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Re: [libvirt-users] [libvirt] Libvirtd running as root tries to access oneadmin (OpenNebula) NFS mount but throws : error: can’t canonicalize path




On 04/12/2016 10:58 AM, TomK wrote:
> Hey Martin,
> 
> Thanks very much.  Appreciate you jumping in on this thread.

Can you provide some more details with respect to which libvirt version
you have installed. I know I've made changes in this space in more
recent versions (not the most recent). I'm no root_squash expert, but I
was the last to change things in the space so that makes me partially
fluent ;-) in NFS/root_squash speak.

Using root_squash is very "finicky" (to say the least)... It wasn't
really clear from what you posted how you are attempting to reference
things. Does the "/var/lib/one//datastores/0/38/deployment.0" XML file
use a direct path to the NFS volume or does it use a pool? If a pool,
then what type of pool? It is beneficial to provide as many details as
possible about the configuration because (so to speak) those that are
helping you won't know your environment (I've never used OpenNebula) nor
do I have a 'oneadmin' uid:gid.

What got my attention was the error message "initializing FS storage
file" with the "file:" prefix to the name and 9869:9869 as the uid:gid
trying to access the file (I assume that's oneadmin:oneadmin on your
system).

This says to me that you're trying to use a "file system" pool (e.g
<pool type="fs">) perhaps rather than the "NFS" pool (e.g. <pool
type="netfs">). Using an NFS pool certainly has the advantage of
"knowing how" to deal with the NFS environment. Since libvirt may
consider this to "just" be a FS file, then it won't necessarily know to
try to access the file properly (OK dependent upon libvirt version too
perhaps - the details have been paged out of my memory while I do other
work).

One other thing that popped out at me:

My /etc/exports has:

/home/bzs/rootsquash/nfs *(rw,sync,root_squash)

which only differs from yours by the 'no_subtree_check'

your environment though seems to have much more "depth" than mine. That
is you have "//datastores/0/38/disk.1" appended on as the (I assume)
disk to use. The question then becomes - does every directory in the
path to that file use "oneadmin:oneadmin" and of course does it have to
with[out] that extra flag.

Again, I'm no expert just trying to provide ideas and help...

