[libvirt] [PATCH 3/3] security_dac: Favour ACLs over chown()

[Daniel P. Berrange]

On Wed, Aug 28, 2013 at 12:27:40PM +0200, Michal Privoznik wrote:
> On filesystems supporting ACLs we don't need to do a chown but we
> can just set ACLs to gain access for qemu. However, since we are
> setting these on too low level, where we don't know if disk is
> just a read only or read write, we set read write access
> unconditionally.
> 
> >From implementation POV, a reference counter is introduced, so ACL is
> restored only on the last restore attempt in order to not cut off other
> domains. And since a file may had an ACL for a user already set, we need
> to keep this as well. Both these, the reference counter and original ACL
> are stored as extended attributes named trusted.libvirt.dac.refCount and
> trusted.libvirt.dac.oldACL respectively.
> 
> However, some filesystems doesn't support ACLs, XATTRs, or both. So the
> code is made to favour ACLs among with tracking the reference count. If
> this fails, we fall back to chown()  with best effort to remember the
> original owner of file.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/security/security_dac.c | 297 +++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 268 insertions(+), 29 deletions(-)
> 
> diff --git a/src/security/security_dac.c b/src/security/security_dac.c
> index 8cbb083..913b68e 100644
> --- a/src/security/security_dac.c
> +++ b/src/security/security_dac.c
> @@ -37,6 +37,9 @@
>  
>  #define VIR_FROM_THIS VIR_FROM_SECURITY
>  #define SECURITY_DAC_NAME "dac"
> +#define SECURITY_DAC_XATTR_OLD_ACL "trusted.libvirt.dac.oldACL"
> +#define SECURITY_DAC_XATTR_OLD_OWNER "trusted.libvirt.dac.oldOwner"
> +#define SECURITY_DAC_XATTR_REFCOUNT "trusted.libvirt.dac.refCount"

Use of "trusted." is non-portable, per the long mail thread last
time this was posted[1]. The discussion there was never resolved in
any way, so NACK to this patch as is.

Daniel

[1] https://www.redhat.com/archives/libvir-list/2013-March/msg01610.html
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