group:dteam:NONE
other:NONE

$ lcg-cp $SRM/myfile file://$PWD/blah 
$ ls -al blah
-rw-r--r--  1 janjust datagrid 8508 Aug 20 16:49 blah

so at least we can copy the file again.

Now if we switch to another VO: 

$  voms-proxy-init --voms pvier
Enter GRID pass phrase:
Your identity: /O=dutchgrid/O=users/O=nikhef/CN=Jan Just Keijser
Creating temporary proxy ........................................................ Done
Contacting  voms.grid.sara.nl:30000 [/O=dutchgrid/O=hosts/OU=sara.nl/CN=voms.grid.sara.nl] "pvier" Done
Creating proxy ........................................................... Done
Your proxy is valid until Fri Aug 21 05:18:15 2009

and then try to copy the file 

$ lcg-cp $SRM/myfile file://$PWD/blah

we get NO error message.

Let's create a VO-less proxy and try again: 

$ grid-proxy-init -old
Your identity: /O=dutchgrid/O=users/O=nikhef/CN=Jan Just Keijser
Enter GRID pass phrase for this identity:
Creating proxy ....................................................... Done
Your proxy is valid until: Fri Aug 21 05:22:13 2009

$ voms-proxy-info -all
WARNING: Unable to verify signature! Server certificate possibly not installed.
Error: VOMS extension not found!
subject   : /O=dutchgrid/O=users/O=nikhef/CN=Jan Just Keijser/CN=proxy
issuer    : /O=dutchgrid/O=users/O=nikhef/CN=Jan Just Keijser
identity  : /O=dutchgrid/O=users/O=nikhef/CN=Jan Just Keijser
type      : proxy
strength  : 512 bits
path      : /tmp/x509up_u7651
timeleft  : 11:59:59

$ lcg-cp $SRM/myfile file://$PWD/blah

And again, we get NO error message.

Next we ask a colleague to try it as well and he also gets NO error message !!

Some investigation shows that the gridmap-file on the CASTOR nodes maps all users for a particular VO to a single userid dteam001. So even though the group permissions are now gone anybody who is mapped to this userid can read/write/delete my files.

Conclusion

Access control in CASTOR is not very well implemented:

  • The srm-{get,set}-permissions commands do work but not in a comprehensible manner.
  • The fact that multiple users, regardless of the VOMS-extensions in their proxies, are mapped to a single userid makes access control useless.
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