Difference between revisions of "Access control for dCache storage elements"
| Line 105: | Line 105: | ||
We will have to keep this in mind when we want to limit access to our files. | We will have to keep this in mind when we want to limit access to our files. | ||
| − | '''Note''': this limitation is due to the setup of dCache , where <tt>pnfs</tt> is used as the underlying file system. | + | '''Note''': this limitation is due to the setup of the dCache storage system at SARA, where <tt>pnfs</tt> is used as |
| + | the underlying file system. | ||
<tt>pnfs</tt> does not support user-level access control. An alternative is to use <tt>chimera</tt> as the underlying | <tt>pnfs</tt> does not support user-level access control. An alternative is to use <tt>chimera</tt> as the underlying | ||
file system, which does support user-level ACLs, but this would require a migration of '''all''' data currently in | file system, which does support user-level ACLs, but this would require a migration of '''all''' data currently in | ||
| Line 112: | Line 113: | ||
= Modifying the permissions = | = 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 | ||
| + | (this command does not return any output on success) | ||
| + | |||
| + | '''Note''' that we have set the group permissions to <NONE> . If we do not do this then users from other VOs can still read the file. | ||
= Verifying access control = | = 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! | ||
| + | |||
| + | '''Note''' that the dCache server has mapped the voms proxy to a different user (18002), which causes the | ||
| + | <tt>srmcp</tt> request to fail. Thus dCache user+group mappings are slightly different from UNIX user+group | ||
| + | mappings: in dCache: | ||
| + | * 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. | ||
Revision as of 11:55, 6 August 2009
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://srm.grid.sara.nl
512 //
[SNIP]
4096 //pnfs/
[SNIP]
This listing tells us that this storage system uses a PNFS file system, which means that we're talking to a dCache SRM. Subsequent srmls commands then give us:
$ srmls srm://srm.grid.sara.nl/pnfs/
512 /pnfs//
512 /pnfs//grid.sara.nl/
[SNIP]
$ srmls srm://srm.grid.sara.nl/pnfs/grid.sara.nl
512 /pnfs/grid.sara.nl/
512 /pnfs/grid.sara.nl/disk/
512 /pnfs/grid.sara.nl/tapetests/
512 /pnfs/grid.sara.nl/data/
512 /pnfs/grid.sara.nl/disktests/
$ srmls srm://srm.grid.sara.nl/pnfs/grid.sara.nl/data
0 /pnfs/grid.sara.nl/data/
[SNIP}
512 /pnfs/grid.sara.nl/data/pvier/
512 /pnfs/grid.sara.nl/data/vlemed/
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 dCache 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.grid.sara.nl/pnfs/grid.sara.nl/data/pvier/janjust/
The URL for this directory will be used throughout the rest of this page, hence we abbreviate it to
SRM=srm://srm.grid.sara.nl/pnfs/grid.sara.nl/data/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 $SRM/myfile -l lfn:/grid/pvier/janjust/myfile file://$PWD/myfile
which, if successful, returns the LFC GUID for the file
guid:6b4c060f-cd95-4360-9e1b-a29d023d49b8
(For details on how to find out how the LFC directory space is organized see below)
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.
$ 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:R other:R
Just for the fun of it, let's list a file which we did not create ourselves:
$ srm-get-permissions srm://srm.grid.sara.nl/pnfs/grid.sara.nl/data/pvier/ronstestdir3 # file : srm://srm.grid.sara.nl/pnfs/grid.sara.nl/data/pvier/ronstestdir3 # owner : 18010 owner:18010:RWX user:18010:RWX group:1276:NONE other:NONE
Wait a second... that file has exactly the same user (18010) and group (1276) !
Now let's check a directory that was created using a different VOMS proxy, this time one for VO vlemed:
$ srm-get-permissions srm://srm.grid.sara.nl/pnfs/grid.sara.nl/data/vlemed/generated/2007-11-07 # file : srm://srm.grid.sara.nl/pnfs/grid.sara.nl/data/vlemed/generated/2007-11-07 # owner : 18002 owner:18002:RWX user:18002:RWX group:1276:RX other:RX
This time the user is different (18002) but the group is still 1276 ! We will have to keep this in mind when we want to limit access to our files.
Note: this limitation is due to the setup of the dCache storage system at SARA, where pnfs is used as the underlying file system. pnfs does not support user-level access control. An alternative is to use chimera as the underlying file system, which does support user-level ACLs, but this would require a migration of all data currently in dCache, as well as a (manual) re-synchronization between dCache and all LFCs that have entries pointing to dCache.
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
(this command does not return any output on success)
Note that we have set the group permissions to <NONE> . If we do not do this then users from other VOs can still read the file.
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!
Note that 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: in dCache:
- 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.
