Hi,
I'm starting working on an improvement for libvirt to be able to support
per-guest configurable user and group IDs for QEMU processes. Currently,
libvirt uses a configurable pair of user and group, which is defined in
qemu.conf, for all qemu processes when running in privileged mode.
This topic was already commented in qemu mailing list
(http://lists.nongnu.org/archive/html/qemu-devel/2011-10/msg00758.html)
but, as this requires changes in libvirt API, I'd like to discuss what
would be the best solution for it.
A solution (as proposed in the link above) would be to extend the
security driver model to allow multiple drivers. In this case, an
example of the XML definition would be:
...
<seclabel type='dynamic' model='selinux'>
<label>system_u:system_r:svirt_t:s0:c633,c712</label>
<imagelabel>system_u:object_r:svirt_image_t:s0:c633,c712</imagelabel>
</seclabel>
<seclabel type='dynamic' model='dac'>
<label>102:102</label>
<imagelabel>102:102</imagelabel>
</seclabel>
...
I don't know if this is a clean solution because the usual option would
be to enclose the block above in a "<seclabels>" tag. But as this would
break the actual API, it's not viable.
Another option is to expose the stack security driver that already
exists internally in libvirt (maybe extending it to support more than
two security drivers):
...
<seclabel type='stack'>
<seclabel type='dynamic' model='selinux'>
<label>system_u:system_r:svirt_t:s0:c633,c712</label>
<imagelabel>system_u:object_r:svirt_image_t:s0:c633,c712</imagelabel>
</seclabel>
<seclabel type='dynamic' model='dac'>
<label>102:102</label>
<imagelabel>102:102</imagelabel>
</seclabel>
</seclabel>
...
In that case, a nested seclabel only would be allowed when type='stack'.
Independently of how multiple security drivers can be expressed in the
XML, another problem would be how functions as virDomainGetSecurityLabel
should behave.
A third option is to just not support multiple security drivers and
include a new tag for DAC:
...
<seclabel type='dynamic' model='selinux'>
<label>system_u:system_r:svirt_t:s0:c633,c712</label>
<imagelabel>system_u:object_r:svirt_image_t:s0:c633,c712</imagelabel>
</seclabel>
<dac process='102:102' image='102:102'/>
...
Please let me know your opinions about this topic.
Regards,
Marcelo
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