Libguestfs - Nov 2014 - Re: libguestfs-tools with libvirt SASL authentication

Hello,

I'm running into an issue using the 'virt-df' command when SASL is
enabled in libvirt. I'm running version 1.26.5 of libguestfs on an Ubuntu
14.04 OS.

I'm running 'virt-df' for all guests at one time, not specifying a
domain or image to use. I was expecting a SASL authentication prompt but to no
avail. Below is a sample run:

root@all-in-one:~# virt-df -P 15
libvirt: XML-RPC error : authentication failed: Failed to start SASL
negotiation: -4 (SASL(-4): no mechanism available: No worthy mechs found)
virt-df: could not connect to libvirt (code 45, domain 7): authentication
failed: Failed to start SASL negotiation: -4 (SASL(-4): no mechanism available:
No worthy mechs found)

However, if I do specify a domain to run on, I am prompted for SASL
authentication:

root@all-in-one:~# virt-df -d instance-0000004d
libvirt needs authentication to connect to libvirt URI NULL
(see also: http://libvirt.org/auth.html http://libvirt.org/uri.html)
Please enter your authentication name: nova@all-in-one
Please enter your password:
Filesystem                           1K-blocks       Used  Available  Use%
instance-0000004d:/dev/sdb                 458        458          0  100%
instance-0000004d:/dev/sda1              22773      12223       9322   54%

Is there any way to successfully run 'virt-df' for all instances at once
while SASL is enabled in libvirt?


Thanks,
Dan Ryder

On Tue, Nov 04, 2014 at 06:47:04PM +0000, Dan Ryder (daryder)
wrote:
> Hello,
> 
> I'm running into an issue using the 'virt-df' command when SASL
is enabled in libvirt. I'm running version 1.26.5 of libguestfs on an Ubuntu
14.04 OS.
> 
> I'm running 'virt-df' for all guests at one time, not
specifying a domain or image to use. I was expecting a SASL authentication
prompt but to no avail. Below is a sample run:
> 
> root@all-in-one:~# virt-df -P 15
> libvirt: XML-RPC error : authentication failed: Failed to start SASL
negotiation: -4 (SASL(-4): no mechanism available: No worthy mechs found)
> virt-df: could not connect to libvirt (code 45, domain 7): authentication
failed: Failed to start SASL negotiation: -4 (SASL(-4): no mechanism available:
No worthy mechs found)
> 
> However, if I do specify a domain to run on, I am prompted for SASL
authentication:
> 
> root@all-in-one:~# virt-df -d instance-0000004d
> libvirt needs authentication to connect to libvirt URI NULL
> (see also: http://libvirt.org/auth.html http://libvirt.org/uri.html)
> Please enter your authentication name: nova@all-in-one
> Please enter your password:
> Filesystem                           1K-blocks       Used  Available  Use%
> instance-0000004d:/dev/sdb                 458        458          0  100%
> instance-0000004d:/dev/sda1              22773      12223       9322   54%
> 
> Is there any way to successfully run 'virt-df' for all instances at
once while SASL is enabled in libvirt?
I think this may be a bug.

virt-df has potentially 3(!) places where it can make a libvirt
connection, although only 2 of them are being used on Ubuntu.

(1) If you don't supply a list of domain names on the command line,
then virt-df will call libvirt to get them.  That happens in
df/domains.c:get_all_libvirt_domains:

  https://github.com/libguestfs/libguestfs/blob/master/df/domains.c#L72

If you supply a domain name, then this is not used.

(2) Secondly, virt-df calls into libguestfs (the C library) call
guestfs_add_domain() with a domain name parameter as a literal string,
either one fetched from (1) or one you passed on the command line.
Libguestfs then looks that up with libvirt to check it exists and to
get the list of disks.  That happens in
src/libvirt-auth.c:guestfs___open_libvirt_connection:

  https://github.com/libguestfs/libguestfs/blob/master/src/libvirt-auth.c#L192

(3) Finally if you are using the libvirt backend (which you are not on
Ubuntu) then there would be a third connection to run the appliance,
although it uses the same code as (2).