John

> 
> You see, that's just it.  I've configured libvirt .conf files to run as
> oneadmin.oneadmin (non previlidged) for that NFS share and I can access
> all the files on that share as oneadmin without error, including the one
> you listed.  But libvirtd, by default, always starts as root.  So it's
> doing something as root, despite being configured to access the share as
> oneadmin.  As oneadmin I can access that file no problem.  Here's how I
> read the file off the node on which the NFS share is mounted on:
> 
> [oneadmin mdskvm-p01 ~]$ ls -altri /var/lib/one//datastores/0/38/disk.1
> 34642274 -rw-r--r-- 1 oneadmin oneadmin 372736 Apr 5 00:20
> /var/lib/one//datastores/0/38/disk.1
> [oneadmin mdskvm-p01 ~]$ file /var/lib/one//datastores/0/38/disk.1
> /var/lib/one//datastores/0/38/disk.1: # ISO 9660 CD-ROM filesystem data
> 'CONTEXT'
> [oneadmin mdskvm-p01 ~]$ strings /var/lib/one//datastores/0/38/disk.1|head
> CD001
> LINUX CONTEXT
> GENISOIMAGE ISO 9660/HFS FILESYSTEM CREATOR (C) 1993 E.YOUNGDALE (C)
> 1997-2006 J.PEARSON/J.SCHILLING (C) 2006-2007 CDRKIT TEAM 2016040500205600
> 2016040500205600
> 0000000000000000
> 2016040500205600
> 
> CD001
> 2016040500205600
> 2016040500205600
> [oneadmin mdskvm-p01 ~]$
> 
> My NFS mount looks as follows ( I have to use root_squash for security
> reasons.  I'm sure it will work using no_root_squash but that option is
> not an option here.):
> 
> [root mdskvm-p01 ~]# grep nfs /etc/fstab
> # 192.168.0.70:/var/lib/one/    /var/lib/one/  nfs  
> context=system_u:object_r:nfs_t:s0,soft,intr,rsize=8192,wsize=8192,noauto
> 192.168.0.70:/var/lib/one/      /var/lib/one/  nfs  
> soft,intr,rsize=8192,wsize=8192,noauto
> [root mdskvm-p01 ~]#
> 
> [root opennebula01 ~]# cat /etc/exports
> /var/lib/one/ *(rw,sync,no_subtree_check,root_squash)
> [root opennebula01 ~]#
> 
> 
> So I dug deeper and see that there is a possibility libvirtd is trying
> to access that NFS mount as root as some level because as root I also
> get a permission denied to the NFS share above.  Rightly so since I have
> root_squash that I need to keep.  But libvirtd should be able to access
> the file as oneadmin as I have above.  It's not and this is what I read
> on it:
> 
> https://www.redhat.com/archives/libvir-list/2014-May/msg00194.html
> 
> Comment is: "The current implementation works for local
> storage only and returns the canonical path of the volume."
> 
> But it seems the logic is applied to NFS mounts. Perhaps it shouldn't
> be?  Anyway to get around this problem?  This is CentOS 7 .
> 
> My post with OpenNebula is here from which this conversation originates:
> https://forum.opennebula.org/t/libvirtd-running-as-root-tries-to-access-oneadmin-nfs-mount-error-cant-canonicalize-path/2054/7
> 
> Cheers,
> Tom K.
> -------------------------------------------------------------------------------------
> 
> Living on earth is expensive, but it includes a free trip around the sun.
> 
> On 4/12/2016 10:03 AM, Martin Kletzander wrote:
>> On Mon, Apr 11, 2016 at 08:02:04PM -0400, TomK wrote:
>>> Hey All,
>>>
>>> Wondering if anyone had any suggestions on this topic?
>>>
>>
>> The only thing I can come up with is:
>> '/var/lib/one//datastores/0/38/disk.1': Permission denied
>>
>> ... that don't have access to that file.  Could you elaborate on that?
>>
>> I think it's either:
>>
>> a) you are running the domain as root or
>>
>> b) we don't use the domain's uid/gid to canonicalize the path.
>>
>> But if read access is enough for canonicalizing that path, I think the
>> problem is purely with permissions.
>>
>>> Cheers,
>>> Tom K.
>>> -------------------------------------------------------------------------------------
>>>
>>>
>>> Living on earth is expensive, but it includes a free trip around the
>>> sun.
>>>
>>> On 4/9/2016 11:08 AM, TomK wrote:
>>>> Adding in libvir-list.
>>>>
>>>> Cheers,
>>>> Tom K.
>>>> -------------------------------------------------------------------------------------
>>>>
>>>>
>>>> Living on earth is expensive, but it includes a free trip around the
>>>> sun.
>>>>
>>>> On 4/7/2016 7:32 PM, TomK wrote:
>>>>> Hey All,
>>>>>
>>>>> I've an issue where libvirtd tries to access an NFS mount but errors
>>>>> out with: can't canonicalize path '/var/lib/one//datastores/0 .  The
>>>>> unprevilidged user is able to read/write fine to the share.
>>>>> root_squash is used and for security reasons no_root_squash cannot be
>>>>> used.
>>>>>
>>>>> On the controller and node SELinux is disabled.
>>>>>
>>>>> [oneadmin mdskvm-p01 ~]$ virsh -d 1 --connect qemu:///system create
>>>>> /var/lib/one//datastores/0/38/deployment.0
>>>>> create: file(optdata): /var/lib/one//datastores/0/38/deployment.0
>>>>> error: Failed to create domain from
>>>>> /var/lib/one//datastores/0/38/deployment.0
>>>>> error: can't canonicalize path
>>>>> '/var/lib/one//datastores/0/38/disk.1': Permission denied
>>>>>
>>>>> I added some debug flags to get more info and added -x to the deploy
>>>>> script. Closest I get to more details is this:
>>>>>
>>>>> 2016-04-06 04:15:35.945+0000: 14072: debug :
>>>>> virStorageFileBackendFileInit:1441 : initializing FS storage file
>>>>> 0x7f6aa4009000 (file:/var/lib/one//datastores/0/38/disk.1)[9869:9869]
>>>>> 2016-04-06 04:15:35.954+0000: 14072: error :
>>>>> virStorageFileBackendFileGetUniqueIdentifier:1523 : can't
>>>>> canonicalize path '/var/lib/one//datastores/0/38/disk.1':
>>>>>
>>>>> https://www.redhat.com/archives/libvir-list/2014-May/msg00194.html
>>>>>
>>>>> Comment is: "The current implementation works for local
>>>>> storage only and returns the canonical path of the volume."
>>>>>
>>>>> But it seems the logic is applied to NFS mounts. Perhaps it shouldn't
>>>>> be?  Anyway to get around this problem?  This is CentOS 7 .
>>>>>
>>>>> Cheers,
>>>>> Tom K.
>>>>> -------------------------------------------------------------------------------------
>>>>>
>>>>>
>>>>> Living on earth is expensive, but it includes a free trip around the
>>>>> sun.
>>>>>
>>>>> _______________________________________________
>>>>> libvirt-users mailing list
>>>>> libvirt-users redhat com
>>>>> https://www.redhat.com/mailman/listinfo/libvirt-users
>>>>
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