[libvirt-users] [libvirt] Libvirtd running as root tries to access oneadmin (OpenNebula) NFS mount but throws: error: can’t canonicalize path
TomK
tk at mdevsys.com
Thu Apr 14 05:01:32 UTC 2016
On 4/13/2016 10:00 AM, John Ferlan wrote:
>
> On 04/13/2016 09:23 AM, TomK wrote:
>> On 4/13/2016 1:33 AM, Martin Kletzander wrote:
>>> On Tue, Apr 12, 2016 at 06:24:16PM -0400, TomK wrote:
>>>> On 4/12/2016 5:08 PM, John Ferlan wrote:
>>>>> 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...
>>>>>
>>>> Thanks John! Appreciated again.
>>>>
>>>> No worries, handle what's on the plate now and earmark this for checking
>>>> once you have some free cycles. I can temporarily hop on one leg by
>>>> using Martin Kletzander's workaround (It's a POC at the moment).
>>>>
>>>> I'll have a look at your instructions further but wanted to find out if
>>>> that config nfs.xml is a one time thing correct? I'm spinning these up
>>>> at will via the OpenNebula GUI and if I have update for each VM, that
>>>> breaks the Cloud provisioning. I'll go over your notes again. I'm
>>>> optimistic. :)
>>>>
>>> The more I'm thinking about it, the more I am convinced that the
>>> workaround is actually not a workaround. The only thing you need to do
>>> is having execute for others (precisely for 'nobody' on the nfs share)
>>> in the whole path on all directories. Without that even the pool won't
>>> be usable from libvirt. However it does not pose any security issue as
>>> it only allows others to check the path. When qemu is launched, it has
>>> the proper "label", meaning uid:gid to access the file so it will be
>>> able to read/write or whatever permissions you set there. It's just
>>> that libvirt does some checks that the path exists for example.
>>>
>>> Hope that's understandable and it will resolve your issue permanently.
>>>
>>> Have a nice day,
>>> Martin
>>>
>>>
>>> _______________________________________________
>>> libvirt-users mailing list
>>> libvirt-users at redhat.com
>>> https://www.redhat.com/mailman/listinfo/libvirt-users
>> The only reason I said that this might be a 'workaround' is due to John
>> Farlan commenting that he'll look at this later on. Ideally the
>> opennebula community keeps the other permissions to nill and presumably
>> they work on NFSv3 per the forum topic I included earlier from them.
>> But if setting the permissions on nobody to allow for the functionality,
>> I would be comfortable with that.
>>
> Martin and I were taking different paths... But yes, it certainly makes
> sense given your error message about canonical path and the need for
> eXecute permissions... I think I started wondering about that first, but
> then jumped into the NFS pool because that's what my reference point is
> for root-squash. Since root squash essentially sends root requests as
> "nfsnobody" (IOW: others not the user or group), then the "o+x" approach
> is the solution if you're going directly at the file.
>
> John
Yes, appears the o+x is the only way right now. It definitely tries to
access the share as root though, on CentOS 7 since I also tried to add
nfsnobody and nobody to the oneadmin group and that did not work
either. Seems OpenNebula doesn't have this issue with NFSv3 running on
Ubuntu:
[root at mdskvm-p01 ~]# rmdir /tmp/netfs-rootsquash-pool
[root at mdskvm-p01 ~]# cat nfs.xml
<pool type='netfs'>
<name>rootsquash</name>
<source>
<host name='opennebula01'/>
<dir path='/var/lib/one'/>
<format type='nfs'/>
</source>
<target>
<path>/tmp/netfs-rootsquash-pool</path>
<permissions>
<mode>0755</mode>
<owner>9869</owner>
<group>9869</group>
</permissions>
</target>
</pool>
[root at mdskvm-p01 ~]#
[root at mdskvm-p01 ~]#
[root at mdskvm-p01 ~]# virsh pool-define nfs.xml
Pool rootsquash defined from nfs.xml
[root at mdskvm-p01 ~]# virsh pool-build rootsquash
Pool rootsquash built
[root at mdskvm-p01 ~]# virsh pool-start rootsquash
error: Failed to start pool rootsquash
error: cannot open path '/tmp/netfs-rootsquash-pool': Permission denied
[root at mdskvm-p01 ~]# virsh vol-list rootsquash
error: Failed to list volumes
error: Requested operation is not valid: storage pool 'rootsquash' is
not active
[root at mdskvm-p01 ~]# ls -altri /tmp/netfs-rootsquash-pool
total 4
133 drwxrwxrwt. 14 root root 4096 Apr 14 00:05 ..
68785924 drwxr-xr-x 2 oneadmin oneadmin 6 Apr 14 00:05 .