I believe the problem here is that (1) does not pass an auth handler.
ie. it calls virConnectOpenReadonly, not virConnectOpenAuth.  It's my
understanding that virConnectOpenReadonly bypasses the policy kit and
SASL stuff, but Dan Berrange (CC'd) will be able to tell me if I'm
correct about that.

If that was the case then you would see an error when virt-df tries to
get a list of domains.

Anyway, if it turns out to be a bug, please file it using the method
outlined on the front page of the website (or submit a patch!)

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top

Thanks for the info, Richard.


Hi Dan,

Any additional information on this?


Thanks,
Dan Ryder



-----Original Message-----
From: Richard W.M. Jones [mailto:rjones@redhat.com] 
Sent: Wednesday, November 05, 2014 8:46 AM
To: Dan Ryder (daryder); berrange@redhat.com
Cc: libguestfs@redhat.com
Subject: Re: [Libguestfs] libguestfs-tools with libvirt SASL authentication

On Tue, Nov 04, 2014 at 06:47:04PM +0000, Dan Ryder (daryder)
wrote:
> Hello,
> 
> I'm running into an issue using the 'virt-df' command when SASL
is enabled in libvirt. I'm running version 1.26.5 of libguestfs on an Ubuntu
14.04 OS.
> 
> I'm running 'virt-df' for all guests at one time, not
specifying a domain or image to use. I was expecting a SASL authentication
prompt but to no avail. Below is a sample run:
> 
> root@all-in-one:~# virt-df -P 15
> libvirt: XML-RPC error : authentication failed: Failed to start SASL 
> negotiation: -4 (SASL(-4): no mechanism available: No worthy mechs 
> found)
> virt-df: could not connect to libvirt (code 45, domain 7): 
> authentication failed: Failed to start SASL negotiation: -4 (SASL(-4): 
> no mechanism available: No worthy mechs found)
> 
> However, if I do specify a domain to run on, I am prompted for SASL
authentication:
> 
> root@all-in-one:~# virt-df -d instance-0000004d libvirt needs 
> authentication to connect to libvirt URI NULL (see also: 
> http://libvirt.org/auth.html http://libvirt.org/uri.html) Please enter 
> your authentication name: nova@all-in-one Please enter your password:
> Filesystem                           1K-blocks       Used  Available  Use%
> instance-0000004d:/dev/sdb                 458        458          0  100%
> instance-0000004d:/dev/sda1              22773      12223       9322   54%
> 
> Is there any way to successfully run 'virt-df' for all instances at
once while SASL is enabled in libvirt?
I think this may be a bug.

virt-df has potentially 3(!) places where it can make a libvirt connection,
although only 2 of them are being used on Ubuntu.

(1) If you don't supply a list of domain names on the command line, then
virt-df will call libvirt to get them.  That happens in
df/domains.c:get_all_libvirt_domains:

  https://github.com/libguestfs/libguestfs/blob/master/df/domains.c#L72

If you supply a domain name, then this is not used.

(2) Secondly, virt-df calls into libguestfs (the C library) call
guestfs_add_domain() with a domain name parameter as a literal string, either
one fetched from (1) or one you passed on the command line.
Libguestfs then looks that up with libvirt to check it exists and to get the
list of disks.  That happens in
src/libvirt-auth.c:guestfs___open_libvirt_connection:

  https://github.com/libguestfs/libguestfs/blob/master/src/libvirt-auth.c#L192

(3) Finally if you are using the libvirt backend (which you are not on
Ubuntu) then there would be a third connection to run the appliance, although it
uses the same code as (2).

I believe the problem here is that (1) does not pass an auth handler.
ie. it calls virConnectOpenReadonly, not virConnectOpenAuth.  It's my
understanding that virConnectOpenReadonly bypasses the policy kit and SASL
stuff, but Dan Berrange (CC'd) will be able to tell me if I'm correct
about that.

If that was the case then you would see an error when virt-df tries to get a
list of domains.

Anyway, if it turns out to be a bug, please file it using the method outlined on
the front page of the website (or submit a patch!)

Rich.

--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top
is 'top' for virtual machines.  Tiny program with many powerful
monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top