Access control for DPM storage elements
This page is part of an investigation on How to control access rights for LFC/SRM files .
Finding out how storage is organized
To list the storage systems to which you have access use
lcg-infosites --vo <YOUR-VO> se
which results in
Avail Space(Kb) Used Space(Kb) Type SEs ---------------------------------------------------------- 12078 108 n.a srm.grid.rug.nl 12078 108 n.a srm.grid.rug.nl 730582644 681194097 n.a gb-se-amc.amc.nl 8226695519985 23304480014 n.a srm.grid.sara.nl 605355546 806421195 n.a gb-se-nki.els.sara.nl 6575746866 20920246 n.a carme.htc.biggrid.nl 152913518 115521938 n.a se.grid.rug.nl 248345185 1166074827 n.a gb-se-ams.els.sara.nl 355230761 1056545980 n.a gb-se-uu.science.uu.nl 1266740857 145035883 n.a gb-se-wur.els.sara.nl 337812899 1076607113 n.a gb-se-kun.els.sara.nl 2195706454 3048365 n.a tbn18.nikhef.nl 771834491 620488567 n.a gb-se-lumc.lumc.nl
Note the current version of the lcg-infosites command does not use your grid proxy at all !
You can then use the srmls command to figure out how the storage is organized:
$ srmls srm://tbn18.nikhef.nl SRMClientV2 : srmLs: try # 0 failed with error SRMClientV2 : Method 'ns1:srmLs' not implemented: method name or namespace not recognized SRMClientV2 : srmLs: try again
Ah... this is a SRMv1 interface, which does not support the srmLs command. The SRMv2 interface for DPM installations is on port 8446 by default.
$ srmls srm://tbn18.nikhef.nl:8446/
0 //
0 //dpm/
Note the extra slash ('/') at the end of the command!
So yes, we are talking to a DPM server. Subsequent srmls commands then give us:
$ srmls srm://tbn18.nikhef.nl:8446/dpm
0 /dpm/
0 /dpm/nikhef.nl/
$ srmls srm://tbn18.nikhef.nl:8446/dpm/nikhef.nl
0 /dpm/nikhef.nl/
0 /dpm/nikhef.nl/home/
$ srmls srm://tbn18.nikhef.nl:8446/dpm/nikhef.nl/home
0 /dpm/nikhef.nl/home/
[SNIP]
0 /dpm/nikhef.nl/home/pvier/
0 /dpm/nikhef.nl/home/vlemed/
[SNIP]
Hey, we are at the VO level now. Here I've listed the two VOs which will be used throughout this page.
Creating your own directory in SRM-space
Before we copy a file to the DPM 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://tbn18.nikhef.nl:8446/dpm/nikhef.nl/home/pvier/janjust
The URL for this directory will be used throughout the rest of this page, hence we abbreviate it to
SRM=srm://tbn18.nikhef.nl:8446/dpm/nikhef.nl/home/pvier/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 $SRM/myfile -l lfn:/grid/pvier/janjust/my-dpm-file file://$PWD/myfile guid:bbdad839-b2d1-46f6-95ab-5b6561f7e72f
which returns the LFC GUID for the file upon success.
(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
srmcp file://$PWD/myfile $SRM/myfile
but as we needed the LFC entry as well we used the (preferred) lcg-cr command.
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:
- SRM-level
- 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.
