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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 03:55 PM, TomK wrote:
> 
> On 4/12/2016 3:40 PM, Martin Kletzander wrote:
>> [ I would be way easier to reply if you didn't top-post ]
>>
>> On Tue, Apr 12, 2016 at 12:07:50PM -0400, TomK wrote:
>>> Hey John,
>>>
>>> Hehe, I got the right guy then.  Very nice!  And very good ideas but I
>>> may need more time to reread and try them out later tonight. I'm fully
>>> in agreement about providing more details.  Can't be accurate in a
>>> diagnosis if there isn't much data to go on.  This pool option is new to
>>> me.  Please tell me more on it.  Can't find it in the file below but
>>> maybe it's elsewhere?
>>>
>>> ( <pool type="fs"> ) perhaps rather than the "NFS" pool ( e.g. <pool
>>> type="netfs"> )
>>>
>>>
>>> Allright, here's the details:
>>>
>>> [root mdskvm-p01 ~]# rpm -aq|grep -i libvir
>>> libvirt-daemon-driver-secret-1.2.17-13.el7_2.4.x86_64
>>> libvirt-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-driver-network-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-driver-lxc-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-driver-nwfilter-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-driver-interface-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-config-network-1.2.17-13.el7_2.4.x86_64
>>> libvirt-client-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-driver-qemu-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-driver-storage-1.2.17-13.el7_2.4.x86_64
>>> libvirt-python-1.2.17-2.el7.x86_64
>>> libvirt-glib-0.1.9-1.el7.x86_64
>>> libvirt-daemon-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-config-nwfilter-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-driver-nodedev-1.2.17-13.el7_2.4.x86_64
>>> libvirt-daemon-kvm-1.2.17-13.el7_2.4.x86_64
>>> [root mdskvm-p01 ~]# cat /etc/release
>>> cat: /etc/release: No such file or directory
>>> [root mdskvm-p01 ~]# cat /etc/*release*
>>> NAME="Scientific Linux"
>>> VERSION="7.2 (Nitrogen)"
>>> ID="rhel"
>>> ID_LIKE="fedora"
>>> VERSION_ID="7.2"
>>> PRETTY_NAME="Scientific Linux 7.2 (Nitrogen)"
>>> ANSI_COLOR="0;31"
>>> CPE_NAME="cpe:/o:scientificlinux:scientificlinux:7.2:GA"
>>> HOME_URL="http://www.scientificlinux.org//";
>>> BUG_REPORT_URL="mailto:scientific-linux-devel listserv fnal gov"
>>>
>>> REDHAT_BUGZILLA_PRODUCT="Scientific Linux 7"
>>> REDHAT_BUGZILLA_PRODUCT_VERSION=7.2
>>> REDHAT_SUPPORT_PRODUCT="Scientific Linux"
>>> REDHAT_SUPPORT_PRODUCT_VERSION="7.2"
>>> Scientific Linux release 7.2 (Nitrogen)
>>> Scientific Linux release 7.2 (Nitrogen)
>>> Scientific Linux release 7.2 (Nitrogen)
>>> cpe:/o:scientificlinux:scientificlinux:7.2:ga
>>> [root mdskvm-p01 ~]#
>>>
>>> [root mdskvm-p01 ~]# mount /var/lib/one
>>> [root mdskvm-p01 ~]# su - oneadmin
>>> Last login: Sat Apr  9 10:39:25 EDT 2016 on pts/0
>>> Last failed login: Tue Apr 12 12:00:57 EDT 2016 from opennebula01 on
>>> ssh:notty
>>> There were 9584 failed login attempts since the last successful login.
>>> i[oneadmin mdskvm-p01 ~]$ id oneadmin
>>> uid=9869(oneadmin) gid=9869(oneadmin)
>>> groups=9869(oneadmin),992(libvirt),36(kvm)
>>> [oneadmin mdskvm-p01 ~]$ pwd
>>> /var/lib/one
>>> [oneadmin mdskvm-p01 ~]$ ls -altriR|grep -i root
>>> 134320262 drwxr-xr-x. 45 root     root        4096 Apr 12 07:58 ..
>>> [oneadmin mdskvm-p01 ~]$
>>>
>>>

It'd take more time than I have at the present moment to root out what
changed when for NFS root-squash, but suffice to say there were some
corner cases.  Some involving how qemu-img files are generated - I don't
have the details present in my short term memory.