[root at mdskvm-p01 ~]#
[root at mdskvm-p01 ~]# id oneadmin
uid=9869(oneadmin) gid=9869(oneadmin)
groups=9869(oneadmin),992(libvirt),36(kvm)
[root at mdskvm-p01 ~]# id nobody
uid=99(nobody) gid=99(nobody) groups=99(nobody),9869(oneadmin)
[root at mdskvm-p01 ~]# id nfsnobody
uid=65534(nfsnobody) gid=65534(nfsnobody)
groups=65534(nfsnobody),9869(oneadmin)
[root at mdskvm-p01 ~]# id root
uid=0(root) gid=0(root) groups=0(root)
[root at mdskvm-p01 ~]#
[root at mdskvm-p01 ~]# ps -ef|grep -i libvirtd
root 352 31058 0 00:31 pts/1 00:00:00 grep --color=auto -i
libvirtd
root 1459 1 0 Apr11 ? 00:07:40 /usr/sbin/libvirtd
--listen --config /etc/libvirt/libvirtd.conf
[root at mdskvm-p01 ~]#
[root at mdskvm-p01 ~]# umount /var/lib/one
[root at mdskvm-p01 ~]# mount --no-canonicalize /var/lib/one
[root at mdskvm-p01 ~]# umount /var/lib/one
[root at mdskvm-p01 ~]# mount /var/lib/one
[root at mdskvm-p01 ~]# mount|tail -n 1
192.168.0.70:/var/lib/one on /var/lib/one type nfs4
(rw,relatime,vers=4.0,rsize=8192,wsize=8192,namlen=255,soft,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.0.60,local_lock=none,addr=192.168.0.70)
[root at mdskvm-p01 ~]# umount /var/lib/one
[root at mdskvm-p01 ~]# mount --no-canonicalize /var/lib/one
[root at mdskvm-p01 ~]# mount|tail -n 1
192.168.0.70:/var/lib/one on /var/lib/one type nfs4
(rw,relatime,vers=4.0,rsize=8192,wsize=8192,namlen=255,soft,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=192.168.0.60,local_lock=none,addr=192.168.0.70)
[root at mdskvm-p01 ~]# su - oneadmin
Last login: Thu Apr 14 00:27:59 EDT 2016 on pts/0
[oneadmin at mdskvm-p01 ~]$ virsh -d 1 --connect qemu:///system create
/var/lib/one//datastores/0/47/deployment.0
create: file(optdata): /var/lib/one//datastores/0/47/deployment.0
error: Failed to create domain from
/var/lib/one//datastores/0/47/deployment.0
error: can't canonicalize path '/var/lib/one//datastores/0/47/disk.1':
Permission denied
[oneadmin at mdskvm-p01 ~]$
CONTROLLER ( NFS Server )
[oneadmin at opennebula01 one]$ ls -ld
/var{,/lib{,/one{,/datastores{,/0{,/47{,/disk.1}}}}}}
drwxr-xr-x. 19 root root 4096 Apr 4 21:26 /var
drwxr-xr-x. 28 root root 4096 Apr 13 03:30 /var/lib
drwxr-x---. 12 oneadmin oneadmin 4096 Apr 14 00:40 /var/lib/one
drwxrwxr-x 6 oneadmin oneadmin 46 Mar 31 02:44 /var/lib/one/datastores
drwxrwxr-x 8 oneadmin oneadmin 60 Apr 13 23:31
/var/lib/one/datastores/0
drwxrwxr-x 2 oneadmin oneadmin 68 Apr 13 23:32
/var/lib/one/datastores/0/47
-rw-r--r-- 1 oneadmin oneadmin 372736 Apr 13 23:32
/var/lib/one/datastores/0/47/disk.1
[oneadmin at opennebula01 one]$
NODE ( NFS Client )
[oneadmin at mdskvm-p01 ~]$ ls -ld
/var{,/lib{,/one{,/datastores{,/0{,/47{,/disk.1}}}}}}
drwxr-xr-x. 21 root root 4096 Apr 11 07:10 /var
drwxr-xr-x. 45 root root 4096 Apr 13 04:11 /var/lib
drwxr-x--- 12 oneadmin oneadmin 4096 Apr 14 00:39 /var/lib/one
drwxrwxr-x 6 oneadmin oneadmin 46 Mar 31 02:44 /var/lib/one/datastores
drwxrwxr-x 8 oneadmin oneadmin 60 Apr 13 23:31
/var/lib/one/datastores/0
drwxrwxr-x 2 oneadmin oneadmin 68 Apr 13 23:32
/var/lib/one/datastores/0/47
-rw-r--r-- 1 oneadmin oneadmin 372736 Apr 13 23:32
/var/lib/one/datastores/0/47/disk.1
[oneadmin at mdskvm-p01 ~]$
Cheers,
Tom K.
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