First we try the "standard" srm-get-permissions command:
$ srm-get-permissions $SRM/myfile srm client error: java.lang.NullPointerException
Eh? It turns out that this is a bug: https://gus.fzk.de/ws/ticket_info.php?ticket=50779
Luckily there is another way of looking at DPM permissions:
$ export DPNS_HOST=tbn18.nikhef.nl $ dpns-getacl /dpm/nikhef.nl/home/pvier/janjust/myfile # file: /dpm/nikhef.nl/home/pvier/janjust/myfile # owner: /O=dutchgrid/O=users/O=nikhef/CN=Jan Just Keijser # group: pvier user::rw- group::rw- #effective:rw- group:pvier/Role=production:rwx #effective:rw- group:pvier/Role=lcgadmin:rwx #effective:rw- mask::rw- other::r--
Notes
- the dpns-* commands look at the DPNS_HOST environment variable to determine which server to talk to
- the dpns-* commands do not use srm:// URLs so we need to strip off the srm://tbn18.nikhef.nl part
Just for the fun of it, let's list a file which we did not create ourselves:
$ dpns-getacl /dpm/nikhef.nl/home/vlemed/foo.txt # file: /dpm/nikhef.nl/home/vlemed/foo.txt # owner: /O=dutchgrid/O=users/O=uva/OU=wins/CN=Tristan Glatard # group: vlemed user::rw- group::rw- #effective:rw- group:vlemed/Role=production:rwx #effective:rw- group:vlemed/Role=lcgadmin:rwx #effective:rw- mask::rw- 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 is a difference
- there are multiple group permissions
We will have to keep this in mind when we want to limit access to our files.
Modifying the permissions
We would want to use the srm-set-permissions command to modify the permissions, but similar to srm-get-permissions this command does not work on DPM servers.
Instead we use dpns-setacl. Use
$ man dpns-setacl
for a full manual page, as there are many options for this command.
For our example we wish to
- remove the default group bits
- remove the mask (to make sure other groups do not inherit permissions)
- remove the otherbits
dpns-setacl -m g::0,m:0,o::0 /dpm/nikhef.nl/home/pvier/janjust/myfile
DPM and the dpns-setacl command can do very fine-grained access control on files and directories, yet that falls outside the scope of this investigation.
Verifying access control
As the original user:
$ srm-get-permissions $SRM/myfile # file : srm://srm.grid.sara.nl/pnfs/grid.sara.nl/data/pvier/janjust/myfile # owner : 18010 owner:18010:RW user:18010:RW group:1276:NONE other:NONE
Now if we switch to another VO:
$ voms-proxy-init --voms vlemed 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:30003 [/O=dutchgrid/O=hosts/OU=sara.nl/CN=voms.grid.sara.nl] "vlemed" Done Creating proxy ............................. Done Your proxy is valid until Thu Aug 6 23:45:56 2009
and then try to copy the file
$ srmcp $SRM/myfile file://$PWD/blah Thu Aug 06 11:46:41 CEST 2009: rs.state = Failed rs.error = at Thu Aug 06 11:46:36 CEST 2009 state Pending : created RequestFileStatus#-2083337326 failed with error:[ at Thu Aug 06 11:46:36 CEST 2009 state Failed : user AR:3209444168817257963 vlemed /O=dutchgrid/O=users/O=nikhef/CN=Jan Just Keijser 18002 read-write 0 / / < 1 groupLists : GL:/vlemed 1 groups : [1276,]; >cannot read 00190000000000000018C718] Thu Aug 06 11:46:41 CEST 2009: java.io.IOException: rs.state = Failed rs.error = at Thu Aug 06 11:46:36 CEST 2009 state Pending : created RequestFileStatus#-2083337326 failed with error:[ at Thu Aug 06 11:46:36 CEST 2009 state Failed : user AR:3209444168817257963 vlemed /O=dutchgrid/O=users/O=nikhef/CN=Jan Just Keijser 18002 read-write 0 / / < 1 groupLists : GL:/vlemed 1 groups : [1276,]; >cannot read 00190000000000000018C718] srm copy of at least one file failed or not completed
We can no longer access the file: success!
Notes
- it currently is not possible with dCache PNFS to restrict access to a file for your fellow VO-members.
- the dCache server has mapped the voms proxy to a different user (18002), which causes the srmcp request to fail. Thus dCache user+group mappings are slightly different from UNIX user+group mappings:
- user+group1 = dcache_user1
- user+group2 = dcache_user2
whereas on a regular UNIX filesystem you can always access a file that is owned by you, regardless of the groupid of the file.