>>>
>>> [oneadmin mdskvm-p01 ~]$ cat /var/lib/one//datastores/0/38/deployment.0
>>> <domain type='kvm'
>>> xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
>>>         <name>one-38</name>
>>>         <vcpu>1</vcpu>
>>>         <cputune>
>>>                 <shares>1024</shares>
>>>         </cputune>
>>>         <memory>524288</memory>
>>>         <os>
>>>                 <type arch='x86_64'>hvm</type>
>>>                 <boot dev='hd'/>
>>>         </os>
>>>         <devices>
>>> <emulator>/usr/libexec/qemu-kvm</emulator>
>>>                 <disk type='file' device='disk'>
>>>                         <source
>>> file='/var/lib/one//datastores/0/38/disk.0'/>
>>>                         <target dev='hda'/>
>>>                         <driver name='qemu' type='qcow2' cache='none'/>
>>>                 </disk>
>>>                 <disk type='file' device='cdrom'>
>>>                         <source
>>> file='/var/lib/one//datastores/0/38/disk.1'/>
>>>                         <target dev='hdb'/>
>>>                         <readonly/>
>>>                         <driver name='qemu' type='raw'/>
>>>                 </disk>
>>>                 <interface type='bridge'>
>>>                         <source bridge='br0'/>
>>>                         <mac address='02:00:c0:a8:00:64'/>
>>>                 </interface>
>>>                 <graphics type='vnc' listen='0.0.0.0' port='5938'/>
>>>         </devices>
>>>         <features>
>>>                 <acpi/>
>>>         </features>
>>> </domain>
>>>
>>> [oneadmin mdskvm-p01 ~]$ cat
>>> /var/lib/one//datastores/0/38/deployment.0|grep -i nfs
>>> [oneadmin mdskvm-p01 ~]$
>>>

Having/using a root squash via an NFS pool is "easy" (famous last words)

Create some pool XML (taking the example I have)

% cat nfs.xml
<pool type='netfs'>
    <name>rootsquash</name>
    <source>
        <host name='localhost'/>
        <dir path='/home/bzs/rootsquash/nfs'/>
        <format type='nfs'/>
    </source>
    <target>
        <path>/tmp/netfs-rootsquash-pool</path>
        <permissions>
            <mode>0755</mode>
            <owner>107</owner>
            <group>107</group>
        </permissions>
    </target>
</pool>

In this case 107:107 is qemu:qemu and I used 'localhost' as the
hostname, but that can be a fqdn or ip-addr to the NFS server.

You've already seen my /etc/exports

virsh pool-define nfs.xml
virsh pool-build rootsquash
virsh pool-start rootsquash
virsh vol-list rootsquash

Now instead of

   <disk type='file' device='disk'>
     <source file='/var/lib/one//datastores/0/38/disk.0'/>
     <target dev='hda'/>
     <driver name='qemu' type='qcow2' cache='none'/>
   </disk>

Something like:

  <disk type='volume' device='disk'>
    <driver name='qemu' type='qemu' cache='none'/>
    <source pool='rootsquash' volume='disk.0'/>
    <target dev='hda'/>
  </disk>

The volume name may be off, but it's perhaps close.  I forget how to do
the readonly bit for a pool (again, my focus is elsewhere).

Of course you'd have to adjust the nfs.xml above to suit your
environment and see what you see/get.  The privileges for the pool and
volumes in the pool become the key to how libvirt decides to "request
access" to the volume.  "disk.1" having read access is probably not an
issue since you seem to be using it as a CDROM; however, "disk.0" is
going to be used for read/write - thus would have to be appropriately
configured...

>>>
>>>
>>> Cheers,
>>> Tom K.
>>> -------------------------------------------------------------------------------------
>>>
>>>
>>> Living on earth is expensive, but it includes a free trip around the
>>> sun.
>>>
>>> On 4/12/2016 11:45 AM, John Ferlan wrote:
>>>>
>>>> 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.
>>>>
>>
>> I'm always lost in how do we handle *all* the corner cases that are not
>> even used anywhere at all, but care about the conditions we have in the
>> code.  Especially when it's constantly changing.  So thanks for jumping
>> in.  I only replied because nobody else did and I had only the tiniest
>> clue as to what could happen.
>>

I saw the post, but was heads down somewhere else. Suffice to say trying
to swap in root_squash is a painful exercise...


John

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